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cfn-cr-alb-rule

Cloudformation Custom Resource that creates a listener rule for an AWS ALB. The rule contains two actions. The first is an authentication action; the second rule forwards to a target group, containing only a single instance, if the first rule succeeds.

Inventory of source code and supporting files:

  • ruler - Code for the application's Lambda function.
  • events - Invocation events that you can use to invoke the function.
  • tests - Unit tests for the application code.
  • template.yaml - A template that defines the application's AWS resources.

The AWS SAM CLI is used to build and package the lambda code. The sceptre utility is used to deploy the macro that invokes the lambda as a CloudFormation stack.

Use in a Cloudformation Template

In addition to creating the ALBListenerRule custom resource, also required is a target group with a single target, the EC2 instance. It is necessary to create the target group so that the ALB can route to the instance if authentication succeeds.

Here's an example, inserted into a stack that contains an AWS::EC2::Instance resource with the Logical ID LinuxInstance. It also refers to several other resources defined outside:

  • VpcId: this uses an imported value from the VPC that is home to the ALB
  • ServiceToken: this uses the Lambda function ARN
  • ListenerArn: the ARN of a listener created for the ALB
  EC2TargetGroup:
    Type: AWS::ElasticLoadBalancingV2::TargetGroup
    Properties:
      Name: !Sub 'TargetGroup-${LinuxInstance}'
      HealthCheckIntervalSeconds: 30
      HealthCheckProtocol: HTTP
      HealthCheckTimeoutSeconds: 15
      HealthyThresholdCount: 5
      Matcher:
        HttpCode: '200'
      Port: 443
      Protocol: HTTPS
      TargetGroupAttributes:
      - Key: deregistration_delay.timeout_seconds
        Value: '20'
      Targets:
      - Id: !Ref LinuxInstance
        Port: 443
      UnhealthyThresholdCount: 3
      VpcId: !ImportValue
        'Fn::Sub': '${AWS::Region}-${VpcName}-VPCId'
      Tags:
      - Key: Name
        Value: !Sub 'TargetGroup-${LinuxInstance}'
  AlbListenerRule:
    Type: Custom::ALBListenerRule
    Properties:
      ServiceToken: !ImportValue
        'Fn::Sub': '${AWS::Region}-cfn-cr-alb-rule-FunctionArn'
      InstanceId: !Ref LinuxInstance
      TargetGroupArn: !Ref EC2TargetGroup
      ListenerArn: 'arn:aws:elasticloadbalancing:us-east-1:465877038949:listener/app/sc135-poc/bf54cc972d64237b/8ad4c71091181c60'

The creation of the custom resource triggers the lambda. The lambda makes several AWS API calls in order to create a listener rule. First, it pulls a secret key from AWS System Manager for the OIDC client. Second, it pulls all existing rules to calculate the priority. Finally, it creates the rule with the actions as described above.

Development

Contributions

Contributions are welcome.

Setup Development Environment

Install the following applications:

Install Requirements

Run pipenv install --dev to install both production and development requirements, and pipenv shell to activate the virtual environment. For more information see the pipenv docs.

After activating the virtual environment, run pre-commit install to install the pre-commit git hook.

Update Requirements

First, make any needed updates to the base requirements in Pipfile, then use pipenv to regenerate both Pipfile.lock and requirements.txt.

$ pipenv update --dev

We use pipenv to control versions in testing, but sam relies on requirements.txt directly for building the lambda artifact, so we dynamically generate requirements.txt from Pipfile.lock before building the artifact. The file must be created in the CodeUri directory specified in template.yaml.

$ pipenv requirements > ruler/requirements.txt

Additionally, pre-commit manages its own requirements.

$ pre-commit autoupdate

Create a local build

Use a Lambda-like docker container to build the Lambda artifact

$ sam build --use-container

Run unit tests

Tests are defined in the tests folder in this project, and dependencies are managed with pipenv. Install the development dependencies and run the tests using coverage.

$ pipenv run coverage run -m pytest tests/ -svv

Automated testing will upload coverage results to Coveralls.

Run integration tests

Running integration tests requires docker

$ sam local invoke ALBListenerRuleFunction --event events/event.json

Deployment

Build

sam build

Deploy Lambda to S3

This requires the correct permissions to upload to bucket bootstrap-awss3cloudformationbucket-19qromfd235z9 and essentials-awss3lambdaartifactsbucket-x29ftznj6pqw

sam package --template-file .aws-sam/build/template.yaml \
  --s3-bucket essentials-awss3lambdaartifactsbucket-x29ftznj6pqw \
  --output-template-file .aws-sam/build/cfn-cr-alb-rule.yaml

aws s3 cp .aws-sam/build/cfn-cr-alb-rule.yaml s3://bootstrap-awss3cloudformationbucket-19qromfd235z9/cfn-cr-alb-rule/master/

Install Lambda into AWS

Create the following sceptre file, changing the parameters to match the values for your OIDC client.

config/prod/cfn-cr-alb-rule.yaml

template:
  type: "http"
  url: "https://s3.amazonaws.com/bootstrap-awss3cloudformationbucket-19qromfd235z9/cfn-cr-alb-rule/master/cfn-cr-alb-rule.yaml"
stack_name: "cfn-cr-alb-rule"
parameters:
  OidcClientSecretKeyName: '/alb-notebook-access/AuthenticateOidcClientSecret'
  OidcIssuer: 'https://repo-prod.prod.sagebase.org/auth/v1'
  OidcAuthorizationEndpoint: 'https://signin.synapse.org'
  OidcTokenEndpoint: 'https://qtg2zn2bbf.execute-api.us-east-1.amazonaws.com/token'
  OidcUserInfoEndpoint: 'https://repo-prod.prod.sagebase.org/auth/v1/oauth2/userinfo'
  OidcClientId: '100050'
  SessionCookieNamePrefix: 'AWSELBAuthSessionCookie'
  SessionTimeout: 3600
  KmsDecryptPolicyArn: !stack_output_external sc-kms-key::KmsDecryptPolicyArn

Install the lambda using sceptre:

sceptre --var "profile=my-profile" --var "region=us-east-1" launch prod/cfn-cr-alb-rule.yaml

Author

Tess Thyer; Principal Data Engineer, Sage Bionetworks