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• Trying to replay activity

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 Workflow Replayer present in Cadence and Temporal.

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. My demo include example for cadence, but temporal is very similar

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.

When to use replay

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