etcd(ticdc): update etcd cluster member correctly (#12646)

[ti-chi-bot]

This is an automated cherry-pick of #12646

What problem does this PR solve?

Issue Number: close #12368

What is changed and how it works?

When updating etcd client URLs, remove the client that is not a member of the etcd cluster.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)

tiup playground $VERSION --db 1 --kv 1 --pd 3 --ticdc 1 --tiflash 0 --without-monitor
tiup cdc:$VERSION cli changefeed create --sink-uri 'blackhole://'
tiup playground scale-out --pd 1
tiup playground display
tiup playground scale-in --pid 153389 # pick any one from the display

Print only once

[2026/05/21 10:03:39.588 +00:00] [INFO] [client.go:447] ["update endpoints"] [numChange=3->4] [lastEndpoints="[http://127.0.0.1:2382,http://127.0.0.1:2379,http://127.0.0.1:2384]"] [endpoints="[http://127.0.0.1:44765,http://127.0.0.1:2382,http://127.0.0.1:2384,http://127.0.0.1:2379]"]

Questions

Will it cause performance regression or break compatibility?

Do you need to update user documentation, design documentation or monitoring documentation?

Release note

Fixed the bug of using an incorrect etcd client when scaling PD nodes

[gemini-code-assist]

Code Review

This pull request updates the etcd client configuration by removing the AutoSyncInterval, making the isHealthy function private, and refining the healthyChecker.update logic to properly close and remove stale client connections. Feedback was provided regarding the update function, specifically pointing out that an empty endpoint list could lead to unnecessary connection churn and suggesting a guard clause to prevent clearing all clients during transient failures.

[gemini-code-assist]

If syncUrls fails to retrieve the etcd member list (e.g., due to a transient network error or leader election), it returns an empty slice. In the current implementation, this causes the update function to clear all existing clients from the healthyChecker and close their connections. When syncUrls succeeds in a subsequent iteration, all clients will be recreated, leading to unnecessary connection churn and a temporary loss of health monitoring for existing members. Adding a guard to skip the update when eps is empty ensures continuity during transient etcd control plane issues.

	if len(eps) == 0 {
		return
	}
	updateEps := make(map[string]struct{}, len(eps))

[codecov]

Codecov Report

❌ Patch coverage is 0% with 18 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (release-8.5@1d4e139). Learn more about missing BASE report.

Additional details and impacted files

Components	Coverage Δ
cdc	57.6522% <0.0000%> (?)
dm	49.0171% <0.0000%> (?)
engine	50.7219% <0.0000%> (?)

Flag	Coverage Δ
cdc	57.6522% <0.0000%> (?)
unit	53.4621% <0.0000%> (?)

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[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: wk989898

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[wk989898]

/retest

[wk989898]

/retest