fix: use SLF4J logger in circuit breaker callbacks (fixes missing state-transition logs)

[DominicBM]

Root cause

CircuitBreaker.onOpen/onHalfOpen/onClose callbacks were logging via context.log (Akka Typed's ActorLogger). Those callbacks fire on a Future dispatcher thread — not the actor's message-processing thread. Akka Typed's ActorLogger is not thread-safe: it's guarded by an internal actor-thread check, and when accessed from outside the actor loop it silently drops the message (or throws an AssertionError that is swallowed by the Future chain).

This is why the ElasticSearchResponseHandler rejection warning was appearing (logged inside receiveMessage, safe) while the three state-transition lines from ElasticSearchClient were never appearing — despite 24k rejections proving the breaker was cycling.

Fix

Replace context.log in the three callbacks with the object-level log (LoggerFactory.getLogger(getClass), already declared at line 37 of ElasticSearchClient). A plain SLF4J Logger is thread-safe and works correctly from any thread.

// Before — context.log is unsafe off the actor thread
).onOpen(() => context.log.warn("ElasticSearch circuit breaker opened"))
 .onClose(() => context.log.info("ElasticSearch circuit breaker closed"))
 .onHalfOpen(() => context.log.info("ElasticSearch circuit breaker half-open, testing ES"))

// After — SLF4J logger is thread-safe from any thread
).onOpen(() => log.warn("ElasticSearch circuit breaker opened"))
 .onClose(() => log.info("ElasticSearch circuit breaker closed"))
 .onHalfOpen(() => log.info("ElasticSearch circuit breaker half-open, testing ES"))

Verification

After deploying, aws logs filter-log-events --log-group-name /ecs/api --filter-pattern '"circuit breaker opened"' should return results when the breaker trips.

🤖 Generated with Claude Code

Summary

This PR fixes missing circuit breaker state-transition logs in the ElasticSearch client by replacing thread-unsafe Akka actor logging with thread-safe SLF4J logging in circuit breaker callbacks.

Root Cause

The CircuitBreaker.onOpen(), onClose(), and onHalfOpen() callbacks were using Akka Typed's context.log (ActorLogger). Since these callbacks execute on Future dispatcher threads rather than the actor's message-processing thread, and ActorLogger is not thread-safe with built-in actor-thread checks, log messages were silently dropped or errors were swallowed by the Future chain.

Changes

Updated three circuit breaker event callbacks in ElasticSearchClient.scala (lines 142-144) to use the existing object-level SLF4J logger instance instead of context.log:

• onOpen(): .onOpen(() => log.warn(...))
• onClose(): .onClose(() => log.info(...))
• onHalfOpen(): .onHalfOpen(() => log.info(...))

The log levels and message strings remain unchanged; only the logging mechanism was swapped. SLF4J's Logger is thread-safe and can be safely called from any thread.

Deployment

This is a standard code change with no operational requirements. It will be deployed through the normal CI/CD pipeline and does not require manual pipeline triggers, ECS redeployment commands, or infrastructure configuration changes.

Verification

After deployment, circuit breaker state transitions should now be visible in logs. CloudWatch Logs filter queries for "circuit breaker opened" will return results when the breaker trips.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 01d01d58-3e0e-4bec-abbb-7ec13e8655ff

📥 Commits

Reviewing files that changed from the base of the PR and between a5feba5 and 96fb075.

📒 Files selected for processing (1)

• src/main/scala/dpla/api/v2/search/ElasticSearchClient.scala

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Walkthrough

Updated CircuitBreaker event logging callbacks in ElasticSearchClient to use a shared SLF4J log instance instead of Akka Typed's context.log for onOpen, onClose, and onHalfOpen messages.

Changes

Cohort / File(s)	Summary
CircuitBreaker Logging src/main/scala/dpla/api/v2/search/ElasticSearchClient.scala	Replaced context.log with shared SLF4J log instance in CircuitBreaker event callbacks. Log levels and message content remain unchanged.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

Possibly related PRs

• Add Akka circuit breaker for ElasticSearch calls #105: Introduces the CircuitBreaker event handler callbacks (onOpen, onClose, onHalfOpen) whose logging mechanism is being refactored in this PR.

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately summarizes the main change: replacing Akka Typed's context.log with SLF4J logger in circuit breaker callbacks to fix missing state-transition logs.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/circuit-breaker-callback-logging

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