use aws `cdk synth` output via cloudformation

8
votes

I am working in an environment with existing Cloudformation based pipelines. I am wondering if it's possible to describe my infrastructure in CDK and then generate the Cloudformation to be used in the pipeline with no changes to the pipelines. I want the fact that I use CDK to be completely transparent.

3
amazon-web-servicesamazon-cloudformationaws-cdk
If i understood your question you are asking about pipeline which will run cdk synth grab the yaml the generated and use it as template ? – Amit Baranes
I meant to run cdk synth before the commit, locally, possibly as a Git precommit hook 🙈 I don't have possibility of changing the pipeline, so the fact of using cdk instead of cloudformation would have to be transparent to the pipeline – sumek
It's possible, i have an example using code build and code pipeline. code build listen to git repo when commit created new build started compile cdk and run cdk synth, later code pipeline deploy cdk stack. i guess you want to change to second part to your cloudformation based pipeline. does is it sounds a possible solution for you ? – Amit Baranes
keep in mind that, depending on your cdk stack, its not easily possible to call create-stack on a synthesized template because of CfnParameters which cant be resolved without some workarounds. – Logemann

3 Answers

5
votes

I would generally not recommend to use the output of cdk synth via CloudFormation except you know what you are doing very well.

Here is the reason why: There are some edge cases in which the CDK does bootstrapping and asset publishing in advance, e.g. for so called asset sources (docker images, s3 files, etc).

The topic has some overlap with issues in the CDK repository on GitHub asking about CI/CD integration. [1]

There is work in progress to develop a fully automated CI/CD process for the CDK [2]. The so called cloud assembly [3] contains all resources which are necessary to deploy via CloudFormation but as the RFC points out:

The cloud assembly includes a CloudFormation template for each stack and asset sources (docker images, s3 files, etc) that must be packaged and published to the asset store in each environment that consumes them.

If you are not using any assets or have the option to package and deploy them before using CloudFormation, using cdk synth output should be possible in CloudFormation when supplying the correct CFN params (as others have already pointed out in this thread).

References

[1] https://github.com/aws/aws-cdk/issues/6894
[2] https://github.com/aws/aws-cdk-rfcs/blob/master/text/0049-continuous-delivery.md
[3] https://github.com/aws/aws-cdk/blob/master/packages/@aws-cdk/cloud-assembly-schema/README.md

2
votes

Yes, it is possible. I have a process which uses the CDK to 'build' the CloudFormation template using cdk synth. This template is then uploaded into an S3 bucket on a versioned path.

You can then deploy the CloudFormation template from the bucket using the --template-url option on create-stack.

https://docs.aws.amazon.com/cli/latest/reference/cloudformation/create-stack.html

0
votes

The output of cdk synth can be stored in a json.

build_spec=BuildSpec.from_object({
                "version": "0.2",
                "run-as": "root",
                "phases": {
                    "install": {
                        "commands": [
                            'npm install -g aws-cdk',
                            'pip install -r requirements.txt',
                        ]
                    },
                    "build": {
                        "commands": [
                            'cdk synth stack-dev --verbose --debug=true -o > output.json'
                        ]
                    }
                },
                "artifacts": {
                    "files": "output.json"
                },
            })

            cdk_build_action = CodeBuildAction(
            action_name="CDKBuild",
            project=cdk_build,
            input=source_artifact,
            outputs=[cdk_build_output]
        )

This json can be forwarded to deploy stage with CloudFormationCreateUpdateStackAction CloudFormationCreateUpdateStackAction(template_path=cdk_build_output.at_path("output.json"))