[grid] Add Distributor Redis-backed implementation as built-in support by VietND96 · Pull Request #17396 · SeleniumHQ/selenium

VietND96 · 2026-04-26T10:25:47Z

🔗 Related Issues

💥 What does this PR do?

Redis-backed Distributor implementation for Selenium Grid, enabling stateless horizontal scaling with multiple Distributor replicas sharing state through Redis

Three new classes implement the full Distributor / GridModel / NodeRegistry contract against Redis:

RedisBackedGridModel: all grid state (node blobs, availability sets, slot session keys, health fail counts, last-touch timestamps) lives in Redis
RedisBackedNodeRegistry — per-node health check runs are leader-elected via a per-node Redis SET NX PX lock, so exactly one replica performs the HTTP /status probe per interval regardless of replica count. On startup, reconstructs RemoteNode proxies from Redis availability sets, so new replicas immediately know about all live nodes.
RedisBackedDistributor — extends Distributor, publishes a per-instance heartbeat key every 10 s with a 30 s TTL, and writes a draining marker on close() for graceful shutdown. isReady() checks both the Redis connection and the event bus. Includes a static create(Config) factory that reads distributor.backend-url from config for use with --distributor-implementation.

🔧 Implementation Notes

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💡 Additional Considerations

🔄 Types of changes

Cleanup (formatting, renaming)
Bug fix (backwards compatible)
New feature (non-breaking change which adds functionality and tests!)
Breaking change (fix or feature that would cause existing functionality to change)

Signed-off-by: Viet Nguyen Duc <nguyenducviet4496@gmail.com>

qodo-code-review · 2026-04-26T10:26:06Z

Review Summary by Qodo

Add Redis-backed Distributor implementation for stateless Grid scaling

✨ Enhancement

Walkthroughs

Description

• Adds Redis-backed Distributor implementation for stateless horizontal scaling
• Implements RedisBackedGridModel, RedisBackedNodeRegistry, and RedisBackedDistributor classes
• Enables multiple Distributor replicas to share state via Redis with atomic slot reservation
• Includes distributed health-check coordination via Redis leader-election locks
• Adds comprehensive test coverage for Redis-backed components
• Updates configuration to support --distributor-backend-url parameter

File Changes

1. java/src/org/openqa/selenium/grid/distributor/redis/RedisBackedDistributor.java ✨ Enhancement +727/-0

Main Redis-backed Distributor with session management

java/src/org/openqa/selenium/grid/distributor/redis/RedisBackedDistributor.java

2. java/src/org/openqa/selenium/grid/distributor/redis/RedisBackedGridModel.java ✨ Enhancement +673/-0

Redis-backed grid state storage and slot management

java/src/org/openqa/selenium/grid/distributor/redis/RedisBackedGridModel.java

3. java/src/org/openqa/selenium/grid/distributor/redis/RedisBackedNodeRegistry.java ✨ Enhancement +636/-0

Redis-backed node registry with health check coordination

java/src/org/openqa/selenium/grid/distributor/redis/RedisBackedNodeRegistry.java

View more (15)

4. java/src/org/openqa/selenium/grid/distributor/config/DistributorFlags.java ⚙️ Configuration changes +12/-0

Add distributor-backend-url configuration parameter

java/src/org/openqa/selenium/grid/distributor/config/DistributorFlags.java

5. java/src/org/openqa/selenium/grid/distributor/config/DistributorOptions.java ✨ Enhancement +13/-0

Add getBackendUri method for backend configuration

java/src/org/openqa/selenium/grid/distributor/config/DistributorOptions.java

6. java/src/org/openqa/selenium/redis/GridRedisClient.java ✨ Enhancement +52/-0

Add Redis operations for slot reservation and key scanning

java/src/org/openqa/selenium/redis/GridRedisClient.java

7. java/src/org/openqa/selenium/grid/distributor/httpd/DistributorServer.java ✨ Enhancement +7/-1

Update readiness check response to JSON format

java/src/org/openqa/selenium/grid/distributor/httpd/DistributorServer.java

8. java/src/org/openqa/selenium/grid/commands/InfoCommand.java 📝 Documentation +5/-0

Add distributor help topic to info command

java/src/org/openqa/selenium/grid/commands/InfoCommand.java

9. java/src/org/openqa/selenium/grid/commands/distributor.txt 📝 Documentation +105/-0

Documentation for Distributor backends and configuration

java/src/org/openqa/selenium/grid/commands/distributor.txt

10. java/src/org/openqa/selenium/grid/commands/info.txt 📝 Documentation +1/-0

Update info command to reference distributor topic

java/src/org/openqa/selenium/grid/commands/info.txt

11. java/test/org/openqa/selenium/grid/distributor/redis/RedisBackedDistributorTest.java 🧪 Tests +246/-0

Test suite for Redis-backed Distributor functionality

java/test/org/openqa/selenium/grid/distributor/redis/RedisBackedDistributorTest.java

12. java/test/org/openqa/selenium/grid/distributor/redis/RedisBackedGridModelTest.java 🧪 Tests +416/-0

Test suite for Redis-backed grid model operations

java/test/org/openqa/selenium/grid/distributor/redis/RedisBackedGridModelTest.java

13. java/test/org/openqa/selenium/grid/distributor/redis/RedisBackedNodeRegistryTest.java 🧪 Tests +169/-0

Test suite for Redis-backed node registry

java/test/org/openqa/selenium/grid/distributor/redis/RedisBackedNodeRegistryTest.java

14. java/src/org/openqa/selenium/grid/distributor/redis/BUILD.bazel Build +36/-0

Build configuration for Redis distributor module

java/src/org/openqa/selenium/grid/distributor/redis/BUILD.bazel

15. java/test/org/openqa/selenium/grid/distributor/redis/BUILD.bazel Build +42/-0

Build configuration for Redis distributor tests

java/test/org/openqa/selenium/grid/distributor/redis/BUILD.bazel

16. java/src/org/openqa/selenium/grid/distributor/httpd/BUILD.bazel Build +2/-0

Add Redis distributor dependency to build

java/src/org/openqa/selenium/grid/distributor/httpd/BUILD.bazel

17. java/src/org/openqa/selenium/grid/BUILD.bazel Build +1/-0

Add Redis distributor to Grid runtime dependencies

java/src/org/openqa/selenium/grid/BUILD.bazel

18. java/src/org/openqa/selenium/events/zeromq/BUILD.bazel Build +1/-0

Update visibility for Redis distributor tests

java/src/org/openqa/selenium/events/zeromq/BUILD.bazel

qodo-code-review · 2026-04-26T10:26:07Z

Code Review by Qodo

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Signed-off-by: Viet Nguyen Duc <nguyenducviet4496@gmail.com>

VietND96 · 2026-04-26T19:03:42Z

/review

qodo-code-review · 2026-04-26T19:04:08Z

PR Reviewer Guide 🔍

Here are some key observations to aid the review process:

🎫 Ticket compliance analysis 🔶 1234 - Partially compliant Compliant requirements: Non-compliant requirements: Fix regression where Selenium 2.48 does not trigger JavaScript in a link `href` when invoking `click()` Ensure behavior is correct specifically with Firefox 42 on affected platforms Provide/maintain a reproducible test case demonstrating the fix Requires further human verification: 5678 - Partially compliant Compliant requirements: Non-compliant requirements: Investigate and fix `ChromeDriver` multi-instantiation errors showing `ConnectFailure (Connection refused)` Ensure subsequent `ChromeDriver` instantiations do not log connection-refused errors Provide guidance or a code change that prevents/reduces the observed connection failures Requires further human verification:
⏱️ Estimated effort to review: 4 🔵🔵🔵🔵⚪
🧪 PR contains tests
🔒 No security concerns identified
⚡ Recommended focus areas for review Thread Leak A dedicated scheduled executor is created for the Redis distributor heartbeat but is not stored or shut down in `close()`. This can leak threads and keep Redis writes running after shutdown; consider holding a reference and shutting it down alongside the other services. // Publish this replica's liveness heartbeat to Redis. Executors.newSingleThreadScheduledExecutor( r -> { Thread t = new Thread(r); t.setName("Redis Distributor - Heartbeat"); t.setDaemon(true); return t; }) .scheduleAtFixedRate( GuardedRunnable.guard(this::publishHeartbeat), 0, 10, TimeUnit.SECONDS); new JMXHelper().register(this); } Content-Type The readiness endpoint sets `Content-Type` to plain text while returning JSON content. This mismatch may break clients expecting correct content negotiation; consider switching to a JSON media type (or returning plain text consistently). return new HttpResponse() .setStatus(ready ? HTTP_OK : HTTP_UNAVAILABLE) .setHeader("Content-Type", MediaType.PLAIN_TEXT_UTF_8.toString()) .setContent( Contents.asJson( Map.of( "ready", ready, "message", ready ? "Distributor is ready" : "Distributor is not ready"))); }; Redis Scan Cost The new `scanKeys` helper iterates the entire keyspace (even if incrementally) and is used for node cleanup. In large deployments this can still be expensive; consider constraining key patterns further, adding backoff/limits, or using Redis data structures to avoid scans for operational paths. /** Scans keys matching the pattern using SCAN cursor iteration (non-blocking). */ public List<String> scanKeys(String pattern) { List<String> result = new ArrayList<>(); ScanCursor cursor = ScanCursor.INITIAL; ScanArgs args = ScanArgs.Builder.matches(pattern).limit(100); do { KeyScanCursor<String> scanResult = connection.sync().scan(cursor, args); result.addAll(scanResult.getKeys()); cursor = scanResult; } while (!cursor.isFinished()); return result; }

Signed-off-by: Viet Nguyen Duc <nguyenducviet4496@gmail.com>

[grid] Add Distributor Redis-backed as default implementation

2c59d2d

Signed-off-by: Viet Nguyen Duc <nguyenducviet4496@gmail.com>

selenium-ci added B-grid Everything grid and server related C-java Java Bindings B-build Includes scripting, bazel and CI integrations labels Apr 26, 2026

VietND96 changed the title ~~[grid] Add Distributor Redis-backed as default implementation~~ [grid] Add Distributor Redis-backed implementation as built-in support Apr 26, 2026

Use test container to start Redis server

461b29b

Signed-off-by: Viet Nguyen Duc <nguyenducviet4496@gmail.com>

VietND96 force-pushed the distributor-redis-backed branch from 5d79014 to 461b29b Compare April 26, 2026 17:54

qodo-code-review Bot added the Review effort 4/5 label Apr 26, 2026

Fix review comments

1ad3a9c

Signed-off-by: Viet Nguyen Duc <nguyenducviet4496@gmail.com>

VietND96 merged commit 8cc26f7 into trunk Apr 27, 2026
89 of 91 checks passed

VietND96 deleted the distributor-redis-backed branch April 27, 2026 04:45

VietND96 mentioned this pull request May 12, 2026

[grid] Bundle Redis-backed SessionMap by default #17441

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[grid] Add Distributor Redis-backed implementation as built-in support#17396

[grid] Add Distributor Redis-backed implementation as built-in support#17396
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VietND96 commented Apr 26, 2026

🔗 Related Issues

💥 What does this PR do?

🔧 Implementation Notes

🤖 AI assistance

💡 Additional Considerations

🔄 Types of changes

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qodo-code-review Bot commented Apr 26, 2026

Review Summary by Qodo

Walkthroughs

File Changes

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qodo-code-review Bot commented Apr 26, 2026

Code Review by Qodo

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VietND96 commented Apr 26, 2026

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