Currently, `TransportGetShutdownStatusAction` is executed in a transport thread, this action can do a substantial amount of work (O(# shards) in some cases) in the transport thread preventing pending transport tasks to make progress and potentially causing cluster instability. This action should be dispatched into a different thread pool to avoid such issues.
x-pack/plugin/shutdown/src/main/java/org/elasticsearch/xpack/shutdown/RestGetShutdownStatusAction.java
public class RestGetShutdownStatusAction extends BaseRestHandler {
    @Override
    public String getName() {
        return "get_shutdown_status";
    }
    @Override
    public List<Route> routes() {
        return List.of(
            new Route(RestRequest.Method.GET, "/_nodes/{nodeId}/shutdown"),
            new Route(RestRequest.Method.GET, "/_nodes/shutdown")
        );
    }
    @Override
    protected RestChannelConsumer prepareRequest(RestRequest request, NodeClient client) {
        String[] nodeIds = Strings.commaDelimitedListToStringArray(request.param("nodeId"));
        return channel -> client.execute(
            GetShutdownStatusAction.INSTANCE,
            new GetShutdownStatusAction.Request(nodeIds),
            new RestToXContentListener<>(channel)
        );
    }
}