CASSSIDECAR-495: Report each instance's own Sidecar instance id in th…

[bianca-stanciu29]

Problem

Analytics needs the Sidecar instance ID associated with a target Cassandra node when constructing per-instance requests. A client-side hostname lookup cannot reliably supply this information when addresses differ or instances are accessed through a shared endpoint.

Solution

Add an optional sidecarInstanceId to ring entries and token-range replica metadata. The server resolves it from its local instance configuration using the node's address.

• Populate the field for nodes managed by the responding Sidecar.
• Leave it null for nodes that the responding Sidecar does not manage.
• Preserve existing ring fields, replica-map keys, and read/write ranges.
• Keep the previous public RingEntry and ReplicaMetadata constructors. They leave the ID null, so existing client-common callers keep working.

Clients can pass the reported ID as the instanceId query parameter to a Sidecar configured to manage that node.

Related client work: apache/cassandra-analytics#222 (CASSANALYTICS-177).

Scope and topology limitations

These IDs belong to the responding Sidecar's local configuration; they are not cluster-global routing identifiers.

When a Sidecar manages all relevant instances, it can report IDs for all of them. With one Sidecar per node, a response only reports the locally managed node's ID; other entries remain null.

This change does not select a load-balancer backend or rewrite destination addresses. A subsequent request must reach a Sidecar configured to recognize the supplied ID. Initial discovery through a load balancer may still require explicit contact-point routing configuration.

Testing

• RingEntry and ReplicaMetadata: JSON round-trip, deserializing responses without the new field, and the previous constructors.
• InstanceMetadataFetcher: lookup of managed and unmanaged addresses.
• Handlers: both ring routes and the token-range-replicas route. Managed nodes get their ID, unmanaged nodes get null, and the rest of the response is unchanged.

Run locally on the branch merged with current trunk:

• All checkstyle checks, RAT, and SpotBugs on the changed modules.
• JDK 11: all unit tests in client-common, client and adapters-base.
• JDK 17 (DTEST_JAR=dtest-5.0.7.jar): integration-test compilation, RingHandlerTest and InstanceMetadataFetcherTest.

Tests ran with -x checkEnvironment because the macOS multi-node loopback aliases are missing locally. The full server test suite, the integration tests, and an end-to-end load-balancer test have not been run.

JIRA: https://issues.apache.org/jira/browse/CASSSIDECAR-495