Example of AWS AppConfig alongside the Serverless Framework for the use of Feature Flags

serverless.yml

service: serverless-feature-flag
provider:
  name: aws
  runtime: nodejs12.x
  lambdaHashingVersion: 20201221
  memorySize: 128
  stage: ${opt:stage, 'develop'}
  region: eu-west-1
  apiGateway:
    shouldStartNameWithService: true
  iamRoleStatements:
    - Effect: "Allow"
      Action:
        - appconfig:GetConfiguration
      Resource:
        - !Sub 'arn:aws:appconfig:${AWS::Region}:${AWS::AccountId}:application/${FeatureFlagApplication}'
        - !Sub 'arn:aws:appconfig:${AWS::Region}:${AWS::AccountId}:application/${FeatureFlagApplication}/environment/${FeatureFlagEnvironment}'
        - !Sub 'arn:aws:appconfig:${AWS::Region}:${AWS::AccountId}:application/${FeatureFlagApplication}/configurationprofile/${FeatureFlagAppConfigProfile}'
  environment:
    # app config specific
    AWS_APPCONFIG_EXTENSION_POLL_INTERVAL_SECONDS: 30
    AWS_APPCONFIG_EXTENSION_POLL_TIMEOUT_MILLIS: 3000
    AWS_APPCONFIG_EXTENSION_HTTP_PORT: 2772
    # application specific i.e. feature flag
    ENVIRONMENT: "feature-flag-environment"
    APPLICATION: "serverless-feature-flag-${self:provider.stage}"
    CONFIGURATION: "feature-flag-app-profile-${self:provider.stage}"
    STAGE: ${self:provider.stage}
package:
  individually: true
functions:
  feature:
    handler: src/handler.feature
    layers:
      - arn:aws:lambda:eu-west-1:434848589818:layer:AWS-AppConfig-Extension:41
    events:
      - http:
          path: feature
          method: get
resources:
  Resources:
    # the feature application
    FeatureFlagApplication:
      Type: AWS::AppConfig::Application
      Properties:
        Name: "serverless-feature-flag-${self:provider.stage}"
        Description: "Example serverless feature flag demo."
        Tags:
          - Key: App
            Value: "FeatureFlagApplication"
          - Key: Stage
            Value: "${self:provider.stage}"
    # the application environment
    FeatureFlagEnvironment:
      Type: AWS::AppConfig::Environment
      Properties:
        ApplicationId: !Ref FeatureFlagApplication
        Name: "feature-flag-environment"
        Description: "Feature Flag Environment"
        Tags:
          - Key: App
            Value: "FeatureFlagApplication"
          - Key: Stage
            Value: "${self:provider.stage}"
    # configuration profile
    FeatureFlagAppConfigProfile:
      Type: AWS::AppConfig::ConfigurationProfile
      Properties:
        ApplicationId: !Ref FeatureFlagApplication
        Name: "feature-flag-app-profile-${self:provider.stage}"
        LocationUri: "hosted"
    # configuration
    FeatureFlagConfigurationVersion:
      Type: AWS::AppConfig::HostedConfigurationVersion
      Properties:
        ApplicationId: !Ref FeatureFlagApplication
        ConfigurationProfileId: !Ref FeatureFlagAppConfigProfile
        Description: "Feature Flag Application Config"
        Content: !Sub |
          {
              "featureEnabled": true
          }
        ContentType: "application/json"
        LatestVersionNumber: 1
    # deployment strategy
    DeploymentStrategy:
      Type: AWS::AppConfig::DeploymentStrategy
      Properties:
        Name: "deployment-strategy-${self:provider.stage}"
        Description: "Feature flag deployment strategy ${self:provider.stage}"
        DeploymentDurationInMinutes: 0
        FinalBakeTimeInMinutes: 0
        GrowthFactor: 100
        GrowthType: LINEAR
        ReplicateTo: NONE
        Tags:
          - Key: App
            Value: "FeatureFlagApplication"
          - Key: Stage
            Value: "${self:provider.stage}"
    # deployment
    FeatureFlagDeployment:
      Type: AWS::AppConfig::Deployment
      Properties:
        ApplicationId: !Ref FeatureFlagApplication
        EnvironmentId: !Ref FeatureFlagEnvironment
        DeploymentStrategyId: !Ref DeploymentStrategy
        ConfigurationProfileId: !Ref FeatureFlagAppConfigProfile
        ConfigurationVersion: "1"
        Description: "feature flag deployment ${self:provider.stage}"
        Tags:
          - Key: App
            Value: "FeatureFlagApplication"
          - Key: Stage
            Value: "${self:provider.stage}"