Project: containerd (Runtime / Container Runtime)
File: NRI.md

NRI, the Node Resource Interface, is a common framework for plugging extensions into OCI-compatible container runtimes. It provides basic mechanisms for plugins to track the state of containers and to make limited changes to their configuration. NRI itself is agnostic to the internal implementation details of any container runtime. It provides an adaptation library which runtimes use to integrate to and interact with NRI and plugins. In principle any NRI plugin should be able to work with NRI-enabled runtimes. For a detailed description of NRI and its capabilities please take a look at the . <details> <summary>see the containerd/NRI integration diagram</summary> <img src="./containerd-nri-integration.png" title="Containerd/NRI Integration"> </details> NRI support in containerd is split into two parts both logically and physically. These parts are a common plugin (/nri/*) to integrate to NRI and CRI-specific bits (/pkg/cri/server/nri-api) which convert data between the runtime-agnostic NRI representation and the internal representation of the CRI plugin. The containerd common NRI plugin implements the core logic of integrating to and interacting with NRI. However, it does this without any knowledge about the internal representation of containers or pods within containerd. It defines an additional interface, Domain, which is used whenever the internal representation of a container or pod needs to be translated to the runtime agnostic NRI one, or when a configuration change requested by an external NRI plugin needs to be applied to a container within containerd. `Domain` can be considered as a short-cut name for Domain-Namespace as Domain implements the functions the generic NRI interface needs to deal with pods and containers from a particular containerd namespace. As a reminder, containerd namespaces isolate state between clients of containerd. E.g. "k8s.io" for the kubernetes CRI clients, "moby" for docker clients, ... and "containerd" as the default for containerd/ctr. The containerd CRI plugin registers itself as an above mentioned NRI Domain for the "k8s.io" namespace, to allow container configuration to be customized by external NRI plugins. Currently this Domain interface is only implemented for the original CRI `pkg/cri/server` implementation. Implementing it for the more recent experimental `pkg/cri/sbserver` implementation is on the TODO list. The main reason for this split of functionality is to allow NRI plugins for other types of sandboxes and for other container clients other than just for CRI containers in the "k8s.io" namespace. Enabling and disabling NRI support in containerd happens by enabling or disabling the common containerd NRI plugin. Starting with containerd

The plugin, and consequently NRI functionality, is enabled by default. It can be disabled by editing the `[plugins."io.containerd.nri.v1.nri"]` section in the containerd configuration file, which by default is `/etc/containerd/config.toml`, and changing `disable = false` to `disable = true`. The NRI section to disable NRI functionality should look something like this: ```toml [plugins."io.containerd.nri.v1.nri"] disable = true disable_connections = false pluginconfigpath = "/etc/nri/conf.d" plugin_path = "/opt/nri/plugins" pluginregistrationtimeout = "5s" pluginrequesttimeout = "2s" socket_path = "/var/run/nri/nri.sock" ``` There are two ways how an NRI plugin can be started. Plugins can be pre-registered in which case they are automatically started when the NRI adaptation is instantiated (or in our case when containerd is started). Plugins can also be started by external means, for instance by systemd. Pre-registering a plugin happens by placing a symbolic link to the plugin executable into a well-known NRI-specific directory, `/opt/nri/plugins` by default. A pre-registered plugin is started with a socket pre-connected to NRI. Externally launched plugins connect to a well-known NRI-specific socket, `/var/run/nri/nri.sock` by default, to register themselves. The only difference between pre-registered and externally launched plugins is how they get started and connected to NRI. Once a connection is established all plugins are identical. NRI can be configured to disable connections from externally launched plugins, in which case the well-known socket is not created at all. The configuration fragment shown above ensures that external connections are enabled regardless of the built-in NRI defaults. This is convenient for testing as it allows one to connect, disconnect and reconnect plugins at any time. Note that you can't run two NRI-enabled runtimes on a single node with the same default socket configuration. You need to either disable NRI or change the NRI socket path in one of the runtimes. You can verify that NRI integration is properly enabled and functional by configuring containerd and NRI as described above, taking the NRI logger plugin from the on github, compiling it and starting it up. ```bash git clone https://github.com/containerd/nri cd nri make ./build/bin/logger -idx 00 ``` You should see the logger plugin receiving receiving a list of existing pods and containers. If you then create or remove further pods and containers using crictl or kubectl you should see detailed logs of the corresponding NRI events printed by the logger. You can enable backward compatibility with NRI v0.1.0 plugins using the . ```bash git clone https://github.com/containerd/nri cd nri make sudo cp build/bin/v010-adapter /usr/local/bin sudo mkdir -p /opt/nri/plugins sudo ln -s /usr/local/bin/v010-adapter /opt/nri/plugins/00-v010-adapter ```