[CI] Maven Central dependency-resolution failures (Connection reset / 502) break required build jobs and block unrelated PRs #7767

Summary

Several required CI checks fail non-deterministically because Maven cannot resolve/download dependencies from Maven Central — independent of the PR under test. This marks otherwise-approved PRs as BLOCKED and prevents merge.

Affected jobs

build (shenyu-integrated-test-*), build-docker-images, sql-matrix, list-contract, and pr_build (on some PRs).

Evidence (job logs)

build (shenyu-integrated-test-combination) — #6457, job 116507895457

[ERROR] Failed to execute goal on project shenyu-examples-eureka: Could not collect dependencies for project org.apache.shenyu:shenyu-examples-eureka:jar:2.7.2-SNAPSHOT
[ERROR] Failed to read artifact descriptor for org.glassfish.jersey.core:jersey-client:jar:3.0.5
[ERROR] Caused by: The following artifacts could not be resolved: org.glassfish.jersey.core:jersey-client:pom:3.0.5 (absent):
        Could not transfer artifact ... from/to central (https://repo.maven.apache.org/maven2): Connection reset
[INFO] BUILD FAILURE

pr_build — #7184, job 110137674074

[ERROR] Failed to execute goal on project shenyu-spring-boot-starter-client-beat: Could not resolve dependencies for project org.apache.shenyu:shenyu-spring-boot-starter-client-beat:jar:2.7.2-SNAPSHOT

Other runs additionally show HTTP 502 on groovy-bom:3.0.10, swagger-annotations-jakarta:2.2.22, slf4j-api:1.5.6, and maven cache is not found (cache not restored).

Cascade into e2e

When build-docker-images fails, the shenyu-images artifact is never produced, so dependent e2e jobs fail with:

##[error]Unable to download artifact(s): Artifact not found for name: shenyu-images

(e.g. #7091). A single Maven flake therefore becomes a broad e2e failure.

Impact

Approved PRs currently BLOCKED by these flaky required checks (sample): #6457, #7105, #7113, #7183, #7184, #7193, #7406, #7414, #7618, #7639, #7661, #7668, #7691.

Proposed mitigations

• Add Maven download retries: -Dmaven.wagon.http.retryHandler.count=3 -Dmaven.wagon.http.retryHandler.requestSentEnabled=true (and consider -Dmaven.resolver.transport=wagon).
• Make the ~/.m2 cache restore reliable and cache ~/.m2/repository (cf. closed [BUG] [CI] Maven cache key collision causes flaky e2e-case failures #6382).
• Auto-retry build (shenyu-integrated-test-*) / build-docker-images on dependency-resolution errors.
• Reconsider marking infra-only jobs as required for merge (or allow a maintainer re-run to satisfy them).

Relates to #6281 (flaky-test tracking).