Back to blog
Jun 13, 2024
3 min read

Projen with own batteries

How to setup a projen project to store central decisions to apply across all own repositories

Use case

As described here [Use cdk-notifier to compare changes in pull requests]({{ site.baseurl }}/aws/cdk/2023/12/16/cdk-notifier-feature-stacks.html), the cdk-notifier displays the diff between the feature branch and the main branch. In case of using tags in the CDK there a two ways to tag resources, which will have different consequences in the diff output of the cdk-notifier.

Tagging with Tags.of()

The documentation of CDK describes the tagging of resources with the Tags.of() method: https://docs.aws.amazon.com/cdk/v2/guide/tagging.html This could look like this:

Tags.of(app).add("branch", branchName);

https://github.com/JohannesKonings/cdk-notifier-examples/blob/746c2b2bc0ecc0ecf3e8f0e6ff771a7430a45d04/src/main.ts#L23

The tag will then be added to all resources in the synthesized cloudformation template.

{
 "Resources": {
  "TableCD117FA1": {
   "Type": "AWS::DynamoDB::Table",
   "Properties": {
    "AttributeDefinitions": [
     {
      "AttributeName": "id",
      "AttributeType": "S"
     }
    ],
    "BillingMode": "PAY_PER_REQUEST",
    "KeySchema": [
     {
      "AttributeName": "id",
      "KeyType": "HASH"
     }
    ],
    "TableName": "Table-tags-tags-of",
    "Tags": [
     {
      "Key": "branch",
      "Value": "tags-tags-of"
     }
    ]
   },
   ...
  }
 }
}

Because the tag is in the template, it will then be shown in the diff.

![diff tag of]({{ site.baseurl }}/img/2024-04-20-cdk-notifier-and-tags/diff-tag-of.png)

https://github.com/JohannesKonings/cdk-notifier-examples/pull/5

Tagging with stack properties

The other way is to pass the tags as stack properties (https://docs.aws.amazon.com/cdk/api/v2/docs/aws-cdk-lib.Stack.html#tags-1). This could look like this:

new CdkNotfifierFeatureStackExample(
  app,
  `cdk-notifier-feature-stacks-${branchName}`,
  {
    tags: {
      branch: branchName,
    },
  }
);

https://github.com/JohannesKonings/cdk-notifier-examples/blob/66874c06b8204b09781e9ad3ab8707590b948000/src/main.ts#L23

The tag will then be added to the stack properties and not to the template file.

{
 "Resources": {
  "TableCD117FA1": {
   "Type": "AWS::DynamoDB::Table",
   "Properties": {
    "AttributeDefinitions": [
     {
      "AttributeName": "id",
      "AttributeType": "S"
     }
    ],
    "BillingMode": "PAY_PER_REQUEST",
    "KeySchema": [
     {
      "AttributeName": "id",
      "KeyType": "HASH"
     }
    ],
    "TableName": "Table-tags-stack-properties",
   },
   ...
  }
 }
}

In cdk.out the tags are only in the manifest.json file.

{
  "version": "36.0.0",
  "artifacts": {
    "cdk-notifier-feature-stacks-tags-stack-properties.assets": {
      "type": "cdk:asset-manifest",
      "properties": {
        "file": "cdk-notifier-feature-stacks-tags-stack-properties.assets.json",
        "requiresBootstrapStackVersion": 6,
        "bootstrapStackVersionSsmParameter": "/cdk-bootstrap/hnb659fds/version"
      }
    },
    "cdk-notifier-feature-stacks-tags-stack-properties": {
      "type": "aws:cloudformation:stack",
      "environment": "aws://unknown-account/unknown-region",
      "properties": {
        "templateFile": "cdk-notifier-feature-stacks-tags-stack-properties.template.json",
        "terminationProtection": false,
        "tags": {
          "branch": "tags-stack-properties"
        },
        "validateOnSynth": false,
        ...
      }
    }
  }
}

Then it will not be shown in the diff, and the cdk-notifier skip the pull request comment.

check the diff to main
Deploying with stack postfix main
Stack cdk-notifier-feature-stacks-main
Hold on while we create a read-only change set to get a diff with accurate replacement information (use --no-change-set to use a less accurate but faster template-only diff)
There were no differences

  Number of stacks with differences: 0

create cdk-notifier report
BRANCH_NAME: tags-stack-properties
GITHUB_OWNER: JohannesKonings
GITHUB_REPO: $(echo JohannesKonings/cdk-notifier-examples | cut -d'/' -f2)
time="2024-04-20T14:59:48Z" level=info msg="There is no diff detected for tag id diff-to-main. Skip posting diff."

https://github.com/JohannesKonings/cdk-notifier-examples/actions/runs/8765869174/job/24057331666#step:6:55

Conclusion

If you want to see the tags in the diff output of the cdk-notifier, you should use the Tags.of() method to tag the resources. If not, you can go with the stack properties.

Code

https://github.com/JohannesKonings/cdk-notifier-examples