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Using Device Manager

What Device Manager Does

Device Manager is a Kubelet feature that provides a mechanism for advertising specialized node hardware resources with the help of Kubelet plug-ins known as device plug-ins.

Any vendor can implement a device plug-in to advertise their specialized hardware without requiring any upstream code changes.

OKD supports the device plug-in API, but the device plug-in containers are supported by individual vendors.

Device Manager advertises devices as Extended Resources. User pods can consume devices, advertised by Device Manager, using the same Limit/Request mechanism, which is used for requesting any other Extended Resource.

Registration

Upon start, the device plug-in registers itself with Device Manager invoking Register on the /var/lib/kubelet/device-plugins/kubelet.sock and starts a gRPC service at /var/lib/kubelet/device-plugins/<plugin>.sock for serving Device Manager requests.

Device Discovery and Health Monitoring

Device Manager, while processing a new registration request, invokes ListAndWatch remote procedure call (RPC) at the device plug-in service. In response, Device Manger gets a list of Device objects from the plug-in over a gRPC stream. Device Manager will keep watching on the stream for new updates from the plug-in. On the plug-in side, the plug-in will also keep the stream open and whenever there is a change in the state of any of the devices, a new device list is sent to the Device Manager over the same streaming connection.

Device Allocation

While handling a new pod admission request, Kubelet passes requested Extended Resources to the Device Manager for device allocation. Device Manager checks in its database to verify if a corresponding plug-in exists or not. If the plug-in exists and there are free allocatable devices as well as per local cache, Allocate RPC is invoked at that particular device plug-in.

Additionally, device plug-ins can also perform several other device-specific operations, such as driver installation, device initialization, and device resets. These functionalities vary from implementation to implementation.

Enabling Device Manager

Enable Device Manager to implement a device plug-in to advertise specialized hardware without any upstream code changes.

  1. Enable Device Manager support on the target node or nodes:

    $ oc describe configmaps <name>

    For example:

    $ oc describe configmaps node-config-infra
...
kubeletArguments:
...
  feature-gates:
  - DevicePlugins=true

  2. Ensure that Device Manager was actually enabled by confirming that /var/lib/kubelet/device-plugins/kubelet.sock is created on the node. This is the UNIX domain socket on which the Device Manager gRPC server listens for new plug-in registrations. This sock file is created when the Kubelet is started only if Device Manager is enabled.