Introduction

SAH was born with the intention of facilitating the rollbacks of functions in serverless projects, making use of the aliases in associated projects we can perform a rollback in a much faster way, without the need to redeploy using a stack.

Alias

A Lambda alias is a pointer to a function version that you can update. When you deploy a new version, you can update the alias to use the new version, or split traffic between two versions. See Create an alias for a Lambda function

Let's review how it works with the current serverless framework flow, with a basic configuration we can have a running function.

service: aws-python-rest-api

frameworkVersion: '3'

provider:
  name: aws
  runtime: python3.8

functions:
  hello:
    handler: handler.hello
    events:
      - http:
          path: /
          method: get

In AWS Cloudformation we would have the following stack:

CloudFormationTemplate

AWSTemplateFormatVersion: '2010-09-09'
Description: The AWS CloudFormation template for this Serverless application
Resources:
  ServerlessDeploymentBucket:
    Type: AWS::S3::Bucket
    Properties:
      BucketEncryption:
        ServerSideEncryptionConfiguration:
        - ServerSideEncryptionByDefault:
            SSEAlgorithm: AES256
  ServerlessDeploymentBucketPolicy:
    Type: AWS::S3::BucketPolicy
    Properties:
      Bucket:
        Ref: ServerlessDeploymentBucket
      PolicyDocument:
        Statement:
        - Action: s3:*
          Effect: Deny
          Principal: "*"
          Resource:
          - Fn::Join:
            - ''
            - - 'arn:'
              - Ref: AWS::Partition
              - ":s3:::"
              - Ref: ServerlessDeploymentBucket
              - "/*"
          - Fn::Join:
            - ''
            - - 'arn:'
              - Ref: AWS::Partition
              - ":s3:::"
              - Ref: ServerlessDeploymentBucket
          Condition:
            Bool:
              aws:SecureTransport: false
  HelloLogGroup:
    Type: AWS::Logs::LogGroup
    Properties:
      LogGroupName: "/aws/lambda/aws-python-rest-api-dev-hello"
  IamRoleLambdaExecution:
    Type: AWS::IAM::Role
    Properties:
      AssumeRolePolicyDocument:
        Version: '2012-10-17'
        Statement:
        - Effect: Allow
          Principal:
            Service:
            - lambda.amazonaws.com
          Action:
          - sts:AssumeRole
      Policies:
      - PolicyName:
          Fn::Join:
          - "-"
          - - aws-python-rest-api
            - dev
            - lambda
        PolicyDocument:
          Version: '2012-10-17'
          Statement:
          - Effect: Allow
            Action:
            - logs:CreateLogStream
            - logs:CreateLogGroup
            - logs:TagResource
            Resource:
            - Fn::Sub: arn:${AWS::Partition}:logs:${AWS::Region}:${AWS::AccountId}:log-group:/aws/lambda/aws-python-rest-api-dev*:*
          - Effect: Allow
            Action:
            - logs:PutLogEvents
            Resource:
            - Fn::Sub: arn:${AWS::Partition}:logs:${AWS::Region}:${AWS::AccountId}:log-group:/aws/lambda/aws-python-rest-api-dev*:*:*
      Path: "/"
      RoleName:
        Fn::Join:
        - "-"
        - - aws-python-rest-api
          - dev
          - Ref: AWS::Region
          - lambdaRole
  HelloLambdaFunction:
    Type: AWS::Lambda::Function
    Properties:
      Code:
        S3Bucket:
          Ref: ServerlessDeploymentBucket
        S3Key: serverless/aws-python-rest-api/dev/1727612825604-2024-09-29T12:27:05.604Z/aws-python-rest-api.zip
      Handler: handler.hello
      Runtime: python3.8
      FunctionName: aws-python-rest-api-dev-hello
      MemorySize: 1024
      Timeout: 6
      Role:
        Fn::GetAtt:
        - IamRoleLambdaExecution
        - Arn
    DependsOn:
    - HelloLogGroup
  HelloLambdaVersionP8UAvh48AIJQ7pb2vPXamLWuIzfvJ5UVnkjBIee8CU:
    Type: AWS::Lambda::Version
    DeletionPolicy: Retain
    Properties:
      FunctionName:
        Ref: HelloLambdaFunction
      CodeSha256: Cow3ahBjOjSbQ8EHUWOZIzOk6f4Sf50opPeYFGX4J4M=
  ApiGatewayRestApi:
    Type: AWS::ApiGateway::RestApi
    Properties:
      Name: dev-aws-python-rest-api
      EndpointConfiguration:
        Types:
        - EDGE
      Policy: ''
  ApiGatewayMethodGet:
    Type: AWS::ApiGateway::Method
    Properties:
      HttpMethod: GET
      RequestParameters: {}
      ResourceId:
        Fn::GetAtt:
        - ApiGatewayRestApi
        - RootResourceId
      RestApiId:
        Ref: ApiGatewayRestApi
      ApiKeyRequired: false
      AuthorizationType: NONE
      Integration:
        IntegrationHttpMethod: POST
        Type: AWS_PROXY
        Uri:
          Fn::Join:
          - ''
          - - 'arn:'
            - Ref: AWS::Partition
            - ":apigateway:"
            - Ref: AWS::Region
            - ":lambda:path/2015-03-31/functions/"
            - Fn::GetAtt:
              - HelloLambdaFunction
              - Arn
            - "/invocations"
      MethodResponses: []
    DependsOn:
    - HelloLambdaPermissionApiGateway
  ApiGatewayDeployment1727612823481:
    Type: AWS::ApiGateway::Deployment
    Properties:
      RestApiId:
        Ref: ApiGatewayRestApi
      StageName: dev
    DependsOn:
    - ApiGatewayMethodGet
  HelloLambdaPermissionApiGateway:
    Type: AWS::Lambda::Permission
    Properties:
      FunctionName:
        Fn::GetAtt:
        - HelloLambdaFunction
        - Arn
      Action: lambda:InvokeFunction
      Principal: apigateway.amazonaws.com
      SourceArn:
        Fn::Join:
        - ''
        - - 'arn:'
          - Ref: AWS::Partition
          - ":execute-api:"
          - Ref: AWS::Region
          - ":"
          - Ref: AWS::AccountId
          - ":"
          - Ref: ApiGatewayRestApi
          - "/*/*"
Outputs:
  ServerlessDeploymentBucketName:
    Value:
      Ref: ServerlessDeploymentBucket
    Export:
      Name: sls-aws-python-rest-api-dev-ServerlessDeploymentBucketName
  HelloLambdaFunctionQualifiedArn:
    Description: Current Lambda function version
    Value:
      Ref: HelloLambdaVersionP8UAvh48AIJQ7pb2vPXamLWuIzfvJ5UVnkjBIee8CU
    Export:
      Name: sls-aws-python-rest-api-dev-HelloLambdaFunctionQualifiedArn
  ServiceEndpoint:
    Description: URL of the service endpoint
    Value:
      Fn::Join:
      - ''
      - - https://
        - Ref: ApiGatewayRestApi
        - ".execute-api."
        - Ref: AWS::Region
        - "."
        - Ref: AWS::URLSuffix
        - "/dev"
    Export:
      Name: sls-aws-python-rest-api-dev-ServiceEndpoint

As we can see we do not have aliases associated to our functions, the aliases work as pointers to specific versions of a function, this allows us to manage more easily our versions without the need to update the stack of that project as the serverless rollback command currently does.

serverless rollback --timestamp timestamp

With SAH we can easily create these aliases in our serverless project in this way if we want to rollback to a previous version we just need to configure the alias to point to this.

SAH Plugin

This is a serverless plugin that allow create aliases without imposing a way-of-working with them.

• Create an "ACTIVE" alias, and using that alias in API Gateway, Event Sources and Event Rules.
• Connect your deployments with the SAH application.

GitHub Repository

SAH App

This application will facilitate the management of your alias pointing to the version you need easily either manually or with the information provided by your deployments.

• Create projects from a stack.
• Easily monitor your functions, deployments and versions.

GitHub Repository