doc: capture device-plugin stricter workflow ordering explicitly

Based on kubelet device manager refactoring done in 1.25 release,
there is stricter ordering requirements where the device plugin
MUST start a gRPC service before registering itself to kubelet.
In case this ordering is not followed, the plugin registration
will fail.

Signed-off-by: Swati Sehgal <swsehgal@redhat.com>

content/en/docs/concepts/extend-kubernetes/compute-storage-net/device-plugins.md

@@ -87,60 +87,65 @@ spec:
 
 The general workflow of a device plugin includes the following steps:
 
-* Initialization. During this phase, the device plugin performs vendor specific
+1. Initialization. During this phase, the device plugin performs vendor-specific
   initialization and setup to make sure the devices are in a ready state.
 
-* The plugin starts a gRPC service, with a Unix socket under host path
+1. The plugin starts a gRPC service, with a Unix socket under the host path
   `/var/lib/kubelet/device-plugins/`, that implements the following interfaces:
 
-  ```gRPC
-  service DevicePlugin {
-        // GetDevicePluginOptions returns options to be communicated with Device Manager.
-        rpc GetDevicePluginOptions(Empty) returns (DevicePluginOptions) {}
+    ```gRPC
+    service DevicePlugin {
+          // GetDevicePluginOptions returns options to be communicated with Device Manager.
+          rpc GetDevicePluginOptions(Empty) returns (DevicePluginOptions) {}
 
-        // ListAndWatch returns a stream of List of Devices
-        // Whenever a Device state change or a Device disappears, ListAndWatch
-        // returns the new list
-        rpc ListAndWatch(Empty) returns (stream ListAndWatchResponse) {}
+          // ListAndWatch returns a stream of List of Devices
+          // Whenever a Device state change or a Device disappears, ListAndWatch
+          // returns the new list
+          rpc ListAndWatch(Empty) returns (stream ListAndWatchResponse) {}
 
-        // Allocate is called during container creation so that the Device
-        // Plugin can run device specific operations and instruct Kubelet
-        // of the steps to make the Device available in the container
-        rpc Allocate(AllocateRequest) returns (AllocateResponse) {}
+          // Allocate is called during container creation so that the Device
+          // Plugin can run device specific operations and instruct Kubelet
+          // of the steps to make the Device available in the container
+          rpc Allocate(AllocateRequest) returns (AllocateResponse) {}
 
-        // GetPreferredAllocation returns a preferred set of devices to allocate
-        // from a list of available ones. The resulting preferred allocation is not
-        // guaranteed to be the allocation ultimately performed by the
-        // devicemanager. It is only designed to help the devicemanager make a more
-        // informed allocation decision when possible.
-        rpc GetPreferredAllocation(PreferredAllocationRequest) returns (PreferredAllocationResponse) {}
+          // GetPreferredAllocation returns a preferred set of devices to allocate
+          // from a list of available ones. The resulting preferred allocation is not
+          // guaranteed to be the allocation ultimately performed by the
+          // devicemanager. It is only designed to help the devicemanager make a more
+          // informed allocation decision when possible.
+          rpc GetPreferredAllocation(PreferredAllocationRequest) returns (PreferredAllocationResponse) {}
 
-        // PreStartContainer is called, if indicated by Device Plugin during registeration phase,
-        // before each container start. Device plugin can run device specific operations
-        // such as resetting the device before making devices available to the container.
-        rpc PreStartContainer(PreStartContainerRequest) returns (PreStartContainerResponse) {}
-  }
-  ```
+          // PreStartContainer is called, if indicated by Device Plugin during registeration phase,
+          // before each container start. Device plugin can run device specific operations
+          // such as resetting the device before making devices available to the container.
+          rpc PreStartContainer(PreStartContainerRequest) returns (PreStartContainerResponse) {}
+    }
+    ```
 
-  {{< note >}}
-  Plugins are not required to provide useful implementations for
-  `GetPreferredAllocation()` or `PreStartContainer()`. Flags indicating which
-  (if any) of these calls are available should be set in the `DevicePluginOptions`
-  message sent back by a call to `GetDevicePluginOptions()`. The `kubelet` will
-  always call `GetDevicePluginOptions()` to see which optional functions are
-  available, before calling any of them directly.
-  {{< /note >}}
+    {{< note >}}
+    Plugins are not required to provide useful implementations for
+    `GetPreferredAllocation()` or `PreStartContainer()`. Flags indicating
+    the availability of these calls, if any, should be set in the `DevicePluginOptions`
+    message sent back by a call to `GetDevicePluginOptions()`. The `kubelet` will
+    always call `GetDevicePluginOptions()` to see which optional functions are
+    available, before calling any of them directly.
+    {{< /note >}}
 
-* The plugin registers itself with the kubelet through the Unix socket at host
+1. The plugin registers itself with the kubelet through the Unix socket at host
   path `/var/lib/kubelet/device-plugins/kubelet.sock`.
 
-* After successfully registering itself, the device plugin runs in serving mode, during which it keeps
-  monitoring device health and reports back to the kubelet upon any device state changes.
-  It is also responsible for serving `Allocate` gRPC requests. During `Allocate`, the device plugin may
-  do device-specific preparation; for example, GPU cleanup or QRNG initialization.
-  If the operations succeed, the device plugin returns an `AllocateResponse` that contains container
-  runtime configurations for accessing the allocated devices. The kubelet passes this information
-  to the container runtime.
+    {{< note >}}
+    The ordering of the workflow is important. A plugin MUST start serving gRPC
+    service before registering itself with kubelet for successful registration.
+    {{< /note >}}
+
+1. After successfully registering itself, the device plugin runs in serving mode, during which it keeps
+   monitoring device health and reports back to the kubelet upon any device state changes.
+   It is also responsible for serving `Allocate` gRPC requests. During `Allocate`, the device plugin may
+   do device-specific preparation; for example, GPU cleanup or QRNG initialization.
+   If the operations succeed, the device plugin returns an `AllocateResponse` that contains container
+   runtime configurations for accessing the allocated devices. The kubelet passes this information
+   to the container runtime.
 
 ### Handling kubelet restarts