Introduction

Managing Lambda function updates in production often means walking a tightrope between delivering new features and maintaining stability. The default approach of swapping the image URI instantly exposes 100% of traffic to untested code, which is risky for mission-critical services.

What Happened

A scripted workflow steps in to eliminate guesswork. Using the AWS CLI, CodeDeploy, and a handful of strategic calls, you can publish an immutable version, shift traffic gradually, and halt immediately if anything breaks. The process begins by updating the function code, waiting for propagation, publishing a new version, and then handing traffic off via CodeDeploy.

Why This Matters

Beyond convenience, this approach introduces a safety net that the one-step update lacks. By publishing a version first, then shifting traffic in a controlled manner, you ensure that a faulty release only affects a subset of users or gets rolled back automatically. The script leverages Lambda versions as immutable snapshots and the LIVE alias as the stable traffic pointer.

Key Takeaways

  • The script requires three arguments: the Lambda function name, the CodeDeploy application name, and the new container image URI.
  • It uses set -e to fail fast, preventing traffic shifts to broken code.
  • Two AWS CLI waits ensure the function is fully updated and the new version is active before traffic moves.
  • CodeDeploy manages the alias shift, with configuration controlling whether the move is all-at-once, canary, or linear.
  • Prerequisites include an existing LIVE alias and a configured Main deployment group; the first deploy may need manual bootstrapping.

Conclusion

This script provides a solid starting point for automating versioned Lambda deployments within a CI/CD pipeline. It eliminates the need to manually track versions, publish snapshots, and shift traffic by hand, while still offering flexibility to tune deployment strategies to your risk tolerance.