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/test/java/org/elasticsearch/xpack/shutdown/TransportGetShutdownStatusActionTests.java
import org.elasticsearch.cluster.routing.RoutingTable;
import org.elasticsearch.cluster.routing.ShardRouting;
import org.elasticsearch.cluster.routing.ShardRoutingState;
import org.elasticsearch.cluster.routing.TestShardRouting;
import org.elasticsearch.cluster.routing.UnassignedInfo;
import org.elasticsearch.cluster.routing.allocation.AllocationService;
import org.elasticsearch.cluster.routing.allocation.RoutingAllocation;
import org.elasticsearch.cluster.routing.allocation.allocator.BalancedShardsAllocator;
import org.elasticsearch.cluster.routing.allocation.decider.AllocationDecider;
import org.elasticsearch.cluster.routing.allocation.decider.AllocationDeciders;
import org.elasticsearch.cluster.routing.allocation.decider.Decision;
import org.elasticsearch.cluster.routing.allocation.decider.NodeReplacementAllocationDecider;
import org.elasticsearch.cluster.routing.allocation.decider.NodeShutdownAllocationDecider;
import org.elasticsearch.common.settings.Settings;
import org.elasticsearch.common.transport.TransportAddress;
import org.elasticsearch.gateway.GatewayAllocator;
import org.elasticsearch.index.Index;
import org.elasticsearch.index.IndexVersion;
import org.elasticsearch.index.shard.ShardId;
import org.elasticsearch.node.Node;
import org.elasticsearch.snapshots.SnapshotShardSizeInfo;
import org.elasticsearch.snapshots.SnapshotsInfoService;
import org.elasticsearch.test.ESTestCase;
import org.elasticsearch.test.gateway.TestGatewayAllocator;
import org.elasticsearch.xpack.core.ilm.ErrorStep;
import org.elasticsearch.xpack.core.ilm.LifecycleOperationMetadata;
import org.elasticsearch.xpack.core.ilm.OperationMode;
import org.elasticsearch.xpack.core.ilm.ShrinkAction;
import org.elasticsearch.xpack.core.ilm.ShrinkStep;
import org.elasticsearch.xpack.core.ilm.TimeseriesLifecycleType;