Add toXContent and fromXContent for DiscoveryNode and DiscoveryNodes

[shiv0408]

Description

We need to upload the DiscoveryNodes object to remote to enable the cluster state publication flow from remote. To do that we need to parse DiscoveryNodes object to and from XContent.

Related Issues

Resolves #13691
Meta issue #13683

Check List

• New functionality includes testing.
  • All tests pass
• New functionality has been documented.
  • New functionality has javadoc added
• Failing checks are inspected and point to the corresponding known issue(s) (See: Troubleshooting Failing Builds)
• Commits are signed per the DCO using --signoff
• Commit changes are listed out in CHANGELOG.md file (See: Changelog)
• Public documentation issue/PR created

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[github-actions]

❌ Gradle check result for 5870c05: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[github-actions]

❌ Gradle check result for 7d1a599: FAILURE

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[github-actions]

❕ Gradle check result for 93d13e2: UNSTABLE

• TEST FAILURES:

      1 org.opensearch.smoketest.SmokeTestMultiNodeClientYamlTestSuiteIT.test {yaml=search.aggregation/230_composite/composite aggregation date_histogram profile shows filter rewrite info}

Please review all flaky tests that succeeded after retry and create an issue if one does not already exist to track the flaky failure.

[shiv0408]

SmokeTestMultiNodeClientYamlTestSuiteIT test has been identified as flaky previously in #9332

[dbwiddis]

A few comments.

Also I've seen the method you call fromXContent called parse(). Since it's a static method and not enforced by the interface, in theory you can make it whatever you want... I see a lot of both throughout the codebase so either is probably fine, but I'd suggest making this consistent with other code around where it will be used... if that's fromXContent() that's fine, I haven't dug into the context.

[lukas-vlcek]

@shiv0408 Would you mind modifying issue description and adding a ticket number that requires this change please? I would be interested in learning more about why exactly this is needed (I assume this is relevant to remote storage?).

[github-actions]

❌ Gradle check result for f151e00: FAILURE

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[shiv0408]

@lukas-vlcek apologies for late response, I have modified the description of the PR to include the issue for this. And yes, this effort is required for remote state publication.

[shiv0408]

@dbwiddis Thanks for reviewing the changes. I have pushed a commit to address your concerns. Can you please take another look at the changes?

Also I've seen the method you call fromXContent called parse()

We are consistently using fromXContent method name for de-serializing the object for all the objects with are getting used in our remote cluster state flow.

[github-actions]

❌ Gradle check result for 6a54fb1: FAILURE

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[github-actions]

❌ Gradle check result for 08a10cb: FAILURE

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[github-actions]

❌ Gradle check result for a33fe7b: FAILURE

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[github-actions]

✅ Gradle check result for 2d2127e: SUCCESS

[shwetathareja]

You don't control the toString() you are using TransportAddress.toString() which calls NetworkAddress.format(address); . If toString() implementation changes, your fromString() will break.

[shwetathareja]

As discussed, it may not be scalable to keep on adding fromXContent to ephemeral objects which only have StreamInput/ StreamOutput implementation for node to node cluster state publication. Lets use that only serde. Also for other objects like ClusterState.Custom or Metadata.Custom where plugins can provides custom implementations, they may not have fromXContent method implemented and then it will break the remote state which is not desired.

[shiv0408]

Closing this as we are not gonna be using XContent for storing cluster state ephemeral objects brings overhead in maintenance of writeTo, readFrom and toXContent with additional fromXContent. We have added RemoteWriteableEntity with ser/de that can be done with InputStream as well.
So, discarding this PR and other ephemeral objects.