Debugging production workflows can be difficult, especially when failures occur due to unexpected or non-deterministic behaviour. Traditional logging or assumptions often do not provide enough confidence to identify the exact root cause.

One tool that has been extremely helpful for me is the Cadence Workflow Replayer.

Instead of guessing, I download the workflow execution history from production and replay it locally in debug mode. This allows me to reproduce the exact failure scenario and inspect execution step-by-step.

Why workflow replay works

Cadence workflows must be deterministic.

During replay:

• The workflow code executes again locally.
• Activity results are loaded from recorded history instead of being executed again.
• Any divergence between history and current workflow logic results in deterministic errors.

This makes replay ideal for debugging workflow logic issues.

Problems replay helped me solve

Common issues I resolved using replay:

• Non-deterministic workflow errors
• Nil pointer crashes
• Logic mismatches between versions

Replay gives strong proof during root cause analysis because it reproduces the exact execution path.

When NOT to use replay

Replay validates workflow logic only.

It is not useful when:

• The bug exists inside activity implementation.