[BUG] NodeVersionAllocationDecider should get Replication Type from index meta instead of node settings

[KunjueYu]

Describe the bug

The class org.opensearch.cluster.routing.allocation.decider.NodeVersionAllocationDecider misuses the node settings to get the replication type value. As INDEX_REPLICATION_TYPE_SETTING is an indexScope setting, we should get the value from the index metadata.

public class NodeVersionAllocationDecider extends AllocationDecider {

    public static final String NAME = "node_version";

    private final ReplicationType replicationType;

    public NodeVersionAllocationDecider(Settings settings) {
        replicationType = IndexMetadata.INDEX_REPLICATION_TYPE_SETTING.get(settings);
    }

    @Override
    public Decision canAllocate(ShardRouting shardRouting, RoutingNode node, RoutingAllocation allocation) {
        if (shardRouting.primary()) {
            if (replicationType == ReplicationType.SEGMENT) {

Related component

Cluster Manager

To Reproduce

1. build a cluster with different node versions.
2. create a index with segment replication enabled.
3. allocate the primary shard to a higher-version node while the corresponding replica shard on a lower-version node.
4. Contrary to expectations, the allocation will succeed.

Expected behavior

I believe the correct code should be like

public class NodeVersionAllocationDecider extends AllocationDecider {

    public static final String NAME = "node_version";

    public NodeVersionAllocationDecider() {
    }

    @Override
    public Decision canAllocate(ShardRouting shardRouting, RoutingNode node, RoutingAllocation allocation) {
        if (shardRouting.primary()) {
            IndexMetadata indexMd = allocation.metadata().getIndexSafe(shardRouting.index());
            final ReplicationType replicationType = IndexMetadata.INDEX_REPLICATION_TYPE_SETTING.get(indexMd.getSettings());
            if (replicationType == ReplicationType.SEGMENT) {
                List<ShardRouting> replicas = allocation.routingNodes()

Additional Details

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[andrross]

[Triage - attendees 1 2 3 4 5 6]
@KunjueYu Thanks for filing! Any interest in putting together a PR to fix this issue along with a test that replicates it?

[KunjueYu]

I have opened a pr. I'd appreciate it if you could review it.

[Triage - attendees 1 2 3 4 5 6] @KunjueYu Thanks for filing! Any interest in putting together a PR to fix this issue along with a test that replicates it?