Canary Deployments

Shift a small slice of traffic to a new version, watch metrics, then ramp up — or roll back automatically if alarms fire. Limits blast radius compared to all-at-once cutovers.

flowchart LR
  T[Traffic] --> A{Alias}
  A -->|90%| V1[v1 stable]
  A -->|10%| V2[v2 new]
  V2 -.alarm fires.-> RB[Auto rollback to v1]

Lambda — Alias Traffic Shifting

• Publish an immutable version; point an alias (e.g. prod) at it.
• The alias splits weighted traffic between two versions (routing-config).
• Combine with CodeDeploy for automated, monitored shifts.

# Send 10% of prod traffic to the new version
aws lambda update-alias \
  --function-name my-fn --name prod \
  --function-version 42 \
  --routing-config '{"AdditionalVersionWeights":{"43":0.1}}'

CodeDeploy Deployment Configs

• Canary — Canary10Percent5Minutes: 10% for 5 min, then 100%.
• Linear — Linear10PercentEvery1Minute: +10% on an interval.
• AllAtOnce — immediate cutover (use for dev only).
• Pre/Post-traffic hooks (Lambda) run validation; CloudWatch alarms trigger automatic rollback.

SAM / Serverless Framework

# AWS SAM
AutoPublishAlias: prod
DeploymentPreference:
  Type: Canary10Percent5Minutes
  Alarms:
    - !Ref MyFnErrorAlarm

References

• Implementing Canary Deployments of AWS Lambda Functions with Alias Traffic Shifting
• Serverless plugin: git@github.com:davidgf/serverless-plugin-canary-deployments.git

Related

Other progressive strategies: blue/green (two full environments, swap), rolling (replace instances in batches). Canary is blue/green with a metered ramp.