Demo Serverless Deployments and Traffic Shifting With Lambda

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Lambda versioning basics

• Publishing a version creates an immutable snapshot of the function’s code and configuration.
• The special identifier \$LATEST is mutable — it always refers to the most recent un-published state (it changes whenever you update code or configuration).
• A qualified ARN (for example, arn:aws:lambda:us-east-1:598274344262:function:devops-020-320-function:6) targets a specific published version.
• Aliases are named pointers to versions (for example, prod, staging, live) and provide stable references for production invocations.

• Pin an alias to a single version (100% traffic to that version).
• Configure a weighted alias to split traffic between two versions (Lambda supports weights for up to two versions per alias).

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Quick CLI examples

• Publish a new version:

aws lambda publish-version --function-name devops-020-320-function --description "release v6"

• Create an alias that points to a specific version:

aws lambda create-alias --function-name devops-020-320-function --name prod --function-version 6 --description "Production"

• Create a weighted alias (90% to v6, 10% to v5):

aws lambda update-alias --function-name devops-020-320-function --name prod \
  --routing-config '{"AdditionalVersionWeights":{"5":0.1}}' --function-version 6

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Aliases and weighted traffic shifting

• Pin an alias to a single published version for stable traffic (example: prod -> 6).
• Split traffic between two versions via weights for gradual rollouts (example: prod -> 90% v6, 10% v5).

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When to use CodeDeploy for Lambda

• Built-in patterns: canary (small initial percentage), linear (incremental steps), and all-at-once.
• Lifecycle hooks: BeforeAllowTraffic and AfterAllowTraffic to run validation or smoke-tests.
• Alarm-based rollback: integrate CloudWatch alarms to trigger automatic rollbacks.
• Detailed deployment history, tags, and deployment-group management for traceability.

version: 0.0
Resources:
  - devops-demo-function:
      Type: AWS::Lambda::Function
      Properties:
        Name: "devops-demo-function"
        Alias: "prod"
        CurrentVersion: "5"
        TargetVersion: "6"
Hooks:
  BeforeAllowTraffic:
    - "arn:aws:lambda:us-east-1:123456789012:function:ValidateNewVersion"
  AfterAllowTraffic:
    - "arn:aws:lambda:us-east-1:123456789012:function:RunSmokeTests"

• BeforeAllowTraffic: run validations before new traffic is allowed.
• AfterAllowTraffic: run smoke tests after traffic starts flowing to the target.

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Practical tips and important limits

• Always invoke stable aliases in production instead of \$LATEST.
• Weighted aliases support at most two versions per alias. For multi-step rollouts, use CodeDeploy or manage multiple aliases programmatically.
• Use CodeDeploy for scheduled or automated canary/linear rollouts, hook execution, and alarm-based rollback.
• CloudWatch alarms can trigger rollbacks within CodeDeploy deployment configurations.
• AWS SAM and API Gateway also provide deployment/canary features — choose based on your pipeline and operational needs.
• Consider SnapStart (for supported runtimes like Java) or provisioned concurrency to reduce cold-start latency for heavy runtimes.

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Deployment patterns — quick comparison

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Summary — exam-relevant points

• \$LATEST is mutable and changes with every update; do not use it as a production reference.
• Aliases are stable references; use them for production traffic and auditability.
• Weighted aliases support at most two versions per alias for traffic splitting.
• Use CodeDeploy for automated canary/linear deployments, lifecycle hooks, and alarm-based rollback.
• Understand the differences between canary (small then full), linear (incremental), and all-at-once deployments.

• AWS Lambda versioning and aliases
• AWS CodeDeploy for Lambda applications
• CloudWatch alarms and metrics