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https://github.com/k8snetworkplumbingwg/multus-cni.git
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9f3e6b0da0
This change introduces prometheus metric exporter support for multus-daemon, thick plugin.
94 lines
4.6 KiB
Markdown
94 lines
4.6 KiB
Markdown
# Multus Thick plugin
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Multus CNI can also be deployed using a thick plugin architecture, which is
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characterized by a client/server architecture.
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The client - which will be referred to as "shim" - is a binary executable
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located on the Kubernetes node's file-system that
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[speaks CNI](https://github.com/containernetworking/cni/blob/master/SPEC.md#section-2-execution-protocol):
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the runtime - Kubernetes - passes parameters to the plugin via environment
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variables and configuration - which is passed via stdin.
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The plugin returns a result on stdout on success, or an error on stderr if the
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operation fails. Configuration and results are a JSON encoded string.
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Once the shim is invoked by the runtime (Kubernetes) it will contact the
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multus-daemon (server) via a unix domain socket which is bind mounted to the
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host's file-system; the multus-daemon is the one that will do all the
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heavy-pulling: fetch the delegate CNI configuration from the corresponding
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`net-attach-def`, compute the `RuntimeConfig`, and finally, invoke the delegate.
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It will then return the result of the operation back to the client.
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Please refer to the diagram below for a visual representation of the flow
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described above:
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```
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┌─────────┐ ┌───────┐ ┌────────┐ ┌──────────┐
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│ │ cni ADD/DEL │ │ REST POST │ │ cni ADD/DEL │ │
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│ runtime ├────────────►│ shim │===========│ daemon ├────────────►│ delegate │
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│ │<------------│ │ │ │<------------│ │
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└─────────┘ └───────┘ └────────┘ └──────────┘
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```
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## How to use it
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### Configure Deployment
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If your delegate CNI plugin requires some files which is in container host, please update
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update `deployments/multus-daemonset-thick.yml` to add directory into multus-daemon pod.
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For example, flannel requires `/run/flannel/subnet.env`, so you need to mount this directory
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into the multus-daemon pod.
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Required directory/files are different for each CNI plugin, so please refer your CNI plugin.
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### Deployment
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There is a dedicated multus daemonset specification for users wanting to use
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this thick plugin variant. This reference deployment spec of multus can be
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deployed by following these commands:
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```bash
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kubectl apply -f deployments/multus-daemonset-thick.yml
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```
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### Command line parameters
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Multus thick plugin variant accepts the same
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[entrypoint arguments](https://github.com/k8snetworkplumbingwg/multus-cni/blob/master/docs/how-to-use.md#entrypoint-script-parameters)
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its thin counterpart allows - with the following exceptions:
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- `additional-bin-dir`
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- `binDir`
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- `cleanup-config-on-exit`
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- `cniDir`
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- `multus-kubeconfig-file-host`
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- `rename-conf-file`
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- `restart-crio`
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- `skip-multus-binary-copy`
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It is important to refer that these are command line parameters to the golang
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binary; as such, they should be passed using a single dash ("-") e.g.
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`-additional-bin-dir=/opt/multus/bin`, `-multus-log-level=debug`, etc.
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Furthermore, it also accepts a new command line parameter, where the user
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specifies the path to the server configuration:
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- `config`: Defaults to `"/etc/cni/net.d/multus.d/daemon-config.json"`
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- `metricsPort`: Metrics port (of multus' metric exporter), default is disable
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### Server configuration
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The server configuration is encoded in JSON, and allows the following keys:
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- `"chrootDir"`: Specify the directory which points to host root from the pod. See 'Chroot configuration' section for the details.
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- `"socketDir"`: Specify the location where the unix domain socket used for
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client/server communication will be located. Defaults to `"/run/multus-cni"`.
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In addition, you can add any configuration which is in [configuration reference](https://github.com/k8snetworkplumbingwg/multus-cni/blob/master/docs/configuration.md#multus-cni-configuration-reference). Server configuration override multus CNI configuration (e.g. `/etc/cni/net.d/00-multus.conf`)
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#### Chroot configuration
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In thick plugin case, delegate CNI plugin is executed by multus-daemon from Pod, hence if the delegate CNI requires resources in container host, for example unix socket or even file, then CNI plugin is failed to execute because multus-daemon runs in Pod. Multus-daemon supports "chrootDir" option which executes delegate CNI under chroot (to container host).
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This configuration is enabled in deployments/multus-daemonset-thick.yml as default.
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