DevOpsMay 21, 2026 — 5 min read

Fixing a Flaky CI/CD Pipeline: A Debugging Diary

A pipeline that fails 1 in 10 times isn't a minor annoyance. It's a trust problem that erodes team velocity.

James TurnerDevOps Consultant

CI/CDDevOpsReliability

Fixing a Flaky CI/CD Pipeline: A Debugging Diary

Overview

A client's pipeline was passing most of the time, which made the failures harder to diagnose than a pipeline that failed consistently. Intermittent issues like this tend to get worked around rather than fixed — until they can't be ignored anymore.

Article

The symptom vs. the cause

Developers had started re-running failed builds automatically, assuming flakiness was unavoidable. That masked the real issue: a race condition in a shared test database that only surfaced under parallel test execution.

Isolating the variable

We disabled test parallelization temporarily to confirm the hypothesis, then moved to isolated, ephemeral test databases per build rather than a shared instance. Failures dropped to near zero within a week.

Preventing the next one

We added pipeline health monitoring that flags re-run rates, not just failure rates, since a high re-run rate is often the earliest signal of a flaky pipeline before anyone complains about it directly.

Key takeaways

›Track re-run rates, not just failure rates, to catch flakiness early
›Shared test infrastructure is a common source of intermittent failures
›Isolate variables methodically rather than guessing at root cause
›Ephemeral, per-build resources eliminate a whole class of race conditions