What tracking down missing TCP Keepalives taught me about Docker, Golang, and GitLab

A GitLab Runner issue that began with a static analysis failure led to a complex investigation uncovering a bug in the Docker client library, eventually resolved by upgrading the Go compiler. The problem involved silent test failures in GitLab's automated test infrastructure, causing productivity issues due to lack of output when errors occurred. The investigation revealed that changes in TCP keepalive settings and live CI trace feature flags were not the culprits, pointing instead to differences between Docker Machine and Docker executors. The issue was linked to Google Cloud Platform's 10-minute idle timeout affecting Docker Machine executors, which could be mitigated by adjusting sleep commands in the CI configuration. Attempts to monitor and decrypt network traffic between the GitLab Runner and Docker container were initially thwarted by HTTPS encryption and perfect forward secrecy, requiring modifications to disable specific cipher suites for effective debugging.

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