Project: Firecracker (Runtime / Container Runtime)
File: CHANGELOG.md

All notable changes to this project will be documented in this file. The format is based on , and this project adheres to . : Added ACPI support to Firecracker for x86_64 microVMs. Currently, we pass ACPI tables with information about the available vCPUs, interrupt controllers, VirtIO and legacy x86 devices to the guest. This allows booting kernels without MPTable support. Please see our for more information regarding relevant kernel configurations. : Added support for the Virtual Machine Generation Identifier (VMGenID) device on x86_64 platforms. VMGenID is a virtual device that allows VMMs to notify guests when they are resumed from a snapshot. Linux includes VMGenID support since version 5.18. It uses notifications from the device to reseed its internal CSPRNG. Please refer to and documention for more info on VMGenID. VMGenID state is part of the snapshot format of Firecracker. As a result, Firecracker snapshot version is now 2.0.0. : Changed `--config` parameter of `cpu-template-helper` optional. Users no longer need to prepare kernel, rootfs and Firecracker configuration files to use `cpu-template-helper`. Changed T2CL template to pass through bit 27 and 28 of `MSRIA32ARCH_CAPABILITIES` (`RFDSNO` and `RFDSCLEAR`) since KVM consider they are able to be passed through and T2CL isn't designed for secure snapshot migration between different processors. Changed T2S template to set bit 27 of `MSRIA32ARCHCAPABILITIES` (`RFDSNO`) to 1 since it assumes that the fleet only consists of processors that are not affected by RFDS. : Avoid setting `kvmimmediateexit` to 1 if are already handling an exit, or if the vCPU is stopped. This avoids a spurious KVM exit upon restoring snapshots. : Do not initialize vCPUs in powered-off state upon snapshot restore. No functional change, as vCPU initialization is only relevant for the booted case (where the guest expects CPUs to be powered off). Firecracker's `--start-time-cpu-us` and `--start-time-us` parameters are deprecated and will be removed in v2.0 or later. They are used by the jailer to pass the value that should be subtracted from the (CPU) time, when emitting the `starttimeus` and `starttimecpu_us` metrics. These parameters were never meant to be used by end customers, and we recommend doing any such time adjustments outside Firecracker. Booting with microVM kernels that rely on MPTable on x86_64 is deprecated and support will be removed in v2.0 or later. We suggest to users of Firecracker to use guest kernels with ACPI support. For x86_64 microVMs, ACPI will be the only way Firecracker passes hardware information to the guest once MPTable support is removed. : Added a check in the network TX path that the size of the network frames the guest passes to us is not bigger than the maximum frame the device expects to handle. On the TX path, we copy frames destined to MMDS from guest memory to Firecracker memory. Without the check, a mis-behaving virtio-net driver could cause an increase in the memory footprint of the Firecracker process. Now, if we receive such a frame, we ignore it and increase `Net::txmalformedframes` metric. : Make the first differential snapshot taken after a full snapshot contain only the set of memory pages changed since the full snapshot. Previously, these differential snapshots would contain all memory pages. This will result in potentially much smaller differential snapshots after a full snapshot. : Fix UFFD support not being forward-compatible with new ioctl options introduced in Linux 6.6. See also https://github.com/bytecodealliance/userfaultfd-rs/issues/61. : Added support to emit aggregate (minimum/maximum/sum) latency for `VcpuExit::MmioRead`, `VcpuExit::MmioWrite`, `VcpuExit::IoIn` and

The average for these VM exits is not emitted since it can be deduced from the available emitted metrics. : Added dev-preview support for backing a VM's guest memory by 2M hugetlbfs pages. Please see the for more information : Added block and net device metrics for file/tap access latencies and queue backlog lengths, which can be used to analyse saturation of the Firecracker VMM thread and underlying layers. Queue backlog length metrics are flushed periodically. They can be used to esimtate an average queue length by request by dividing its value by the number of requests served. : Changed microVM snapshot format version strategy. Firecracker snapshot format now has a version that is independent of Firecracker version. The current version of the snapshot format is v1.0.0. From now on, the Firecracker binary will define the snapshot format version it supports and it will only be able to load snapshots with format that is backwards compatible with that version. Users can pass the `--snapshot-version` flag to the Firecracker binary to see its supported snapshot version format. This change renders all previous Firecracker snapshots (up to Firecracker version v1.6.0) incompatible with the current Firecracker version. : Added information about page size to the payload Firecracker sends to the UFFD handler. Each memory region object now contains a `pagesizekib` field. See also the . : Only use memfd to back guest memory if a vhost-user-blk device is configured, otherwise use anonymous private memory. This is because serving page faults of shared memory used by memfd is slower and may impact workloads. : Fixed a bug in the cpu-template-helper that made it panic during conversion of cpu configuration with SVE registers to the cpu template on aarch64 platform. Now cpu-template-helper will print warnings if it encounters SVE registers during the conversion process. This is because cpu templates are limited to only modify registers less than 128 bits. : Fixed a bug in the Firecracker that prevented it to restore snapshots of VMs that had SVE enabled. : Made `PATCH` requests to the `/machine-config` endpoint transactional, meaning Firecracker's configuration will be unchanged if the request returns an error. This fixes a bug where a microVM with incompatible balloon and guest memory size could be booted, due to the check for this condition happening after Firecracker's configuration was updated. : Added a double fork mechanism in the Jailer to avoid setsid() failures occurred while running Jailer as the process group leader. However, this changed the behaviour of Jailer and now the Firecracker process will always have a different PID than the Jailer process. : Added a "Known Limitations" section in the Jailer docs to highlight the above change in behaviour introduced in PR#4259. : As a solution to the change in behaviour introduced in PR#4259, provided a mechanism to reliably fetch Firecracker PID. With this change, Firecracker process's PID will always be available in the Jailer's root directory regardless of whether newpidns was set. : Fixed a bug where a client would hang or timeout when querying for an MMDS path whose content is empty, because the 'Content-Length' header field was missing in a response. : Added support for per net device metrics. In addition to aggregate metrics `net`, each individual net device will emit metrics under the label `"net{ifaceid}"`. E.g. the associated metrics for the endpoint `"/network-interfaces/eth0"` will be available under `"net_eth0"` in the metrics json object. : Added support for per block device

In addition to aggregate metrics `block`, each individual block device will emit metrics under the label `"block{driveid}"`. E.g. the associated metrics for the endpoint `"/drives/{driveid}"` will be available under `"blockdrive_id"` in the metrics json object. : Added a new `vm-state` subcommand to `info-vmstate` command in the `snapshot-editor` tool to print MicrovmState of vmstate snapshot file in a readable format. Also made the `vcpu-states` subcommand available on x86_64. : Added source-level instrumentation based tracing. See for more details. , , , , : Added developer preview only (NOT for production use) support for vhost-user block devices. Firecracker implements a vhost-user frontend. Users are free to choose from existing open source backend solutions or their own implementation. Known limitation: snapshotting is not currently supported for microVMs containing vhost-user block devices. See the for details. The device emits metrics under the label `"vhostuser{device}{driveid}"`. : The jailer's option `--parent-cgroup` will move the process to that cgroup if no `cgroup` options are provided. Simplified and clarified the removal policy of deprecated API elements to follow semantic versioning 2.0.0. For more information, please refer to . : Refactored error propagation to avoid logging and printing an error on exits with a zero exit code. Now, on successful exit "Firecracker exited successfully" is logged. : Removed support for creating Firecracker snapshots targeting older versions of Firecracker. With this change, running 'firecracker --version' will not print the supported snapshot versions. : Allow merging of diff snapshots into base snapshots by directly writing the diff snapshot on top of the base snapshot's memory file. This can be done by setting the `memfilepath` to the path of the pre-existing full snapshot. : `rebase-snap` tool is now deprecated. Users should use `snapshot-editor` for rebasing diff snapshots. : Fixed a bug that ignored the `--show-log-origin` option, preventing it from printing the source code file of the log messages. : Fixed a bug reporting a non-zero exit code on successful shutdown when starting Firecracker with `--no-api`. : Fixed a bug where Firecracker would log "RunWithApiError error: MicroVMStopped without an error: GenericError" when exiting after encountering an emulation error. It now correctly prints "RunWithApiError error: MicroVMStopped with an error: GenericError". : Fixed a bug introduced in #4047 that limited the `--level` option of logger to Pascal-cased values (e.g. accepting "Info", but not "info"). It now ignores case again. : Fixed a bug in the asynchronous virtio-block engine that rendered the device non-functional after a PATCH request was issued to Firecracker for updating the path to the host-side backing file of the device. : Fixed a bug where if Firecracker was instructed to take a snapshot of a microvm which itself was restored from a snapshot, specifying `memfilepath` to be the path of the memory file from which the microvm was restored would result in both the microvm and the snapshot being corrupted. It now instead performs a "write-back" of all memory that was updated since the snapshot was originally loaded. : Added official support for Linux 6.1. See for some security and performance considerations. and : Added `snapshot-editor` tool for modifications of snapshot files. It allows for rebasing of memory snapshot files, printing and removing aarch64 registers from the vmstate and obtaining snapshot version. : Added new fields to the custom CPU templates. (aarch64 only) `vcpu_features` field allows modifications of vCPU features enabled during vCPU initialization. `kvm_capabilities` field allows modifications of KVM capability checks that Firecracker performs during boot. If any of these fields are in use, minimal target snapshot version is restricted to

Updated deserialization of `bitmap` for custom CPU templates to allow usage of '\_' as a separator. Changed the strip feature of `cpu-template-helper` tool to operate bitwise. Better logs during validation of CPU ID in snapshot restoration path. Also Firecracker now does not fail if it can't get CPU ID from the host or can't find CPU ID in the snapshot. Changed the serial device to only try to initialize itself if stdin is a terminal or a FIFO pipe. This fixes logged warnings about the serial device failing to initialize if the process is daemonized (in which case stdin is /dev/null instead of a terminal). Changed to show a warning message when launching a microVM with C3 template on a processor prior to Intel Cascade Lake, because the guest kernel does not apply the mitigation against MMIO stale data vulnerability when it is running on a processor that does not enumerate FBSDPNO, PSDPNO and SBDRSSDPNO on IA32ARCHCAPABILITIES MSR. Made Firecracker resize its file descriptor table on process start. It now preallocates the in-kernel fdtable to hold `RLIMIT_NOFILE` many fds (or 2048 if no limit is set). This avoids the kernel reallocating the fdtable during Firecracker operations, resulting in a 30ms to 70ms reduction of snapshot restore times for medium to large microVMs with many devices attached. Changed the dump feature of `cpu-template-helper` tool not to enumerate program counter (PC) on ARM because it is determined by the given kernel image and it is useless in the custom CPU template context. The ability to create snapshots for an older version of Firecracker is now deprecated. As a result, the `version` body field in `PUT` on `/snapshot/create` request in deprecated. Added support for the /dev/userfaultfd device available on linux kernels >= 6.1. This is the default for creating UFFD handlers on these kernel versions. If it is unavailable, Firecracker falls back to the userfaultfd syscall. Deprecated `cpu_template` field in `PUT` and `PATCH` requests on `/machine-config` API, which is used to set a static CPU template. Custom CPU templates added in v1.4.0 are available as an improved iteration of the static CPU templates. For more information about the transition from static CPU templates to custom CPU templates, please refer to . Changed default log level from to . This results in more logs being output by default. Fixed a change in behavior of normalize host brand string that breaks Firecracker on external instances. Fixed the T2A CPU template not to unset the MMX bit (CPUID.80000001h:EDX\[23\]) and the FXSR bit (CPUID.80000001h:EDX\[24\]). Fixed the T2A CPU template to set the RstrFpErrPtrs bit (CPUID.80000008h:EBX\[2\]). Fixed a bug where Firecracker would crash during boot if a guest set up a virtio queue that partially overlapped with the MMIO gap. Now Firecracker instead correctly refuses to activate the corresponding virtio device. Fixed the T2CL CPU template to pass through security mitigation bits that are listed by KVM as bits able to be passed through. By making the most use of the available hardware security mitigations on a processor that a guest is running on, the guest might be able to benefit from performance improvements. Fixed the T2S CPU template to set the GDSNO bit of the IA32ARCH_CAPABILITIES MSR to 1 in accordance with an Intel microcode update. To use the template securely, users should apply the latest microcode update on the host. Fixed the spelling of the `nomodule` param passed in the default kernel command line

This is a breaking change for setups that use the default kernel command line which also depend on being able to load kernel modules at runtime. This may also break setups which use the default kernel command line and which use an init binary that inadvertently depends on the misspelled param ("nomodules") being present at the command line, since this param will no longer be passed. Added support for custom CPU templates allowing users to adjust vCPU features exposed to the guest via CPUID, MSRs and ARM registers. Introduced V1N1 static CPU template for ARM to represent Neoverse V1 CPU as Neoverse N1. Added support for the `virtio-rng` entropy device. The device is optional. A single device can be enabled per VM using the `/entropy` endpoint. Added a `cpu-template-helper` tool for assisting with creating and managing custom CPU templates. Set FDPEXCPTNONLY bit (CPUID.7h.0:EBX\[6\]) and ZEROFCSFDS bit (CPUID.7h.0:EBX\[13\]) in Intel's CPUID normalization process. Fixed feature flags in T2S CPU template on Intel Ice Lake. Fixed CPUID leaf 0xb to be exposed to guests running on AMD host. Fixed a performance regression in the jailer logic for closing open file descriptors. Related to: . A race condition that has been identified between the API thread and the VMM thread due to a misconfiguration of the `apieventfd`. Fixed CPUID leaf 0x1 to disable perfmon and debug feature on x86 host. Fixed passing through cache information from host in CPUID leaf 0x80000006. Fixed the T2S CPU template to set the RRSBA bit of the IA32ARCHCAPABILITIES MSR to 1 in accordance with an Intel microcode update. Fixed the T2CL CPU template to pass through the RSBA and RRSBA bits of the IA32ARCHCAPABILITIES MSR from the host in accordance with an Intel microcode update. Fixed passing through cache information from host in CPUID leaf 0x80000005. Fixed the T2A CPU template to disable SVM (nested virtualization). Fixed the T2A CPU template to set EferLmsleUnsupported bit (CPUID.80000008h:EBX\[20\]), which indicates that EFER\[LMSLE\] is not supported. Introduced T2CL (Intel) and T2A (AMD) CPU templates to provide instruction set feature parity between Intel and AMD CPUs when using these templates. Added Graviton3 support (c7g instance type). Improved error message when invalid network backend provided. Improved TCP throughput by between 5% and 15% (depending on CPU) by using scatter-gather I/O in the net device's TX path. Upgraded Rust toolchain from 1.64.0 to 1.66.0. Made seccompiler output bit-reproducible. Fixed feature flags in T2 CPU template on Intel Ice Lake. Added a new CPU template called `T2S`. This exposes the same CPUID as `T2` to the Guest and also overwrites the `ARCH_CAPABILITIES` MSR to expose a reduced set of capabilities. With regards to hardware vulnerabilities and mitigations, the Guest vCPU will apear to look like a Skylake CPU, making it safe to snapshot uVMs running on a newer host CPU (Cascade Lake) and restore on a host that has a Skylake CPU. Added a new CLI option `--metrics-path PATH`. It accepts a file parameter where metrics will be sent to. Added baselines for m6i.metal and m6a.metal for all long running performance tests. Releases now include debuginfo files. Changed the jailer option `--exec-file` to fail if the filename does not contain the string `firecracker` to prevent from running non-firecracker binaries. Upgraded Rust toolchain from 1.52.1 to 1.64.0. Switched to specifying our dependencies using caret requirements instead of comparison requirements. Updated all dependencies to their respective newest

Made the `T2` template more robust by explicitly disabling additional CPUID flags that should be off but were missed initially or that were not available in the spec when the template was created. Now MAC address is correctly displayed when queried with GET `/vm/config` if left unspecified in both pre and post snapshot states. Fixed a self-DoS scenario in the virtio-queue code by reporting and terminating execution when the number of available descriptors reported by the driver is higher than the queue size. Fixed the bad handling of kernel cmdline parameters when init arguments were provided in the `boot_args` field of the JSON body of the PUT `/boot-source` request. Fixed a bug on ARM64 hosts where the upper 64bits of the V0-V31 FL/SIMD registers were not saved correctly when taking a snapshot, potentially leading to data loss. This change invalidates all ARM64 snapshots taken with versions of Firecracker \<= 1.1.3. Improved stability and security when saving CPU MSRs in snapshots. The API `PATCH` methods for `machine-config` can now be used to reset the `cpu_template` to `"None"`. Until this change there was no way to reset the `cpu_template` once it was set. Added a `rebase-snap` tool for rebasing a diff snapshot over a base snapshot. Mmds version is persisted across snapshot-restore. Snapshot compatibility is preserved bidirectionally, to and from a Firecracker version that does not support persisting the Mmds version. In such cases, the default V1 option is used. Added `--mmds-size-limit` for limiting the mmds data store size instead of piggy-backing on `--http-api-max-payload-size`. If left unconfigured it defaults to the value of `--http-api-max-payload-size`, to provide backwards compatibility. Added optional `mem_backend` body field in `PUT` requests on `/snapshot/load`. This new parameter is an object that defines the configuration of the backend responsible for handling memory loading during snapshot restore. The `membackend` parameter contains `backendtype` and `backend_path` required fields. `backend_type` is an enum that can take either `File` or `Uffd` as value. Interpretation of `backend_path` field depends on the value of `backend_type`. If `File`, then the user must provide the path to file that contains the guest memory to be loaded. Otherwise, if `backend_type` is `Uffd`, then `backend_path` is the path to a unix domain socket where a custom page fault handler process is listening and expecting a UFFD to be sent by Firecracker. The UFFD is used to handle the guest memory page faults in the separate process. Added logging for the snapshot/restore and async block device IO engine features to indicate they are in development preview. The API `PATCH` method for `/machine-config` can be now used to change `trackdirtypages` on aarch64. MmdsV2 is now Generally Available. MmdsV1 is now deprecated and will be removed in Firecracker v2.0.0. Use MmdsV2 instead. Deprecated `memfilepath` body field in `PUT` on `/snapshot/load` request. Fixed inconsistency that allowed the start of a microVM from a JSON file without specifying the `vcpucount` and `memsize_mib` parameters for `machine-config` although they are mandatory when configuring via the API. Now these fields are mandatory when specifying `machine-config` in the JSON file and when using the `PUT` request on `/machine-config`. Fixed inconsistency that allowed a user to specify the `cpu_template` parameter and set `smt` to `True` in `machine-config` when starting from a JSON file on aarch64 even though they are not permitted when using `PUT` or `PATCH` in the API. Now Firecracker will return an error on aarch64 if `smt` is set to `True` or if `cpu_template` is

Fixed inconsistent behaviour of the `PUT` method for `/machine-config` that would reset the `trackdirtypages` parameter to `false` if it was not specified in the JSON body of the request, but left the `cpu_template` parameter intact if it was not present in the request. Now a `PUT` request for `/machine-config` will reset all optional parameters (`smt`, `cpu_template`, `trackdirtypages`) to their default values if they are not specified in the `PUT` request. Fixed incosistency in the swagger definition with the current state of the `/vm/config` endpoint. Added jailer option `--parent-cgroup <relative_path>` to allow the placement of microvm cgroups in custom cgroup nested hierarchies. The default value is `<exec-file>` which is backwards compatible to the behavior before this change. Added jailer option `--cgroup-version <1|2>` to support running the jailer on systems that have cgroup-v2. Default value is `1` which means that if `--cgroup-version` is not specified, the jailer will try to create cgroups on cgroup-v1 hierarchies only. Added `--http-api-max-payload-size` parameter to configure the maximum payload size for PUT and PATCH requests. Limit MMDS data store size to `--http-api-max-payload-size`. Cleanup all environment variables in Jailer. Added metrics for accesses to deprecated HTTP and command line API endpoints. Added permanent HTTP endpoint for `GET` on `/version` for getting the Firecracker version. Added `--metadata` parameter to enable MMDS content to be supplied from a file allowing the MMDS to be used when using `--no-api` to disable the API server. Checksum file for the release assets. Added support for custom headers to MMDS requests. Accepted headers are: `X-metadata-token`, which accepts a string value that provides a session token for MMDS requests; and `X-metadata-token-ttl-seconds`, which specifies the lifetime of the session token in seconds. Support and validation for host and guest kernel 5.10. A . Added `io_engine` to the pre-boot block device configuration. Possible values: `Sync` (the default option) or `Async` (only available for kernels newer than 5.10.51). The `Async` variant introduces a block device engine that uses io_uring for executing requests asynchronously, which is in developer preview (NOT for production use). See `docs/api_requests/block-io-engine.md`. Added `block.ioenginethrottled_events` metric for measuring the number of virtio events throttled because of the IO engine. New optional `version` field to PUT requests towards `/mmds/config` to configure MMDS version. Accepted values are `V1` and `V2` and default is `V1`. MMDS `V2` is developer preview only (NOT for production use) and it does not currently work after snapshot load. Mandatory `network_interfaces` field to PUT requests towards `/mmds/config` which contains a list of network interface IDs capable of forwarding packets to MMDS. Removed the `--node` jailer parameter. Deprecated `vsock_id` body field in `PUT`s on `/vsock`. Removed the deprecated the `--seccomp-level parameter`. `GET` requests to MMDS require a session token to be provided through `X-metadata-token` header when using V2. Allow `PUT` requests to MMDS in order to generate a session token to be used for future `GET` requests when version 2 is used. Remove `allowmmdsrequests` field from the request body that attaches network interfaces. Specifying interfaces that allow forwarding requests to MMDS is done by adding the network interface's ID to the `network_interfaces` field of PUT `/mmds/config` request's body. Renamed `/machine-config` `ht_enabled` to `smt`. `smt` field is now optional on PUT `/machine-config`, defaulting to `false`. Configuring `smt: true` on aarch64 via the API is forbidden. GET `/vm/config` was returning a default config object after restoring from a snapshot. It now correctly returns the config of the original microVM, except for bootconfig and the cputemplate and smt fields of the machine config, which are currently lost. Fixed incorrect propagation of init parameters in kernel commandline. Related to: . Adapt T2 and C3 CPU templates for kernel

Firecracker was not previously masking some CPU features of the host or emulated by KVM, introduced in more recent kernels: `umip`, `vmx`, `avx512_vnni`. Fix jailer's cgroup implementation to accept properties that contain multiple dots. Added devtool build `--ssh-keys` flag to support fetching from private git repositories. Added option to configure block device flush. Added `--new-pid-ns` flag to the Jailer in order to spawn the Firecracker process in a new PID namespace. Added API metrics for `GET`, `PUT` and `PATCH` requests on `/mmds` endpoint. Added `--describe-snapshot` flag to Firecracker to fetch the data format version of a snapshot state file provided as argument. Added `--no-seccomp` parameter for disabling the default seccomp filters. Added `--seccomp-filter` parameter for supplying user-provided, custom filters. Added the `seccompiler-bin` binary that is used to compile JSON seccomp filters into serialized BPF for Firecracker consumption. Snapshotting support for GICv2 enabled guests. Added `devtool install` to deploy built binaries in `/usr/local/bin` or a given path. Added code logic to send `VIRTIOVSOCKEVENTTRANSPORTRESET` on snapshot creation, when the Vsock device is active. The event will close active connections on the guest. Added `GET` request on `/vm/config` that provides full microVM configuration as a JSON HTTP response. Added `--resource-limit` flag to jailer to limit resources such as: number of file descriptors allowed at a time (with a default value of 2048) and maximum size of files created by the process. Changed Docker images repository from DockerHub to Amazon ECR. Fixed off-by-one error in virtio-block descriptor address validation. Changed the `PATCH` request on `/balloon/statistics` to schedule the first statistics update immediately after processing the request. Deprecated the `--seccomp-level parameter`. It will be removed in a future release. Using it logs a runtime warning. Experimental gnu libc builds use empty default seccomp filters, allowing all system calls. Fixed non-compliant check for the RTC device ensuring a fixed 4-sized data buffer. Unnecessary interrupt assertion was removed from the RTC. However, a dummy interrupt is still allocated for snapshot compatibility reasons. Fixed the SIGPIPE signal handler so Firecracker no longer exits. The signal is still recorded in metrics and logs. Fixed ballooning API definitions by renaming all fields which mentioned "MB" to use "MiB" instead. Snapshot related host files (vm-state, memory, block backing files) are now flushed to their backing mediums as part of the CreateSnapshot operation. Fixed the SSBD mitigation not being enabled on `aarch64` with the provided `prod-host-setup.md`. Fixed the balloon statistics not working after a snapshot restore event. The `utctimestampms` now reports the timestamp in ms from the UTC UNIX Epoch, as the name suggests. It was previously using a monotonic clock with an undefined starting point. Added optional `resume_vm` field to `/snapshot/load` API call. Added support for block rate limiter PATCH. Added devtool test `-c|--cpuset-cpus` flag for cpus confinement when tests run. Added devtool test `-m|--cpuset-mems` flag for memory confinement when tests run. Added the virtio traditional memory ballooning device. Added a mechanism to handle vCPU/VMM errors that result in process termination. Added incremental guest memory snapshot support. Added aarch64 snapshot support. Change the information provided in `DescribeInstance` command to provide microVM state information (Not started/Running/Paused) instead of whether it's started or not. Removed the jailer `--extra-args` parameter. It was a noop, having been replaced by the `--` separator for extra arguments. Changed the output of the `--version` command line parameter to include a list of supported snapshot data format versions for the firecracker binary. Increased the maximum number of virtio devices from 11 to 19. Added a new check that prevents creating

snapshots when more than 11 devices are attached. If the stdout buffer is full and non-blocking, the serial writes no longer block. Any new bytes will be lost, until the buffer is freed. The device also logs these errors and increments the `uart.error_count` metric for each lost byte. Fixed inconsistency in YAML file InstanceInfo definition Added metric for throttled block device events. Added metrics for counting rate limiter throttling events. Added metric for counting MAC address updates. Added metrics for counting TAP read and write errors. Added metrics for counting RX and TX partial writes. Added metrics that measure the duration of pausing and resuming the microVM, from the VMM perspective. Added metric for measuring the duration of the last full/diff snapshot created, from the VMM perspective. Added metric for measuring the duration of loading a snapshot, from the VMM perspective. Added metrics that measure the duration of pausing and resuming the microVM, from the API (user) perspective. Added metric for measuring the duration of the last full/diff snapshot created, from the API (user) perspective. Added metric for measuring the duration of loading a snapshot, from the API (user) perspective. Added `trackdirtypages` field to `machine-config`. If enabled, Firecracker can create incremental guest memory snapshots by saving the dirty guest pages in a sparse file. Added a new API call, `PATCH /vm`, for changing the microVM state (to `Paused` or `Resumed`). Added a new API call, `PUT /snapshot/create`, for creating a full or diff snapshot. Added a new API call, `PUT /snapshot/load`, for loading a snapshot. Added new jailer command line argument `--cgroup` which allow the user to specify the cgroups that are going to be set by the Jailer. Added full support for AMD CPUs (General Availability). More details . Boot time on AMD achieves the desired performance (i.e under 150ms). The logger `level` field is now case-insensitive. Disabled boot timer device after restoring a snapshot. Enabled boot timer device only when specifically requested, by using the `--boot-timer` dedicated cmdline parameter. firecracker and jailer `--version` now gets updated on each devtool build to the output of `git describe --dirty`, if the git repo is available. MicroVM process is only attached to the cgroups defined by using `--cgroups` or the ones defined indirectly by using `--node`. Changed `devtool build` to build jailer binary for `musl` only targets. Building jailer binary for `non-musl` targets have been removed. Added a new API call, `PUT /metrics`, for configuring the metrics system. Added `app_name` field in InstanceInfo struct for storing the application name. New command-line parameters for `firecracker`, named `--log-path`, `--level`, `--show-level` and `--show-log-origin` that can be used for configuring the Logger when starting the process. When using this method for configuration, only `--log-path` is mandatory. Added a for updating the dev container image. Added a new API call, `PUT /mmds/config`, for configuring the `MMDS` with a custom valid link-local IPv4 address. Added experimental JSON response format support for MMDS guest applications requests. Added metrics for the vsock device. Added `devtool strip` command which removes debug symbols from the release binaries. Added the `txmalformedframes` metric for the virtio net device, emitted when a TX frame missing the VNET header is encountered. Added `--version` flag to both Firecracker and Jailer. Return `405 Method Not Allowed` MMDS response for non HTTP `GET` MMDS requests originating from guest. Fixed folder permissions in the jail (#1802). Any number of whitespace characters are accepted after ":" when parsing HTTP

Potential panic condition caused by the net device expecting to find a VNET header in every frame. Potential crash scenario caused by "Content-Length" HTTP header field accepting negative values. Fixed #1754 - net: traffic blocks when running ingress UDP performance tests with very large buffers. Updated CVE-2019-3016 mitigation information in In case of using an invalid JSON as a 'config-file' for Firecracker, the process will exit with return code 152. Removed the `testrun.sh` wrapper. Removed `metrics_fifo` field from the logger configuration. Renamed `logfifo` field from LoggerConfig to `logpath` and `metrics_fifo` field from MetricsConfig to `metrics_path`. `PATCH /drives/{id}` only allowed post-boot. Use `PUT` for pre-boot updates to existing configurations. `PATCH /network-interfaces/{id}` only allowed post-boot. Use `PUT` for pre-boot updates to existing configurations. Changed returned status code from `500 Internal Server Error` to `501 Not Implemented`, for queries on the MMDS endpoint in IMDS format, when the requested resource value type is unsupported. Allowed the MMDS data store to be initialized with all supported JSON types. Retrieval of these values within the guest, besides String, Array, and Dictionary, is only possible in JSON mode. `PATCH` request on `/mmds` before the data store is initialized returns `403 BadRequest`. Segregated MMDS documentation in MMDS design documentation and MMDS user guide documentation. Support for booting with an initial RAM disk image. This image can be specified through the new `initrd_path` field of the `/boot-source` API request. Fixed #1469 - Broken GitHub location for Firecracker release binary. The jailer allows changing the default api socket path by using the extra arguments passed to firecracker. Fixed #1456 - Occasional KVMEXITSHUTDOWN and bad syscall (14) during VM shutdown. Updated the production host setup guide with steps for addressing CVE-2019-18960. The HTTP header parsing is now case insensitive. The `putapirequests` and `patchapirequests` metrics for net devices were un-swapped. Removed redundant `--seccomp-level` jailer parameter since it can be simply forwarded to the Firecracker executable using "end of command options" convention. Removed `memory.dirty_pages` metric. Removed `options` field from the logger configuration. Decreased release binary size by ~15%. Changed default API socket path to `/run/firecracker.socket`. This path also applies when running with the jailer. Disabled KVM dirty page tracking by default. Removed redundant RescanBlockDevice action from the /actions API. The functionality is available through the PATCH /drives API. See `docs/api_requests/patch-block.md`. Added support for GICv2. Fixed CVE-2019-18960 - Fixed a logical error in bounds checking performed on vsock virtio descriptors. Fixed #1283 - Can't start a VM in AARCH64 with vcpus number more than 16. Fixed #1088 - The backtrace are printed on `panic`, no longer causing a seccomp fault. Fixed #1375 - Change logger options type from `Value` to `Vec<LogOption>` to prevent potential unwrap on None panics. Fixed #1436 - Raise interrupt for TX queue used descriptors Fixed #1439 - Prevent achieving 100% cpu load when the net device rx is throttled by the ratelimiter Fixed #1437 - Invalid fields in rate limiter related API requests are now failing with a proper error message. Fixed #1316 - correctly determine the size of a virtio device backed by a block device. Fixed #1383 - Log failed api requests. Decreased release binary size by 10%. New command-line parameter for `firecracker`, named `--no-api`, which will disable the API server thread. If set, the user won't be able to send any API requests, neither before, nor after the vm has booted. It must be paired with `--config-file` parameter. Also, when API server is disabled, MMDS is no longer available

New command-line parameter for `firecracker`, named `--config-file`, which represents the path to a file that contains a JSON which can be used for configuring and starting a microVM without sending any API requests. The jailer adheres to the "end of command options" convention, meaning all parameters specified after `--` are forwarded verbatim to Firecracker. Added `KVM_PTP` support to the recommended guest kernel config. Added entry in FAQ.md for Firecracker Guest timekeeping. Vsock API call: `PUT /vsocks/{id}` changed to `PUT /vsock` and no longer appear to support multiple vsock devices. Any subsequent calls to this API endpoint will override the previous vsock device configuration. Removed unused 'Halting' and 'Halted' instance states. Vsock host-initiated connections now implement a trivial handshake protocol. See the for details. Related to: , , Fixed serial console on aarch64 (GitHub issue #1147). Upon panic, the terminal is now reset to canonical mode. Explicit error upon failure of vsock device creation. The failure message returned by an API call is flushed in the log FIFOs. Insert virtio devices in the FDT in order of their addresses sorted from low to high. Enforce the maximum length of the network interface name to be 16 chars as specified in the Linux Kernel. Changed the vsock property `id` to `vsock_id` so that the API client can be successfully generated from the swagger definition. New device: virtio-vsock, backed by Unix domain sockets (GitHub issue #650). See `docs/vsock.md`. No error is thrown upon a flush metrics intent if logger has not been configured. Updated the documentation for integration tests. Fixed high CPU usage before guest network interface is brought up (GitHub issue #1049). Fixed an issue that caused the wrong date (month) to appear in the log. Fixed a bug that caused the seccomp filter to reject legit syscalls in some rare cases (GitHub issue #1206). Docs: updated the production host setup guide. Docs: updated the rootfs and kernel creation guide. Removed experimental support for vhost-based vsock devices. New API call: `PATCH /machine-config/`, used to update VM configuration, before the microVM boots. Added an experimental swagger definition that includes the specification for the vsock API call. Added a signal handler for `SIGBUS` and `SIGSEGV` that immediately terminates the process upon intercepting the signal. Added documentation for signal handling utilities. Added \[alpha\] aarch64 support. Added metrics for successful read and write operations of MMDS, Net and Block devices. `vcpucount`, `memsizemib` and `htenabled` have been changed to be mandatory for `PUT` requests on `/machine-config/`. Disallow invalid seccomp levels by exiting with error. Incorrect handling of bind mounts within the jailed rootfs. Corrected the guide for `Alpine` guest setup. Added \[alpha\] AMD support. New `devtool` command: `prepare_release`. This updates the Firecracker version, crate dependencies and credits in preparation for a new release. New `devtool` command: `tag`. This creates a new git tag for the specified release number, based on the changelog contents. New doc section about building with glibc. Dropped the JSON-formatted `context` command-line parameter from Firecracker in favor of individual classic command-line parameters. When running with `jailer` the location of the API socket has changed to `<jail-root-path>/api.socket` (API socket was moved inside the jail). `PUT` and `PATCH` requests on `/mmds` with data containing any value type other than `String`, `Array`, `Object` will returns status code 400. Improved multiple error messages. Removed all kernel modules from the recommended kernel config. Corrected the seccomp filter when building with glibc. Removed the `seccomp.bad_syscalls` metric. Corrected the conditional compilation of the seccomp rule for

A `madvise` call issued by the `musl` allocator was added to the seccomp allow list to prevent Firecracker from terminating abruptly when allocating memory in certain conditions. New API action: SendCtrlAltDel, used to initiate a graceful shutdown, if the guest has driver support for i8042 and AT Keyboard. See for details. New metric counting the number of egress packets with a spoofed MAC: `net.txspoofedmac_count`. New API call: `PATCH /network-interfaces/`, used to update the rate limiters on a network interface, after the start of a microVM. Added missing `vmm_version` field to the InstanceInfo API swagger definition, and marked several other mandatory fields as such. New default command line for guest kernel: `reboot=k panic=1 pci=off nomodules 8250.nr_uarts=0 i8042.noaux i8042.nomux i8042.nopnp i8042.dumbkbd`. virtio-blk: VIRTIOBLKT_FLUSH now working as expected. Vsock devices can be attached when starting Firecracker using the jailer. Vsock devices work properly when seccomp filtering is enabled. Documentation for development environment setup on AWS in `dev-machine-setup.md`. Documentation for microVM networking setup in `docs/network-setup.md`. Limit the maximum supported vCPUs to 32. Log the app version when the `Logger` is initialized. Pretty print panic information. Firecracker terminates with exit code 148 when a syscall which is not present in the allow list is intercepted. Fixed build with the `vsock` feature. Documentation for Logger API Requests in `docs/api_requests/logger.md`. Documentation for Actions API Requests in `docs/api_requests/actions.md`. Documentation for MMDS in `docs/mmds.md`. Flush metrics on request via a PUT `/actions` with the `action_type` field set to `FlushMetrics`. Updated the swagger definition of the `Logger` to specify the required fields and provide default values for optional fields. Default `seccomp-level` is `2` (was previously 0). API Resource IDs can only contain alphanumeric characters and underscores. Seccomp filters are now applied to all Firecracker threads. Enforce minimum length of 1 character for the jailer ID. Exit with error code when starting the jailer process fails. Removed `InstanceHalt` from the list of possible actions. The `/logger` API has a new field called `options`. This is an array of strings that specify additional logging configurations. The only supported value is `LogDirtyPages`. When the `LogDirtyPages` option is configured via `PUT /logger`, a new metric called `memory.dirty_pages` is computed as the number of pages dirtied by the guest since the last time the metric was flushed. Log messages on both graceful and forceful termination. Availability of the list of dependencies for each commit inside the code base. Documentation on vsock experimental feature and host setup recommendations. `PUT` requests on `/mmds` always return 204 on success. `PUT` operations on `/network-interfaces` API resources no longer accept the previously required `state` parameter. The jailer starts with `--seccomp-level=2` (was previously 0) by default. Log messages use `anonymous-instance` as instance id if none is specified. Fixed crash upon instance start on hosts without 1GB huge page support. Fixed "fault_message" inconsistency between Open API specification and code base. Ensure MMDS compatibility with C5's IMDS implementation. Corrected the swagger specification to ensure `OpenAPI 2.0` compatibility. Apache-2.0 license Docs: - - - Experimental vhost-based vsock implementation. Improved MMDS network stack performance. If the logging system is not yet initialized (via `PUT /logger`), log events are now sent to stdout/stderr. Moved the `instanceinfofails` metric under `getapirequests` Improved and added links to more detailed information, now featured in subject-specific docs. Fixed bug in the MMDS network stack, that caused some RST packets to be sent without a destination. Fixed bug in `PATCH /drives`, whereby the ID in the path was not checked against the ID in the body. The Swagger definition was corrected. Each Firecracker process has an associated microVM Metadata Store

Its contents can be configured using the `/mmds` API resource. The boot source is specified only with the `kernelimagepath` and the optional parameter `boot_args`. All other fields are removed. The `pathonhost` property in the drive specification is now marked as mandatory. PATCH drive only allows patching/changing the `pathonhost` property. All PUT and PATCH requests return the status code 204. CPUID brand string (aka model name) now includes the host CPU frequency. API requests which add guest network interfaces have an additional parameter, `allowmmdsrequests` which defaults to `false`. Stopping the guest (e.g. using the `reboot` command) also terminates the Firecracker process. When the Firecracker process ends for any reason, (other than `kill -9`), metrics are flushed at the very end. On startup `jailer` closes all inherited file descriptors based on `sysconf(SCOPEN_MAX)` except input, output and error. The microVM ID prefixes each Firecracker log line. This ID also appears in the process `cmdline` so it's now possible to `ps | grep <ID>` for it. Seccomp filtering is configured via the `--seccomp-level` jailer parameter. Firecracker logs the starting addresses of host memory areas provided as guest memory slots to KVM. The metric `panic_count` gets incremented to signal that a panic has occurred. Firecracker logs a backtrace when it crashes following a panic. Added basic instrumentation support for measuring boot time. `StartInstance` is a synchronous API request (it used to be an asynchronous request). Ensure that fault messages sent by the API have valid JSON bodies. Use HTTP response code 500 for internal Firecracker errors, and 400 for user errors on InstanceStart. Serialize the machine configuration fields to the correct data types (as specified in the Swagger definition). NUMA node assignment is properly enforced by the jailer. The `isrootdevice` and `isreadonly` properties are now marked as required in the Swagger definition of `Drive` object properties. `GET` requests on the `/actions` API resource are no longer supported. The metrics associated with asynchronous actions have been removed. Remove the `action_id` parameter for `InstanceStart`, both from the URI and the JSON request body. The jailer can now be configured to enter a preexisting network namespace, and to run as a daemon. Enabled PATCH operations on `/drives` resources. The microVM `id` supplied to the jailer may now contain alphanumeric characters and hyphens, up to a maximum length of 64 characters. Replaced the `permissions` property of `/drives` resources with a boolean. Removed the `state` property of `/drives` resources. Rate limiting functionality allows specifying an initial one time burst size. Firecracker can now boot from an arbitrary boot partition by specifying its unique id in the driver's API call. Block device rescan is triggered via a PUT `/actions` with the drive ID in the action body's `payload` field and the `action_type` field set to `BlockDeviceRescan`. Removed `noapic` from the default guest kernel command line. The `action_id` parameter is no longer required for synchronous PUT requests to `/actions`. PUT requests are no longer allowed on `/drives` resources after the guest has booted. Fixed guest instance kernel loader to accelerate vCPUs launch and consequently guest kernel boot. Fixed network emulation to improve IO performance. Firecracker uses two different named pipes to record human readable logs and metrics, respectively. Seccomp filtering can be enabled via setting the `USE_SECCOMP` environment variable. It is possible to supply only a partial specification when attaching a rate limiter (i.e. just the bandwidth or ops parameter). Errors related to guest network interfaces are now more

Fixed a bug that was causing Firecracker to panic whenever a `PUT` request was sent on an existing network interface. The `id` parameter of the `jailer` is required to be an RFC 4122-compliant UUID. Fixed an issue which caused the network RX rate limiter to be more restrictive than intended. API requests which contain unknown fields will generate an error. Fixed an issue related to high CPU utilization caused by improper `KVM PIT` configuration. It is now possible to create more than one network tun/tap interface inside a jailed Firecracker. Added metrics for API requests, VCPU and device actions for the serial console (`UART`), keyboard (`i8042`), block and network devices. Metrics are logged every 60 seconds. A CPU features template for C3 is available, in addition to the one for T2. Seccomp filters restrict Firecracker from calling any other system calls than the minimum set it needs to function properly. The filters are enabled by setting the `USE_SECCOMP` environment variable to 1 before running Firecracker. Firecracker can be started by a new binary called `jailer`. The jailer takes as command line arguments a unique ID, the path to the Firecracker binary, the NUMA node that Firecracker will be assigned to and a `uid` and `gid` for Firecracker to run under. It sets up a `chroot` environment and a `cgroup`, and calls exec to morph into Firecracker. In case of failure, the metrics and the panic location are logged before aborting. Metric values are reset with every flush. `CPUTemplate` is now called `CpuTemplate` in order to work seamlessly with the swagger code generator for Go. `firecracker-beta.yaml` is now called `firecracker.yaml`. Handling was added for several untreated KVM exit scenarios, which could have led to panic. Fixed a bug that caused Firecracker to crash when attempting to disable the `IA32DEBUGINTERFACE MSR` flag in the T2 CPU features. Removed a leftover file generated by the logger unit tests. Removed `firecracker-v1.0.yaml`. The CPU Template can be set with an API call on `PUT /machine-config`. The only available template is T2. Hyperthreading can be enabled/disabled with an API call on `PUT /machine-config`. By default, hyperthreading is disabled. Added boot time performance test (`tests/performance/test_boottime.py`). Added Rate Limiter for VirtIO/net and VirtIO/net devices. The Rate Limiter uses two token buckets to limit rate on bytes/s and ops/s. The rate limiter can be (optionally) configured per drive with a `PUT` on `/drives/{drive_id}` and per network interface with a `PUT` on `/network-interface/{iface_id}`. Implemented pre-boot PUT updates for `/boot-source`, `/drives`, `/network-interfaces` and `/vsock`. Added integration tests for `PUT` updates. Moved the API definition (`swagger/firecracker-beta.yaml`) to the `api_server` crate. Removed `"console=ttyS0"` and added `"8250.nr_uarts=0"` to the default kernel command line to decrease the boot time. Changed the CPU topology to have all logical CPUs on a single socket. Removed the upper bound on CPU count as with musl there is no good way to get the total number of logical processors on a host. Build time tests now print the full output of commands. Disabled the Performance Monitor Unit and the Turbo Boost. Check the expected KVM capabilities before starting the VM. Logs now have timestamps. `testrun.sh` can run on platforms with more than one package manager by setting the package manager via a command line parameter (`-p`). Allow correct set up of multiple network-interfaces with auto-generated MAC. Fixed sporadic bug in VirtIO which was causing lost packages. Don't allow `PUT` requests with empty body on `/machine-config`. Deny `PUT` operations after the microvm boots (exception: the temporarily fix for live resize of block

Removed examples crate. This used to have a Python example of starting Firecracker. This is replaced by `test_api.py` integration tests. Removed helper scripts for getting coverage and coding style errors. These were replaced by `testcoverage.py` and `teststyle.py` test integration tests. Removed `--vmm-no-api` command line option. Firecracker can only be started via the API. Users can interrogate the Machine Configuration (i.e. vcpu count and memory size) using a `GET` request on `/machine-config`. The logging system can be configured through the API using a `PUT` on `/logger`. Block devices support live resize by calling `PUT` with the same parameters as when the block was created. Release builds have Link Time Optimization (LTO) enabled. Firecracker is built with `musl`, resulting in a statically linked binary. More in-tree integration tests were added as part of the continuous integration system. The vcpu count is enforced to `1` or an even number. The Swagger definition of rate limiters was updated. Syslog-enabled logs were replaced with a host-file backed mechanism. The host topology of the CPU and the caches is not leaked into the microvm anymore. Boot time was improved by advertising the availability of the TSC deadline timer. Fixed an issue which prevented Firecracker from working on 4.14 (or newer) host kernels. Specifying the MAC address for an interface through the API is optional. Removed support for attaching vsock devices. Removed support for building Firecracker with glibc. Users can now interrogate Instance Information (currently just instance state) through the API. Renamed `api/swagger/all.yaml` to `api/swagger/firecracker-v1.0.yaml` which specifies targeted API support for Firecracker v1.0. Renamed `api/swagger/firecracker-v0.1.yaml` to `api/swagger/firecracker-beta.yaml` which specifies the currently supported API. Users can now enforce that an emulated block device is read-only via the API. To specify whether a block device is read-only or read-write, an extra "permissions" field was added to the Drive definition in the API. The root filesystem is automatically mounted in the guest OS as `ro`/`rw` according to the specified "permissions". It's the responsibility of the user to mount any other read-only block device as such within the guest OS. Users can now stop the guest VM using the API. Actions of type `InstanceHalt` are now supported via the API. Added support for `getDeviceID()` in `virtIO-block`. Without this, the guest Linux kernel would complain at boot time that the operation is unsupported. `stdin` control is returned to the Firecracker process when guest VM is inactive. Raw mode `stdin` is forwarded to the guest OS when guest VM is running. Removed `api/swagger/actions.yaml`. Removed `api/swagger/devices.yaml`. Removed `api/swagger/firecracker-mvp.yaml`. Removed `api/swagger/limiters.yaml`. Users can now specify the MAC address of a guest network interface via the `PUT` network interface API request. Previously, the guest MAC address parameter was ignored. Fixed a guest memory allocation issue, which previously led to a potentially significant memory chunk being wasted. Fixed an issue which caused compilation problems, due to a compatibility breaking transitive dependency in the tokio suite of crates. One-process virtual machine manager (one Firecracker per microVM). RESTful API running on a unix socket. The API supported by v0.1 can be found at `api/swagger/firecracker-v0.1.yaml`. Emulated keyboard (`i8042`) and serial console (`UART`). The microVM serial console input and output are connected to those of the Firecracker process (this allows direct console access to the guest OS). The capability of mapping an existing host tun-tap device as a VirtIO/net device into the microVM. The capability of mapping an existing host file as a GirtIO/block device into the microVM. The capability of creating a VirtIO/vsock between the host and the microVM. Default demand fault paging & CPU oversubscription.