chore(deps): update redis docker tag to v8

[renovate]

This PR contains the following updates:

Package	Update	Change
redis	major	7-alpine → 8-alpine

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Configuration

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[claude]

PR Review: Update Redis Docker tag to v8

Summary

This PR updates the Redis Docker image from 7-alpine to 8-alpine in the development Docker Compose configuration. Overall, this is a low-risk dependency update that should be safe to merge.

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✅ Code Quality & Best Practices

Positive:

• Clean, minimal change targeting only the necessary file
• Follows semantic versioning for infrastructure dependencies
• Automated by Renovate, ensuring consistency

Note:

• The main production config (docker-compose.yml) already uses redis:8-alpine (line 36), so this PR brings the dev environment into alignment with production. This is actually a good consistency improvement.

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🔍 Compatibility Analysis

Redis 8 Compatibility:
✅ The Python redis library version 5.3.1 (used by arq 0.26.3) supports Redis 8
✅ The arq task queue library 0.26.3 (released Jan 2025) is compatible with Redis 8
✅ No breaking changes in Redis 8 affect the basic features used:

• Append-only file (AOF) persistence
• Basic key-value operations
• Distributed locks (redis.lock())
• Job queue operations

Usage Pattern Review:
The codebase uses Redis for:

1. Task Queue (via arq): enqueue_job(), job management
2. Distributed Locks: redis.lock() for preference update race condition prevention
3. Basic Caching: set() operations with deduplication keys
4. Health Checks: redis-cli ping (unchanged between v7 and v8)

All these patterns are fully supported in Redis 8.

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🔒 Security Considerations

✅ No security concerns identified:

• Redis 8 includes security improvements over Redis 7
• Alpine Linux base image continues to receive security updates
• No sensitive data exposure risk from this change
• The --appendonly yes persistence flag remains compatible

Recommendation: Consider adding REDIS_PASSWORD for development environments (currently only documented for production in DEPLOY.md) to match production security practices.

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⚡ Performance Considerations

Potential Benefits:

• Redis 8 includes performance improvements for persistence and replication
• No performance regressions expected for the current usage patterns
• Alpine image maintains small footprint

Note: No performance-critical code paths identified that would be affected by this update.

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🧪 Test Coverage

Current State:

• No integration tests verify Redis version compatibility
• CI uses Redis via service containers (.github/workflows/ci-backend.yml:79)

Recommendations:

1. ✅ Safe to merge - The CI pipeline will verify compatibility automatically
2. Consider adding a smoke test to verify arq worker can connect to Redis successfully
3. Test the development environment locally with make up && make dev-all before merging

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📋 Additional Observations

Consistency Check:

• ✅ Production config already uses redis:8-alpine
• ✅ This PR brings dev environment in sync
• ⚠️ docker-compose.override.yml also uses redis:7-alpine - consider updating it as well for full consistency

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🎯 Verdict

Recommendation: ✅ APPROVE with minor suggestion

This is a safe, low-risk upgrade that:

• Improves dev/prod environment consistency
• Maintains backward compatibility with existing code
• Brings in Redis 8 improvements

Before merging:

1. ✅ Verify CI passes (backend tests with Redis)
2. ✅ Test locally: docker compose -f docker-compose.dev.yml up -d
3. 📝 Optional: Update docker-compose.override.yml for complete consistency

Post-merge:
Monitor the arq worker logs for any unexpected Redis connection issues during the first few feed fetch cycles.

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Great work keeping dependencies up to date! 🚀