Flaky OTLP Traces Test: Address Already In Use

by Alex Johnson 47 views

We've encountered a flaky test within the OpenTelemetry (otel-arrow) project. Specifically, the validation::otlp::tests::test_otlp_traces_single_request test failed in a recent build. This issue appears to be intermittent, as rerunning the job resolved the problem. This write-up serves as a record of the incident for future reference and potential investigation.

Incident Details

Error Message

The core of the failure points to an "address already in use" error, indicating a conflict when the otelarrowcol collector tries to bind to a specific TCP port (127.0.0.1:60988).

FAIL [ 0.027s] (613/692) otap-df-pdata validation::otlp::tests::test_otlp_traces_single_request
stdout ---

 running 1 test
 test validation::otlp::tests::test_otlp_traces_single_request ... FAILED

 failures:

 failures:
 validation::otlp::tests::test_otlp_traces_single_request

 test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured; 263 filtered out; finished in 0.01s

stderr ---
[Collector stderr] 2025-12-05T14:00:15.279Z info otelconftelemetry/metrics.go:25 Internal metrics telemetry disabled {"resource": {"service.instance.id": "c0952c14-9977-4b01-8769-6582293b964c", "service.name": "otelarrowcol", "service.version": "0.45.0"}}
[Collector stderr] 2025-12-05T14:00:15.280Z info service@v0.140.0/service.go:224 Starting otelarrowcol... {"resource": {"service.instance.id": "c0952c14-9977-4b01-8769-6582293b964c", "service.name": "otelarrowcol", "service.version": "0.45.0"}, "Version": "0.45.0", "NumCPU": 4}
[Collector stderr] 2025-12-05T14:00:15.280Z info extensions/extensions.go:40 Starting extensions... {"resource": {"service.instance.id": "c0952c14-9977-4b01-8769-6582293b964c", "service.name": "otelarrowcol", "service.version": "0.45.0"}}
[Collector stderr] 2025-12-05T14:00:15.281Z error graph/graph.go:439 Failed to start component {"resource": {"service.instance.id": "c0952c14-9977-4b01-8769-6582293b964c", "service.name": "otelarrowcol", "service.version": "0.45.0"}, "error": "listen tcp 127.0.0.1:60988: bind: address already in use", "type": "Receiver", "id": "otlp"}
[Collector stderr] 2025-12-05T14:00:15.281Z info service@v0.140.0/service.go:261 Starting shutdown... {"resource": {"service.instance.id": "c0952c14-9977-4b01-8769-6582293b964c", "service.name": "otelarrowcol", "service.version": "0.45.0"}}
[Collector stderr] 2025-12-05T14:00:15.281Z info extensions/extensions.go:68 Stopping extensions... {"resource": {"service.instance.id": "c0952c14-9977-4b01-8769-6582293b964c", "service.name": "otelarrowcol", "service.version": "0.45.0"}}
[Collector stderr] 2025-12-05T14:00:15.281Z info service@v0.140.0/service.go:275 Shutdown complete. {"resource": {"service.instance.id": "c0952c14-9977-4b01-8769-6582293b964c", "service.name": "otelarrowcol", "service.version": "0.45.0"}}
[Collector stderr] Error: cannot start pipelines: failed to start "otlp" receiver: listen tcp 127.0.0.1:60988: bind: address already in use
[Collector stderr] 2025/12/05 14:00:15 collector server run finished with error: cannot start pipelines: failed to start "otlp" receiver: listen tcp 127.0.0.1:60988: bind: address already in use

thread 'validation::otlp::tests::test_otlp_traces_single_request' (19940) panicked at crates/pdata/src/validation/scenarios.rs:34:13:
Test failed: ChannelClosed { source: RecvError(()) }
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

Possible Causes and Mitigation

The "address already in use" error typically arises when another process is already listening on the same port. In the context of automated testing environments, this can occur due to:

  1. Port contention: Multiple tests or processes might be attempting to start the otelarrowcol collector on the same port concurrently. This is especially common in parallel test execution scenarios.
  2. Resource leakage: A previous test run might have failed to properly shut down the collector, leaving the port occupied.
  3. Environmental Issues: Sometimes the test environment can have unforeseen configurations which leads to the collision of ports.

To mitigate this flakiness, consider the following strategies:

  • Implement port randomization: Configure the tests to use a dynamically assigned port for the OTLP receiver. This reduces the likelihood of conflicts.
  • Ensure proper shutdown: Add robust shutdown logic to the test setup and teardown to guarantee that the collector is terminated and the port is released after each test run. Use Try...Finally blocks to ensure that shutdown logic will execute even when there is a failure.
  • Introduce retry mechanisms: If a port binding error occurs, retry the test a few times before declaring it a failure. This can help overcome transient port contention issues. Introduce an exponential backoff strategy to avoid overwhelming the system with retries.
  • Increase test isolation: Explore options for running tests in isolated environments (e.g., containers) to minimize interference between tests.
  • Resource limits: Review the resource limit configurations to ensure the tests can get the resources they need.

Investigating the Root Cause

To gain a deeper understanding of the issue, further investigation may involve:

  • Analyzing test logs: Examine the logs for other tests running concurrently to identify potential port conflicts.
  • Monitoring resource usage: Track CPU, memory, and network utilization during test execution to detect resource bottlenecks.
  • Debugging the test environment: Inspect the test environment configuration for any factors that might contribute to port contention.

Conclusion

The validation::otlp::tests::test_otlp_traces_single_request test exhibited a flaky failure due to an "address already in use" error. While rerunning the job resolved the issue, addressing the underlying cause is crucial for maintaining the reliability of the OpenTelemetry (otel-arrow) project's test suite. Implementing the mitigation strategies outlined above can help reduce the frequency of these failures and improve the overall testing experience. This issue highlights the challenges of testing in concurrent environments and the importance of robust resource management.

For more information on OpenTelemetry and related topics, you can visit the official OpenTelemetry website.