Deployment strategies: versions, aliases and traffic shifting

Serverless Applications with AWS Lambda

Claudio Canales

Senior DevOps Engineer

Why deployment strategy matters

• Detect bugs quickly.
• Limit blast radius.
• Recover fast.

$LATEST vs published versions

$LATEST

• Moves every time you update code.

Versions

• Immutable snapshots.
• Easy to pin for rollbacks and traffic splitting.

A version is an immutable snapshot

• Treat versions like release artifacts.
• Each captures code and configuration.
• Once published, it doesn't change.
• You can always return to a known-good state.

Aliases are stable pointers

• A stable pointer.
• Invoke the alias instead of a version.
• Update where it points without changing callers.

Dev and prod aliases

• Great for environments.
• Move dev frequently.
• Promote to prod by moving the alias.

Traffic shifting with weighted aliases

• Test in production safely.
• Most traffic stays on the current version.
• A small percentage goes to the candidate.

Canary step 1: 90/10

• 90% stays on the current version.
• 10% tests the candidate under real load.
• Watch errors and latency.

Canary step 2: 50/50

• If the 10% slice looks good, increase the weight.
• 50% current, 50% candidate.
• Issues show up fast at 50/50.
• Monitoring matters.

Canary step 3: 100% new

• Route all traffic to the new version.
• The old version is still there.
• Rollback is simple.

Blue/green mental model

• Blue = current stable version.
• Green = new candidate version.
• Switch by moving the alias.
• Weighted routing makes the switch gradual.

Rollback = move the alias back

• No redeploy required.
• Move the alias to the last known-good version.
• Recover in seconds, not hours.
• Immutable versions and stable aliases work together.

Monitor during the shift

• Errors and timeouts.
• Duration and tail latency.
• Throttles if you use caps.
• Pause or roll back quickly.

Common pitfall: treating $LATEST as prod

• Relying on $LATEST loses predictability.
• Versions and aliases make it clear what's running.
• Rollbacks are safe.

Safe deploy checklist

• Publish a version.
• Shift traffic gradually with an alias.
• Monitor the results.
• Keep rollback ready at every step.

Key takeaways

• Versions give predictability.
• Aliases give stability.
• Weighted routing adds safety.
• Rollback = move the alias.

Let's practice!

Serverless Applications with AWS Lambda