Chapter 2. Recommended performance and scalability practices 2.1. Recommended control plane practices This topic provides recommended performance and scalability practices for control planes in OpenShift Container Platform. 2.1.1. Recommended practices for scaling the cluster The guidance in this section is only relevant for installations with cloud provider integration. Apply the following best practices to scale the number of worker machines in your OpenShift Container Platform cluster. You scale the worker machines by increasing or decreasing the number of replicas that are defined in the worker machine set. When scaling up the cluster to higher node counts: Spread nodes across all of the available zones for higher availability. Scale up by no more than 25 to 50 machines at once. Consider creating new compute machine sets in each available zone with alternative instance types of similar size to help mitigate any periodic provider capacity constraints. For example, on AWS, use m5.large and m5d.large. Note Cloud providers might implement a quota for API services. Therefore, gradually scale the cluster. The controller might not be able to create the machines if the replicas in the compute machine sets are set to higher numbers all at one time. The number of requests the cloud platform, which OpenShift Container Platform is deployed on top of, is able to handle impacts the process. The controller will start to query more while trying to create, check, and update the machines with the status. The cloud platform on which OpenShift Container Platform is deployed has API request limits; excessive queries might lead to machine creation failures due to cloud platform limitations. Enable machine health checks when scaling to large node counts. In case of failures, the health checks monitor the condition and automatically repair unhealthy machines. Note When scaling large and dense clusters to lower node counts, it might take large amounts of time because the process involves draining or evicting the objects running on the nodes being terminated in parallel. Also, the client might start to throttle the requests if there are too many objects to evict. The default client queries per second (QPS) and burst rates are currently set to 50 and 100 respectively. These values cannot be modified in OpenShift Container Platform. 2.1.2. Control plane node sizing The control plane node resource requirements depend on the number and type of nodes and objects in the cluster. The following control plane node size recommendations are based on the results of a control plane density focused testing, or Cluster-density . This test creates the following objects across a given number of namespaces: 1 image stream 1 build 5 deployments, with 2 pod replicas in a sleep state, mounting 4 secrets, 4 config maps, and 1 downward API volume each 5 services, each one pointing to the TCP/8080 and TCP/8443 ports of one of the deployments 1 route pointing to the first of the services 10 secrets containing 2048 random string characters 10 config maps containing 2048 random string characters Number of worker nodes Cluster-density (namespaces) CPU cores Memory (GB) 24 500 4 16 120 1000 8 32 252 4000 16, but 24 if using the OVN-Kubernetes network plug-in 64, but 128 if using the OVN-Kubernetes network plug-in 501, but untested with the OVN-Kubernetes network plug-in 4000 16 96 The data from the table above is based on an OpenShift Container Platform running on top of AWS, using r5.4xlarge instances as control-plane nodes and m5.2xlarge instances as worker nodes. On a large and dense cluster with three control plane nodes, the CPU and memory usage will spike up when one of the nodes is stopped, rebooted, or fails. The failures can be due to unexpected issues with power, network, underlying infrastructure, or intentional cases where the cluster is restarted after shutting it down to save costs. The remaining two control plane nodes must handle the load in order to be highly available, which leads to increase in the resource usage. This is also expected during upgrades because the control plane nodes are cordoned, drained, and rebooted serially to apply the operating system updates, as well as the control plane Operators update. To avoid cascading failures, keep the overall CPU and memory resource usage on the control plane nodes to at most 60% of all available capacity to handle the resource usage spikes. Increase the CPU and memory on the control plane nodes accordingly to avoid potential downtime due to lack of resources. Important The node sizing varies depending on the number of nodes and object counts in the cluster. It also depends on whether the objects are actively being created on the cluster. During object creation, the control plane is more active in terms of resource usage compared to when the objects are in the running phase. Operator Lifecycle Manager (OLM ) runs on the control plane nodes and its memory footprint depends on the number of namespaces and user installed operators that OLM needs to manage on the cluster. Control plane nodes need to be sized accordingly to avoid OOM kills. Following data points are based on the results from cluster maximums testing. Number of namespaces OLM memory at idle state (GB) OLM memory with 5 user operators installed (GB) 500 0.823 1.7 1000 1.2 2.5 1500 1.7 3.2 2000 2 4.4 3000 2.7 5.6 4000 3.8 7.6 5000 4.2 9.02 6000 5.8 11.3 7000 6.6 12.9 8000 6.9 14.8 9000 8 17.7 10,000 9.9 21.6 Important You can modify the control plane node size in a running OpenShift Container Platform 4.15 cluster for the following configurations only: Clusters installed with a user-provisioned installation method. AWS clusters installed with an installer-provisioned infrastructure installation method. Clusters that use a control plane machine set to manage control plane machines. For all other configurations, you must estimate your total node count and use the suggested control plane node size during installation. Important The recommendations are based on the data points captured on OpenShift Container Platform clusters with OpenShift SDN as the network plugin. Note In OpenShift Container Platform 4.15, half of a CPU core (500 millicore) is now reserved by the system by default compared to OpenShift Container Platform 3.11 and versions. The sizes are determined taking that into consideration. 2.1.2.1. Selecting a larger Amazon Web Services instance type for control plane machines If the control plane machines in an Amazon Web Services (AWS) cluster require more resources, you can select a larger AWS instance type for the control plane machines to use. Note The procedure for clusters that use a control plane machine set is different from the procedure for clusters that do not use a control plane machine set. If you are uncertain about the state of the ControlPlaneMachineSet CR in your cluster, you can verify the CR status . 2.1.2.1.1. Changing the Amazon Web Services instance type by using a control plane machine set You can change the Amazon Web Services (AWS) instance type that your control plane machines use by updating the specification in the control plane machine set custom resource (CR). Prerequisites Your AWS cluster uses a control plane machine set. Procedure Edit your control plane machine set CR by running the following command: USD oc --namespace openshift-machine-api edit controlplanemachineset.machine.openshift.io cluster Edit the following line under the providerSpec field: providerSpec: value: ... instanceType: <compatible_aws_instance_type> 1 1 Specify a larger AWS instance type with the same base as the selection. For example, you can change m6i.xlarge to m6i.2xlarge or m6i.4xlarge . Save your changes. For clusters that use the default RollingUpdate update strategy, the Operator automatically propagates the changes to your control plane configuration. For clusters that are configured to use the OnDelete update strategy, you must replace your control plane machines manually. Additional resources Managing control plane machines with control plane machine sets 2.1.2.1.2. Changing the Amazon Web Services instance type by using the AWS console You can change the Amazon Web Services (AWS) instance type that your control plane machines use by updating the instance type in the AWS console. Prerequisites You have access to the AWS console with the permissions required to modify the EC2 Instance for your cluster. You have access to the OpenShift Container Platform cluster as a user with the cluster-admin role. Procedure Open the AWS console and fetch the instances for the control plane machines. Choose one control plane machine instance. For the selected control plane machine, back up the etcd data by creating an etcd snapshot. For more information, see "Backing up etcd". In the AWS console, stop the control plane machine instance. Select the stopped instance, and click Actions Instance Settings Change instance type . Change the instance to a larger type, ensuring that the type is the same base as the selection, and apply changes. For example, you can change m6i.xlarge to m6i.2xlarge or m6i.4xlarge . Start the instance. If your OpenShift Container Platform cluster has a corresponding Machine object for the instance, update the instance type of the object to match the instance type set in the AWS console. Repeat this process for each control plane machine. Additional resources Backing up etcd AWS documentation about changing the instance type 2.2. Recommended infrastructure practices This topic provides recommended performance and scalability practices for infrastructure in OpenShift Container Platform. 2.2.1. Infrastructure node sizing Infrastructure nodes are nodes that are labeled to run pieces of the OpenShift Container Platform environment. The infrastructure node resource requirements depend on the cluster age, nodes, and objects in the cluster, as these factors can lead to an increase in the number of metrics or time series in Prometheus. The following infrastructure node size recommendations are based on the results observed in cluster-density testing detailed in the Control plane node sizing section, where the monitoring stack and the default ingress-controller were moved to these nodes. Number of worker nodes Cluster density, or number of namespaces CPU cores Memory (GB) 27 500 4 24 120 1000 8 48 252 4000 16 128 501 4000 32 128 In general, three infrastructure nodes are recommended per cluster. Important These sizing recommendations should be used as a guideline. Prometheus is a highly memory intensive application; the resource usage depends on various factors including the number of nodes, objects, the Prometheus metrics scraping interval, metrics or time series, and the age of the cluster. In addition, the router resource usage can also be affected by the number of routes and the amount/type of inbound requests. These recommendations apply only to infrastructure nodes hosting Monitoring, Ingress and Registry infrastructure components installed during cluster creation. Note In OpenShift Container Platform 4.15, half of a CPU core (500 millicore) is now reserved by the system by default compared to OpenShift Container Platform 3.11 and versions. This influences the stated sizing recommendations. 2.2.2. Scaling the Cluster Monitoring Operator OpenShift Container Platform exposes metrics that the Cluster Monitoring Operator (CMO) collects and stores in the Prometheus-based monitoring stack. As an administrator, you can view dashboards for system resources, containers, and components metrics in the OpenShift Container Platform web console by navigating to Observe Dashboards . 2.2.3. Prometheus database storage requirements Red Hat performed various tests for different scale sizes. Note The following Prometheus storage requirements are not prescriptive and should be used as a reference. Higher resource consumption might be observed in your cluster depending on workload activity and resource density, including the number of pods, containers, routes, or other resources exposing metrics collected by Prometheus. You can configure the size-based data retention policy to suit your storage requirements. Table 2.1. Prometheus Database storage requirements based on number of nodes/pods in the cluster Number of nodes Number of pods (2 containers per pod) Prometheus storage growth per day Prometheus storage growth per 15 days Network (per tsdb chunk) 50 1800 6.3 GB 94 GB 16 MB 100 3600 13 GB 195 GB 26 MB 150 5400 19 GB 283 GB 36 MB 200 7200 25 GB 375 GB 46 MB Approximately 20 percent of the expected size was added as overhead to ensure that the storage requirements do not exceed the calculated value. The above calculation is for the default OpenShift Container Platform Cluster Monitoring Operator. Note CPU utilization has minor impact. The ratio is approximately 1 core out of 40 per 50 nodes and 1800 pods. Recommendations for OpenShift Container Platform Use at least two infrastructure (infra) nodes. Use at least three openshift-container-storage nodes with non-volatile memory express (SSD or NVMe) drives. 2.2.4. Configuring cluster monitoring You can increase the storage capacity for the Prometheus component in the cluster monitoring stack. Procedure To increase the storage capacity for Prometheus: Create a YAML configuration file, cluster-monitoring-config.yaml . For example: apiVersion: v1 kind: ConfigMap data: config.yaml: | prometheusK8s: retention: {{PROMETHEUS_RETENTION_PERIOD}} 1 nodeSelector: node-role.kubernetes.io/infra: "" volumeClaimTemplate: spec: storageClassName: {{STORAGE_CLASS}} 2 resources: requests: storage: {{PROMETHEUS_STORAGE_SIZE}} 3 alertmanagerMain: nodeSelector: node-role.kubernetes.io/infra: "" volumeClaimTemplate: spec: storageClassName: {{STORAGE_CLASS}} 4 resources: requests: storage: {{ALERTMANAGER_STORAGE_SIZE}} 5 metadata: name: cluster-monitoring-config namespace: openshift-monitoring 1 The default value of Prometheus retention is PROMETHEUS_RETENTION_PERIOD=15d . Units are measured in time using one of these suffixes: s, m, h, d. 2 4 The storage class for your cluster. 3 A typical value is PROMETHEUS_STORAGE_SIZE=2000Gi . Storage values can be a plain integer or a fixed-point integer using one of these suffixes: E, P, T, G, M, K. You can also use the power-of-two equivalents: Ei, Pi, Ti, Gi, Mi, Ki. 5 A typical value is ALERTMANAGER_STORAGE_SIZE=20Gi . Storage values can be a plain integer or a fixed-point integer using one of these suffixes: E, P, T, G, M, K. You can also use the power-of-two equivalents: Ei, Pi, Ti, Gi, Mi, Ki. Add values for the retention period, storage class, and storage sizes. Save the file. Apply the changes by running: USD oc create -f cluster-monitoring-config.yaml 2.2.5. Additional resources Infrastructure Nodes in OpenShift 4 OpenShift Container Platform cluster maximums Creating infrastructure machine sets 2.3. Recommended etcd practices This topic provides recommended performance and scalability practices for etcd in OpenShift Container Platform. 2.3.1. Recommended etcd practices Because etcd writes data to disk and persists proposals on disk, its performance depends on disk performance. Although etcd is not particularly I/O intensive, it requires a low latency block device for optimal performance and stability. Because etcd's consensus protocol depends on persistently storing metadata to a log (WAL), etcd is sensitive to disk-write latency. Slow disks and disk activity from other processes can cause long fsync latencies. Those latencies can cause etcd to miss heartbeats, not commit new proposals to the disk on time, and ultimately experience request timeouts and temporary leader loss. High write latencies also lead to an OpenShift API slowness, which affects cluster performance. Because of these reasons, avoid colocating other workloads on the control-plane nodes that are I/O sensitive or intensive and share the same underlying I/O infrastructure. In terms of latency, run etcd on top of a block device that can write at least 50 IOPS of 8000 bytes long sequentially. That is, with a latency of 10ms, keep in mind that uses fdatasync to synchronize each write in the WAL. For heavy loaded clusters, sequential 500 IOPS of 8000 bytes (2 ms) are recommended. To measure those numbers, you can use a benchmarking tool, such as fio. To achieve such performance, run etcd on machines that are backed by SSD or NVMe disks with low latency and high throughput. Consider single-level cell (SLC) solid-state drives (SSDs), which provide 1 bit per memory cell, are durable and reliable, and are ideal for write-intensive workloads. Note The load on etcd arises from static factors, such as the number of nodes and pods, and dynamic factors, including changes in endpoints due to pod autoscaling, pod restarts, job executions, and other workload-related events. To accurately size your etcd setup, you must analyze the specific requirements of your workload. Consider the number of nodes, pods, and other relevant factors that impact the load on etcd. The following hard drive practices provide optimal etcd performance: Use dedicated etcd drives. Avoid drives that communicate over the network, such as iSCSI. Do not place log files or other heavy workloads on etcd drives. Prefer drives with low latency to support fast read and write operations. Prefer high-bandwidth writes for faster compactions and defragmentation. Prefer high-bandwidth reads for faster recovery from failures. Use solid state drives as a minimum selection. Prefer NVMe drives for production environments. Use server-grade hardware for increased reliability. Note Avoid NAS or SAN setups and spinning drives. Ceph Rados Block Device (RBD) and other types of network-attached storage can result in unpredictable network latency. To provide fast storage to etcd nodes at scale, use PCI passthrough to pass NVM devices directly to the nodes. Always benchmark by using utilities such as fio. You can use such utilities to continuously monitor the cluster performance as it increases. Note Avoid using the Network File System (NFS) protocol or other network based file systems. Some key metrics to monitor on a deployed OpenShift Container Platform cluster are p99 of etcd disk write ahead log duration and the number of etcd leader changes. Use Prometheus to track these metrics. Note The etcd member database sizes can vary in a cluster during normal operations. This difference does not affect cluster upgrades, even if the leader size is different from the other members. To validate the hardware for etcd before or after you create the OpenShift Container Platform cluster, you can use fio. Prerequisites Container runtimes such as Podman or Docker are installed on the machine that you're testing. Data is written to the /var/lib/etcd path. Procedure Run fio and analyze the results: If you use Podman, run this command: USD sudo podman run --volume /var/lib/etcd:/var/lib/etcd:Z quay.io/cloud-bulldozer/etcd-perf If you use Docker, run this command: USD sudo docker run --volume /var/lib/etcd:/var/lib/etcd:Z quay.io/cloud-bulldozer/etcd-perf The output reports whether the disk is fast enough to host etcd by comparing the 99th percentile of the fsync metric captured from the run to see if it is less than 10 ms. A few of the most important etcd metrics that might affected by I/O performance are as follow: etcd_disk_wal_fsync_duration_seconds_bucket metric reports the etcd's WAL fsync duration etcd_disk_backend_commit_duration_seconds_bucket metric reports the etcd backend commit latency duration etcd_server_leader_changes_seen_total metric reports the leader changes Because etcd replicates the requests among all the members, its performance strongly depends on network input/output (I/O) latency. High network latencies result in etcd heartbeats taking longer than the election timeout, which results in leader elections that are disruptive to the cluster. A key metric to monitor on a deployed OpenShift Container Platform cluster is the 99th percentile of etcd network peer latency on each etcd cluster member. Use Prometheus to track the metric. The histogram_quantile(0.99, rate(etcd_network_peer_round_trip_time_seconds_bucket[2m])) metric reports the round trip time for etcd to finish replicating the client requests between the members. Ensure that it is less than 50 ms. Additional resources How to use fio to check etcd disk performance in OpenShift Container Platform etcd performance troubleshooting guide for OpenShift Container Platform 2.3.2. Moving etcd to a different disk You can move etcd from a shared disk to a separate disk to prevent or resolve performance issues. The Machine Config Operator (MCO) is responsible for mounting a secondary disk for OpenShift Container Platform 4.15 container storage. Note This encoded script only supports device names for the following device types: SCSI or SATA /dev/sd* Virtual device /dev/vd* NVMe /dev/nvme*[0-9]*n* Limitations When the new disk is attached to the cluster, the etcd database is part of the root mount. It is not part of the secondary disk or the intended disk when the primary node is recreated. As a result, the primary node will not create a separate /var/lib/etcd mount. Prerequisites You have a backup of your cluster's etcd data. You have installed the OpenShift CLI ( oc ). You have access to the cluster with cluster-admin privileges. Add additional disks before uploading the machine configuration. The MachineConfigPool must match metadata.labels[machineconfiguration.openshift.io/role] . This applies to a controller, worker, or a custom pool. Note This procedure does not move parts of the root file system, such as /var/ , to another disk or partition on an installed node. Important This procedure is not supported when using control plane machine sets. Procedure Attach the new disk to the cluster and verify that the disk is detected in the node by running the lsblk command in a debug shell: USD oc debug node/<node_name> # lsblk Note the device name of the new disk reported by the lsblk command. Create the following script and name it etcd-find-secondary-device.sh : #!/bin/bash set -uo pipefail for device in <device_type_glob>; do 1 /usr/sbin/blkid "USD{device}" &> /dev/null if [ USD? == 2 ]; then echo "secondary device found USD{device}" echo "creating filesystem for etcd mount" mkfs.xfs -L var-lib-etcd -f "USD{device}" &> /dev/null udevadm settle touch /etc/var-lib-etcd-mount exit fi done echo "Couldn't find secondary block device!" >&2 exit 77 1 Replace <device_type_glob> with a shell glob for your block device type. For SCSI or SATA drives, use /dev/sd* ; for virtual drives, use /dev/vd* ; for NVMe drives, use /dev/nvme*[0-9]*n* . Create a base64-encoded string from the etcd-find-secondary-device.sh script and note its contents: USD base64 -w0 etcd-find-secondary-device.sh Create a MachineConfig YAML file named etcd-mc.yml with contents such as the following: apiVersion: machineconfiguration.openshift.io/v1 kind: MachineConfig metadata: labels: machineconfiguration.openshift.io/role: master name: 98-var-lib-etcd spec: config: ignition: version: 3.4.0 storage: files: - path: /etc/find-secondary-device mode: 0755 contents: source: data:text/plain;charset=utf-8;base64,<encoded_etcd_find_secondary_device_script> 1 systemd: units: - name: find-secondary-device.service enabled: true contents: | [Unit] Description=Find secondary device DefaultDependencies=false After=systemd-udev-settle.service Before=local-fs-pre.target ConditionPathExists=!/etc/var-lib-etcd-mount [Service] RemainAfterExit=yes ExecStart=/etc/find-secondary-device RestartForceExitStatus=77 [Install] WantedBy=multi-user.target - name: var-lib-etcd.mount enabled: true contents: | [Unit] Before=local-fs.target [Mount] What=/dev/disk/by-label/var-lib-etcd Where=/var/lib/etcd Type=xfs TimeoutSec=120s [Install] RequiredBy=local-fs.target - name: sync-var-lib-etcd-to-etcd.service enabled: true contents: | [Unit] Description=Sync etcd data if new mount is empty DefaultDependencies=no After=var-lib-etcd.mount var.mount Before=crio.service [Service] Type=oneshot RemainAfterExit=yes ExecCondition=/usr/bin/test ! -d /var/lib/etcd/member ExecStart=/usr/sbin/setsebool -P rsync_full_access 1 ExecStart=/bin/rsync -ar /sysroot/ostree/deploy/rhcos/var/lib/etcd/ /var/lib/etcd/ ExecStart=/usr/sbin/semanage fcontext -a -t container_var_lib_t '/var/lib/etcd(/.*)?' ExecStart=/usr/sbin/setsebool -P rsync_full_access 0 TimeoutSec=0 [Install] WantedBy=multi-user.target graphical.target - name: restorecon-var-lib-etcd.service enabled: true contents: | [Unit] Description=Restore recursive SELinux security contexts DefaultDependencies=no After=var-lib-etcd.mount Before=crio.service [Service] Type=oneshot RemainAfterExit=yes ExecStart=/sbin/restorecon -R /var/lib/etcd/ TimeoutSec=0 [Install] WantedBy=multi-user.target graphical.target 1 Replace <encoded_etcd_find_secondary_device_script> with the encoded script contents that you noted. Verification steps Run the grep /var/lib/etcd /proc/mounts command in a debug shell for the node to ensure that the disk is mounted: USD oc debug node/<node_name> # grep -w "/var/lib/etcd" /proc/mounts Example output /dev/sdb /var/lib/etcd xfs rw,seclabel,relatime,attr2,inode64,logbufs=8,logbsize=32k,noquota 0 0 Additional resources Red Hat Enterprise Linux CoreOS (RHCOS) 2.3.3. Defragmenting etcd data For large and dense clusters, etcd can suffer from poor performance if the keyspace grows too large and exceeds the space quota. Periodically maintain and defragment etcd to free up space in the data store. Monitor Prometheus for etcd metrics and defragment it when required; otherwise, etcd can raise a cluster-wide alarm that puts the cluster into a maintenance mode that accepts only key reads and deletes. Monitor these key metrics: etcd_server_quota_backend_bytes , which is the current quota limit etcd_mvcc_db_total_size_in_use_in_bytes , which indicates the actual database usage after a history compaction etcd_mvcc_db_total_size_in_bytes , which shows the database size, including free space waiting for defragmentation Defragment etcd data to reclaim disk space after events that cause disk fragmentation, such as etcd history compaction. History compaction is performed automatically every five minutes and leaves gaps in the back-end database. This fragmented space is available for use by etcd, but is not available to the host file system. You must defragment etcd to make this space available to the host file system. Defragmentation occurs automatically, but you can also trigger it manually. Note Automatic defragmentation is good for most cases, because the etcd operator uses cluster information to determine the most efficient operation for the user. 2.3.3.1. Automatic defragmentation The etcd Operator automatically defragments disks. No manual intervention is needed. Verify that the defragmentation process is successful by viewing one of these logs: etcd logs cluster-etcd-operator pod operator status error log Warning Automatic defragmentation can cause leader election failure in various OpenShift core components, such as the Kubernetes controller manager, which triggers a restart of the failing component. The restart is harmless and either triggers failover to the running instance or the component resumes work again after the restart. Example log output for successful defragmentation etcd member has been defragmented: <member_name> , memberID: <member_id> Example log output for unsuccessful defragmentation failed defrag on member: <member_name> , memberID: <member_id> : <error_message> 2.3.3.2. Manual defragmentation A Prometheus alert indicates when you need to use manual defragmentation. The alert is displayed in two cases: When etcd uses more than 50% of its available space for more than 10 minutes When etcd is actively using less than 50% of its total database size for more than 10 minutes You can also determine whether defragmentation is needed by checking the etcd database size in MB that will be freed by defragmentation with the PromQL expression: (etcd_mvcc_db_total_size_in_bytes - etcd_mvcc_db_total_size_in_use_in_bytes)/1024/1024 Warning Defragmenting etcd is a blocking action. The etcd member will not respond until defragmentation is complete. For this reason, wait at least one minute between defragmentation actions on each of the pods to allow the cluster to recover. Follow this procedure to defragment etcd data on each etcd member. Prerequisites You have access to the cluster as a user with the cluster-admin role. Procedure Determine which etcd member is the leader, because the leader should be defragmented last. Get the list of etcd pods: USD oc -n openshift-etcd get pods -l k8s-app=etcd -o wide Example output etcd-ip-10-0-159-225.example.redhat.com 3/3 Running 0 175m 10.0.159.225 ip-10-0-159-225.example.redhat.com <none> <none> etcd-ip-10-0-191-37.example.redhat.com 3/3 Running 0 173m 10.0.191.37 ip-10-0-191-37.example.redhat.com <none> <none> etcd-ip-10-0-199-170.example.redhat.com 3/3 Running 0 176m 10.0.199.170 ip-10-0-199-170.example.redhat.com <none> <none> Choose a pod and run the following command to determine which etcd member is the leader: USD oc rsh -n openshift-etcd etcd-ip-10-0-159-225.example.redhat.com etcdctl endpoint status --cluster -w table Example output Defaulting container name to etcdctl. Use 'oc describe pod/etcd-ip-10-0-159-225.example.redhat.com -n openshift-etcd' to see all of the containers in this pod. +---------------------------+------------------+---------+---------+-----------+------------+-----------+------------+--------------------+--------+ | ENDPOINT | ID | VERSION | DB SIZE | IS LEADER | IS LEARNER | RAFT TERM | RAFT INDEX | RAFT APPLIED INDEX | ERRORS | +---------------------------+------------------+---------+---------+-----------+------------+-----------+------------+--------------------+--------+ | https://10.0.191.37:2379 | 251cd44483d811c3 | 3.5.9 | 104 MB | false | false | 7 | 91624 | 91624 | | | https://10.0.159.225:2379 | 264c7c58ecbdabee | 3.5.9 | 104 MB | false | false | 7 | 91624 | 91624 | | | https://10.0.199.170:2379 | 9ac311f93915cc79 | 3.5.9 | 104 MB | true | false | 7 | 91624 | 91624 | | +---------------------------+------------------+---------+---------+-----------+------------+-----------+------------+--------------------+--------+ Based on the IS LEADER column of this output, the https://10.0.199.170:2379 endpoint is the leader. Matching this endpoint with the output of the step, the pod name of the leader is etcd-ip-10-0-199-170.example.redhat.com . Defragment an etcd member. Connect to the running etcd container, passing in the name of a pod that is not the leader: USD oc rsh -n openshift-etcd etcd-ip-10-0-159-225.example.redhat.com Unset the ETCDCTL_ENDPOINTS environment variable: sh-4.4# unset ETCDCTL_ENDPOINTS Defragment the etcd member: sh-4.4# etcdctl --command-timeout=30s --endpoints=https://localhost:2379 defrag Example output Finished defragmenting etcd member[https://localhost:2379] If a timeout error occurs, increase the value for --command-timeout until the command succeeds. Verify that the database size was reduced: sh-4.4# etcdctl endpoint status -w table --cluster Example output +---------------------------+------------------+---------+---------+-----------+------------+-----------+------------+--------------------+--------+ | ENDPOINT | ID | VERSION | DB SIZE | IS LEADER | IS LEARNER | RAFT TERM | RAFT INDEX | RAFT APPLIED INDEX | ERRORS | +---------------------------+------------------+---------+---------+-----------+------------+-----------+------------+--------------------+--------+ | https://10.0.191.37:2379 | 251cd44483d811c3 | 3.5.9 | 104 MB | false | false | 7 | 91624 | 91624 | | | https://10.0.159.225:2379 | 264c7c58ecbdabee | 3.5.9 | 41 MB | false | false | 7 | 91624 | 91624 | | 1 | https://10.0.199.170:2379 | 9ac311f93915cc79 | 3.5.9 | 104 MB | true | false | 7 | 91624 | 91624 | | +---------------------------+------------------+---------+---------+-----------+------------+-----------+------------+--------------------+--------+ This example shows that the database size for this etcd member is now 41 MB as opposed to the starting size of 104 MB. Repeat these steps to connect to each of the other etcd members and defragment them. Always defragment the leader last. Wait at least one minute between defragmentation actions to allow the etcd pod to recover. Until the etcd pod recovers, the etcd member will not respond. If any NOSPACE alarms were triggered due to the space quota being exceeded, clear them. Check if there are any NOSPACE alarms: sh-4.4# etcdctl alarm list Example output memberID:12345678912345678912 alarm:NOSPACE Clear the alarms: sh-4.4# etcdctl alarm disarm 2.3.4. Setting tuning parameters for etcd You can set the control plane hardware speed to "Standard" , "Slower" , or the default, which is "" . The default setting allows the system to decide which speed to use. This value enables upgrades from versions where this feature does not exist, as the system can select values from versions. By selecting one of the other values, you are overriding the default. If you see many leader elections due to timeouts or missed heartbeats and your system is set to "" or "Standard" , set the hardware speed to "Slower" to make the system more tolerant to the increased latency. Important Tuning etcd latency tolerances is a Technology Preview feature only. Technology Preview features are not supported with Red Hat production service level agreements (SLAs) and might not be functionally complete. Red Hat does not recommend using them in production. These features provide early access to upcoming product features, enabling customers to test functionality and provide feedback during the development process. For more information about the support scope of Red Hat Technology Preview features, see Technology Preview Features Support Scope . 2.3.4.1. Changing hardware speed tolerance To change the hardware speed tolerance for etcd, complete the following steps. Prerequisites You have edited the cluster instance to enable TechPreviewNoUpgrade features. For more information, see "Understanding feature gates" in the Additional resources . Procedure Check to see what the current value is by entering the following command: USD oc describe etcd/cluster | grep "Control Plane Hardware Speed" Example output Control Plane Hardware Speed: <VALUE> Note If the output is empty, the field has not been set and should be considered as the default (""). Change the value by entering the following command. Replace <value> with one of the valid values: "" , "Standard" , or "Slower" : USD oc patch etcd/cluster --type=merge -p '{"spec": {"controlPlaneHardwareSpeed": "<value>"}}' The following table indicates the heartbeat interval and leader election timeout for each profile. These values are subject to change. Profile ETCD_HEARTBEAT_INTERVAL ETCD_LEADER_ELECTION_TIMEOUT "" Varies depending on platform Varies depending on platform Standard 100 1000 Slower 500 2500 Review the output: Example output etcd.operator.openshift.io/cluster patched If you enter any value besides the valid values, error output is displayed. For example, if you entered "Faster" as the value, the output is as follows: Example output The Etcd "cluster" is invalid: spec.controlPlaneHardwareSpeed: Unsupported value: "Faster": supported values: "", "Standard", "Slower" Verify that the value was changed by entering the following command: USD oc describe etcd/cluster | grep "Control Plane Hardware Speed" Example output Control Plane Hardware Speed: "" Wait for etcd pods to roll out: USD oc get pods -n openshift-etcd -w The following output shows the expected entries for master-0. Before you continue, wait until all masters show a status of 4/4 Running . Example output installer-9-ci-ln-qkgs94t-72292-9clnd-master-0 0/1 Pending 0 0s installer-9-ci-ln-qkgs94t-72292-9clnd-master-0 0/1 Pending 0 0s installer-9-ci-ln-qkgs94t-72292-9clnd-master-0 0/1 ContainerCreating 0 0s installer-9-ci-ln-qkgs94t-72292-9clnd-master-0 0/1 ContainerCreating 0 1s installer-9-ci-ln-qkgs94t-72292-9clnd-master-0 1/1 Running 0 2s installer-9-ci-ln-qkgs94t-72292-9clnd-master-0 0/1 Completed 0 34s installer-9-ci-ln-qkgs94t-72292-9clnd-master-0 0/1 Completed 0 36s installer-9-ci-ln-qkgs94t-72292-9clnd-master-0 0/1 Completed 0 36s etcd-guard-ci-ln-qkgs94t-72292-9clnd-master-0 0/1 Running 0 26m etcd-ci-ln-qkgs94t-72292-9clnd-master-0 4/4 Terminating 0 11m etcd-ci-ln-qkgs94t-72292-9clnd-master-0 4/4 Terminating 0 11m etcd-ci-ln-qkgs94t-72292-9clnd-master-0 0/4 Pending 0 0s etcd-ci-ln-qkgs94t-72292-9clnd-master-0 0/4 Init:1/3 0 1s etcd-ci-ln-qkgs94t-72292-9clnd-master-0 0/4 Init:2/3 0 2s etcd-ci-ln-qkgs94t-72292-9clnd-master-0 0/4 PodInitializing 0 3s etcd-ci-ln-qkgs94t-72292-9clnd-master-0 3/4 Running 0 4s etcd-guard-ci-ln-qkgs94t-72292-9clnd-master-0 1/1 Running 0 26m etcd-ci-ln-qkgs94t-72292-9clnd-master-0 3/4 Running 0 20s etcd-ci-ln-qkgs94t-72292-9clnd-master-0 4/4 Running 0 20s Enter the following command to review to the values: USD oc describe -n openshift-etcd pod/<ETCD_PODNAME> | grep -e HEARTBEAT_INTERVAL -e ELECTION_TIMEOUT Note These values might not have changed from the default. Additional resources Understanding feature gates

Commands:
oc --namespace openshift-machine-api edit controlplanemachineset.machine.openshift.io cluster
providerSpec: value: instanceType: <compatible_aws_instance_type> 1
apiVersion: v1 kind: ConfigMap data: config.yaml: | prometheusK8s: retention: {{PROMETHEUS_RETENTION_PERIOD}} 1 nodeSelector: node-role.kubernetes.io/infra: "" volumeClaimTemplate: spec: storageClassName: {{STORAGE_CLASS}} 2 resources: requests: storage: {{PROMETHEUS_STORAGE_SIZE}} 3 alertmanagerMain: nodeSelector: node-role.kubernetes.io/infra: "" volumeClaimTemplate: spec: storageClassName: {{STORAGE_CLASS}} 4 resources: requests: storage: {{ALERTMANAGER_STORAGE_SIZE}} 5 metadata: name: cluster-monitoring-config namespace: openshift-monitoring
oc create -f cluster-monitoring-config.yaml
sudo podman run --volume /var/lib/etcd:/var/lib/etcd:Z quay.io/cloud-bulldozer/etcd-perf
sudo docker run --volume /var/lib/etcd:/var/lib/etcd:Z quay.io/cloud-bulldozer/etcd-perf
oc debug node/<node_name>
lsblk
#!/bin/bash set -uo pipefail for device in <device_type_glob>; do 1 /usr/sbin/blkid "USD{device}" &> /dev/null if [ USD? == 2 ]; then echo "secondary device found USD{device}" echo "creating filesystem for etcd mount" mkfs.xfs -L var-lib-etcd -f "USD{device}" &> /dev/null udevadm settle touch /etc/var-lib-etcd-mount exit fi done echo "Couldn't find secondary block device!" >&2 exit 77
base64 -w0 etcd-find-secondary-device.sh
apiVersion: machineconfiguration.openshift.io/v1 kind: MachineConfig metadata: labels: machineconfiguration.openshift.io/role: master name: 98-var-lib-etcd spec: config: ignition: version: 3.4.0 storage: files: - path: /etc/find-secondary-device mode: 0755 contents: source: data:text/plain;charset=utf-8;base64,<encoded_etcd_find_secondary_device_script> 1 systemd: units: - name: find-secondary-device.service enabled: true contents: | [Unit] Description=Find secondary device DefaultDependencies=false After=systemd-udev-settle.service Before=local-fs-pre.target ConditionPathExists=!/etc/var-lib-etcd-mount [Service] RemainAfterExit=yes ExecStart=/etc/find-secondary-device RestartForceExitStatus=77 [Install] WantedBy=multi-user.target - name: var-lib-etcd.mount enabled: true contents: | [Unit] Before=local-fs.target [Mount] What=/dev/disk/by-label/var-lib-etcd Where=/var/lib/etcd Type=xfs TimeoutSec=120s [Install] RequiredBy=local-fs.target - name: sync-var-lib-etcd-to-etcd.service enabled: true contents: | [Unit] Description=Sync etcd data if new mount is empty DefaultDependencies=no After=var-lib-etcd.mount var.mount Before=crio.service [Service] Type=oneshot RemainAfterExit=yes ExecCondition=/usr/bin/test ! -d /var/lib/etcd/member ExecStart=/usr/sbin/setsebool -P rsync_full_access 1 ExecStart=/bin/rsync -ar /sysroot/ostree/deploy/rhcos/var/lib/etcd/ /var/lib/etcd/ ExecStart=/usr/sbin/semanage fcontext -a -t container_var_lib_t '/var/lib/etcd(/.*)?' ExecStart=/usr/sbin/setsebool -P rsync_full_access 0 TimeoutSec=0 [Install] WantedBy=multi-user.target graphical.target - name: restorecon-var-lib-etcd.service enabled: true contents: | [Unit] Description=Restore recursive SELinux security contexts DefaultDependencies=no After=var-lib-etcd.mount Before=crio.service [Service] Type=oneshot RemainAfterExit=yes ExecStart=/sbin/restorecon -R /var/lib/etcd/ TimeoutSec=0 [Install] WantedBy=multi-user.target graphical.target
oc debug node/<node_name>
grep -w "/var/lib/etcd" /proc/mounts
/dev/sdb /var/lib/etcd xfs rw,seclabel,relatime,attr2,inode64,logbufs=8,logbsize=32k,noquota 0 0
etcd member has been defragmented: <member_name> , memberID: <member_id>
failed defrag on member: <member_name> , memberID: <member_id> : <error_message>
oc -n openshift-etcd get pods -l k8s-app=etcd -o wide
etcd-ip-10-0-159-225.example.redhat.com 3/3 Running 0 175m 10.0.159.225 ip-10-0-159-225.example.redhat.com <none> <none> etcd-ip-10-0-191-37.example.redhat.com 3/3 Running 0 173m 10.0.191.37 ip-10-0-191-37.example.redhat.com <none> <none> etcd-ip-10-0-199-170.example.redhat.com 3/3 Running 0 176m 10.0.199.170 ip-10-0-199-170.example.redhat.com <none> <none>
oc rsh -n openshift-etcd etcd-ip-10-0-159-225.example.redhat.com etcdctl endpoint status --cluster -w table
Defaulting container name to etcdctl. Use 'oc describe pod/etcd-ip-10-0-159-225.example.redhat.com -n openshift-etcd' to see all of the containers in this pod. +---------------------------+------------------+---------+---------+-----------+------------+-----------+------------+--------------------+--------+ | ENDPOINT | ID | VERSION | DB SIZE | IS LEADER | IS LEARNER | RAFT TERM | RAFT INDEX | RAFT APPLIED INDEX | ERRORS | +---------------------------+------------------+---------+---------+-----------+------------+-----------+------------+--------------------+--------+ | https://10.0.191.37:2379 | 251cd44483d811c3 | 3.5.9 | 104 MB | false | false | 7 | 91624 | 91624 | | | https://10.0.159.225:2379 | 264c7c58ecbdabee | 3.5.9 | 104 MB | false | false | 7 | 91624 | 91624 | | | https://10.0.199.170:2379 | 9ac311f93915cc79 | 3.5.9 | 104 MB | true | false | 7 | 91624 | 91624 | | +---------------------------+------------------+---------+---------+-----------+------------+-----------+------------+--------------------+--------+
oc rsh -n openshift-etcd etcd-ip-10-0-159-225.example.redhat.com
sh-4.4# unset ETCDCTL_ENDPOINTS
sh-4.4# etcdctl --command-timeout=30s --endpoints=https://localhost:2379 defrag
Finished defragmenting etcd member[https://localhost:2379]
sh-4.4# etcdctl endpoint status -w table --cluster
+---------------------------+------------------+---------+---------+-----------+------------+-----------+------------+--------------------+--------+ | ENDPOINT | ID | VERSION | DB SIZE | IS LEADER | IS LEARNER | RAFT TERM | RAFT INDEX | RAFT APPLIED INDEX | ERRORS | +---------------------------+------------------+---------+---------+-----------+------------+-----------+------------+--------------------+--------+ | https://10.0.191.37:2379 | 251cd44483d811c3 | 3.5.9 | 104 MB | false | false | 7 | 91624 | 91624 | | | https://10.0.159.225:2379 | 264c7c58ecbdabee | 3.5.9 | 41 MB | false | false | 7 | 91624 | 91624 | | 1 | https://10.0.199.170:2379 | 9ac311f93915cc79 | 3.5.9 | 104 MB | true | false | 7 | 91624 | 91624 | | +---------------------------+------------------+---------+---------+-----------+------------+-----------+------------+--------------------+--------+
sh-4.4# etcdctl alarm list
memberID:12345678912345678912 alarm:NOSPACE
sh-4.4# etcdctl alarm disarm
oc describe etcd/cluster | grep "Control Plane Hardware Speed"
Control Plane Hardware Speed: <VALUE>
oc patch etcd/cluster --type=merge -p '{"spec": {"controlPlaneHardwareSpeed": "<value>"}}'
etcd.operator.openshift.io/cluster patched
The Etcd "cluster" is invalid: spec.controlPlaneHardwareSpeed: Unsupported value: "Faster": supported values: "", "Standard", "Slower"
oc describe etcd/cluster | grep "Control Plane Hardware Speed"
Control Plane Hardware Speed: ""
oc get pods -n openshift-etcd -w
installer-9-ci-ln-qkgs94t-72292-9clnd-master-0 0/1 Pending 0 0s installer-9-ci-ln-qkgs94t-72292-9clnd-master-0 0/1 Pending 0 0s installer-9-ci-ln-qkgs94t-72292-9clnd-master-0 0/1 ContainerCreating 0 0s installer-9-ci-ln-qkgs94t-72292-9clnd-master-0 0/1 ContainerCreating 0 1s installer-9-ci-ln-qkgs94t-72292-9clnd-master-0 1/1 Running 0 2s installer-9-ci-ln-qkgs94t-72292-9clnd-master-0 0/1 Completed 0 34s installer-9-ci-ln-qkgs94t-72292-9clnd-master-0 0/1 Completed 0 36s installer-9-ci-ln-qkgs94t-72292-9clnd-master-0 0/1 Completed 0 36s etcd-guard-ci-ln-qkgs94t-72292-9clnd-master-0 0/1 Running 0 26m etcd-ci-ln-qkgs94t-72292-9clnd-master-0 4/4 Terminating 0 11m etcd-ci-ln-qkgs94t-72292-9clnd-master-0 4/4 Terminating 0 11m etcd-ci-ln-qkgs94t-72292-9clnd-master-0 0/4 Pending 0 0s etcd-ci-ln-qkgs94t-72292-9clnd-master-0 0/4 Init:1/3 0 1s etcd-ci-ln-qkgs94t-72292-9clnd-master-0 0/4 Init:2/3 0 2s etcd-ci-ln-qkgs94t-72292-9clnd-master-0 0/4 PodInitializing 0 3s etcd-ci-ln-qkgs94t-72292-9clnd-master-0 3/4 Running 0 4s etcd-guard-ci-ln-qkgs94t-72292-9clnd-master-0 1/1 Running 0 26m etcd-ci-ln-qkgs94t-72292-9clnd-master-0 3/4 Running 0 20s etcd-ci-ln-qkgs94t-72292-9clnd-master-0 4/4 Running 0 20s
oc describe -n openshift-etcd pod/<ETCD_PODNAME> | grep -e HEARTBEAT_INTERVAL -e ELECTION_TIMEOUT