Supplemental Templates for AWS CloudFormation

Ambassador is an active user of the excellent aws-cf-templates and cfn-modules templates (link below) provided by widdix. In a few cases, we've needed features that weren't supported by the core repository. This repo shares these templates back to the community (until and unless they're integrated into the core).

Templates

This package includes the following templates

Fargate: `service`, `cluster-alb-target`

The core package offers two ways to expose a service, at least one of them is required: through a cloudmap and through an ALB. We had background services that needed neither and foreground services that needed both. The fargate/service template in this package (also PR #362) accepts configurations for all or none of these service registries, automatically reconfiguring the service based on the presence or absence of parameters.

The template is basically a drop-in replacement for fargate/service-cloudmap except that I renamed ParentClientStack to ParentCloudMapIngressStack and Name to CloudMapName to better link the parameter to the feature (could be reverted).

To replicate the behavior of the existing fargate/service-cluster-alb, a user would combine fargate/service with the new fargate/cluster-alb-target shim:

   Service:
 	Type: 'AWS::CloudFormation::Stack'
 	Properties:
 	  Parameters:
 		...
 		ParentALBTargetStack: !GetAtt 'ServiceALBTarget.Outputs.StackName'
 		...
 	  TemplateURL: 'aws-cf-templates/fargate/service.yaml'
   ServiceALBTarget:
 	Type: 'AWS::CloudFormation::Stack'
 	Properties:
 	  Parameters:
 		...
 	  TemplateURL: 'aws-cf-templates/fargate/cluster-alb-target.yaml'

If needed, one could could create a shim for service-dedicated-alb as well.

Cloudmap RDS Postgres

While most of our services use the CNAME for our RDS postgres server directly, we had two cases where we needed to expose the RDS server at a known address:

During the migration, so we could make and test smaller changes.
A legacy library that forces us to hard-code these kinds of parameters

This template creates a cloudmap entry for the database at the specified subdomain (e.g. db.<local>):

  CloudMapDB:
    Type: 'AWS::CloudFormation::Stack'
    Properties:
      Parameters:
        ParentCloudMapStack: !GetAtt 'CloudMap.Outputs.StackName'
        CloudMapHost: 'db'
        RdsPostgresStack: !GetAtt 'Database.Outputs.StackName'
      TemplateURL: './ambsw-cf-templates/state/cloudmap-rds-postgres.yaml'

Step Function: Fargate Task with Retry

Our current best practice for migrations are step functions that run migrations in ECS Tasks. This template demonstrates a state machine that runs the task and report success or failure. Since we were using DockerHub images, we often experienced a CannotPullContainerError that indicated some sort of pull error. Since this was not a real failure, the state machine is configured to retry in response to this error. WARNING: Obviously this template cannot distinguish a case where the error is due to a legitimate problem like a container that does not exist.

Fargate Task

To support out migration Step Function, we also need a definition for a Fargate Task. This extracts the key Resources from Fargate Service (exposing the same Parameters) so they can be used in other instances like this.

Related projects

aws-cf-templates

The core repository with Free Templates for AWS CloudFormation.

Learn more: https://github.com/widdix/aws-cf-templates

cfn-modules

Rapid CloudFormation: Modular, production ready, open source also by widdix.

Learn more: https://github.com/cfn-modules/docs

cfn-modules-shims

When Ambassador needed features that weren't available in aws-cf-templates, we looked to the related cfn-moduels library. Since the interfaces for objects are dissimilar, we developed a variety of shims to make it easier to share resources across the two libraries.

Learn more: https://github.com/ambsw/cfn-modules-shims/

License

All templates are published under Apache License Version 2.0.

About

Ambassador Software Works develops and delivers EMR-integrated healthcare applications for hospitals and vendors. The company's marquee APEXamenity product uses predictive analytics to identify patients at a high risk for poor experience. Hospital staff (usually Nurse Leaders) leverage these insights to provide targeted mitigation efforts.

ambsw/ambsw-cf-templates