intel-device-plugins-for-kubernetes/DEVEL.md

How to develop simple device plugins

To create a simple device plugin without the hassle of developing your own gRPC server, you can use a package included in this repository called github.com/intel/intel-device-plugins-for-kubernetes/pkg/deviceplugin.

All you have to do is instantiate a deviceplugin.Manager and call its Run() method:

func main() {
    ...

    manager := dpapi.NewManager(namespace, plugin)
    manager.Run()
}

The manager's constructor accepts two parameters:

1. namespace which is a string like "color.example.com". All your devices will be exposed under this name space, e.g. "color.example.com/yellow". Please note that one device plugin can register many such "colors". The manager will instantiate multiple gRPC servers for every registered "color".
2. plugin which is a reference to an object implementing one mandatory interface deviceplugin.Scanner.

deviceplugin.Scanner defines one method Scan() which is called only once for every device plugin by deviceplugin.Manager in a goroutine and operates in an infinite loop. A Scan() implementation scans the host for devices and sends all found devices to a deviceplugin.Notifier instance. The deviceplugin.Notifier is implemented and provided by the deviceplugin package itself. The found devices are organized in an instance of deviceplugin.DeviceTree object. The object is filled in with its AddDevice() method:

func (dp *devicePlugin) Scan(notifier deviceplugin.Notifier) error {
    for {
        devTree := deviceplugin.NewDeviceTree()
        ...
        devTree.AddDevice("yellow", devID, deviceplugin.DeviceInfo{
            State: health,
            Nodes: []pluginapi.DeviceSpec{
                {
                    HostPath:      devPath,
                    ContainerPath: devPath,
                    Permissions:   "rw",
                },
            },
        })
        ...
        notifier.Notify(devTree)
    }
}

Optionally, your device plugin may also implement the deviceplugin.PostAllocator interface. If implemented, its method PostAllocate() modifies pluginapi.AllocateResponse responses just before they are sent to kubelet. To see an example, refer to the FPGA plugin which implements this interface to annotate its responses.

Logging

The framework uses klog as its logging framework. It is encouraged for plugins to also use klog to maintain uniformity in the logs and command line options.

The framework initialises klog, so further calls to klog.InitFlags() by plugins should not be necessary. This does add a number of log configuration options to your plugin, which can be viewed with the -h command line option of your plugin.

The framework tries to adhere to the Kubernetes Logging Conventions. The advise is to use the V() levels for Info() calls, as calling Info() with no set level will make configuration and filtering of logging via the command line more difficult.

The default is to not log Info() calls. This can be changed using the plugin command line -v parameter. The additional annotations prepended to log lines by 'klog' can be disabled with the -skip_headers option.