AWS Lambda Shift Canary Traffic Across Two Versions

arazzo: 1.0.1
info:
  title: AWS Lambda Shift Canary Traffic Across Two Versions
  summary: Read an alias, split its invocations between the current version and a canary version by weight, and read the routing back to confirm it took.
  description: >-
    The traffic-weighting half of a Lambda canary deploy, kept separate from
    publishing so a rollout can be dialled up or rolled back without cutting new
    versions. An alias points at one primary version and can additionally route a
    weighted share of invocations to a second version. This workflow reads the
    alias to capture its RevisionId, applies the caller's weight map under that
    guard, and reads the alias back so the routing Lambda actually stored is
    visible rather than assumed. Dialling a canary back to zero is the same call
    with an empty weight map. Every step spells out its request inline so the
    flow can be read and executed without opening the underlying OpenAPI
    description.
  version: 1.0.0
sourceDescriptions:
- name: aliasesApi
  url: ../openapi/aws-lambda-aliases-api-openapi.yml
  type: openapi
workflows:
- workflowId: canary-traffic-shift
  summary: Re-weight an existing alias between its primary version and a canary version.
  description: >-
    Resolves the alias, updates its primary version and additional version
    weights under a RevisionId guard, and verifies the stored routing
    configuration.
  inputs:
    type: object
    required:
    - functionName
    - aliasName
    - primaryVersion
    - additionalVersionWeights
    properties:
      functionName:
        type: string
        description: The name or ARN of the function whose alias is being re-weighted.
      aliasName:
        type: string
        description: The alias carrying production traffic (e.g. prod).
      primaryVersion:
        type: string
        description: >-
          The version the alias points at, which receives all invocations not
          claimed by additionalVersionWeights.
      additionalVersionWeights:
        type: object
        description: >-
          Map of version number to the share of invocations it receives, between
          0.0 and 1.0 (e.g. {"7": 0.1} sends 10 percent to version 7 and leaves
          90 percent on primaryVersion). Lambda supports one additional version.
          Pass an empty object to send all traffic back to primaryVersion.
      shiftDescription:
        type: string
        description: Description recorded against the alias for this shift (e.g. "canary 10%").
  steps:
  - stepId: resolveAlias
    description: >-
      Read the alias to capture the version it currently points at and its
      RevisionId, which guards the update against a concurrent release.
    operationId: getAlias
    parameters:
    - name: FunctionName
      in: path
      value: $inputs.functionName
    - name: AliasName
      in: path
      value: $inputs.aliasName
    successCriteria:
    - condition: $statusCode == 200
    outputs:
      currentVersion: $response.body#/FunctionVersion
      currentRouting: $response.body#/RoutingConfig
      aliasRevisionId: $response.body#/RevisionId
  - stepId: applyWeights
    description: >-
      Set the primary version and the weighted split in a single update.
      AdditionalVersionWeights is replaced wholesale, so an empty map removes the
      canary and returns every invocation to the primary version.
    operationId: updateAlias
    parameters:
    - name: FunctionName
      in: path
      value: $inputs.functionName
    - name: AliasName
      in: path
      value: $inputs.aliasName
    requestBody:
      contentType: application/json
      payload:
        FunctionVersion: $inputs.primaryVersion
        Description: $inputs.shiftDescription
        RevisionId: $steps.resolveAlias.outputs.aliasRevisionId
        RoutingConfig:
          AdditionalVersionWeights: $inputs.additionalVersionWeights
    successCriteria:
    - condition: $statusCode == 200
    outputs:
      aliasArn: $response.body#/AliasArn
      pointsAtVersion: $response.body#/FunctionVersion
      revisionId: $response.body#/RevisionId
  - stepId: verifyRouting
    description: >-
      Read the alias back so the routing configuration Lambda stored is observed
      directly, confirming the canary is carrying the intended share before the
      rollout proceeds.
    operationId: getAlias
    parameters:
    - name: FunctionName
      in: path
      value: $inputs.functionName
    - name: AliasName
      in: path
      value: $inputs.aliasName
    successCriteria:
    - condition: $statusCode == 200
    outputs:
      verifiedPrimaryVersion: $response.body#/FunctionVersion
      verifiedRouting: $response.body#/RoutingConfig
      verifiedRevisionId: $response.body#/RevisionId
  outputs:
    previousVersion: $steps.resolveAlias.outputs.currentVersion
    previousRouting: $steps.resolveAlias.outputs.currentRouting
    primaryVersion: $steps.verifyRouting.outputs.verifiedPrimaryVersion
    routingConfig: $steps.verifyRouting.outputs.verifiedRouting