cdk.lambda.DockerImageFunction: add ability to set image tag as parameter

[mdvertola]

Describe the feature

On the lambda DockerImageFunction construct, it would be sweet if there was an ability to set the image tag.
for example:

const createKnowledgeIndexLambda = new lambda.DockerImageFunction(
      this,
      `CreateKnowledgeIndexLambda`,
      {
        code: lambda.DockerImageCode.fromImageAsset(
          "lambda/knowledge/create_knowledge_index"
        ),
        timeout: cdk.Duration.minutes(5),
        imageTag: "latest"
      }
    );

Use Case

When running several docker lambda functions in a stack or set of stacks, the amount of images starts to pile up in ECR because each image gets automatically tagged with a unique id.

Now I am aware that ECR retention policies can be created to automatically clear out old images but since these containers are tagged with unique IDs, it is difficult to create a policy that would, for example: clear out all images without a tag that are greater than 14 days old.

Proposed Solution

Add the ability to set the imageTag as a parameter of the dockerImageFunction construct to something static/developer-defined. During deployment, set the image tag to the parameter defined in the construct.

From my knowledge of ECR, I believe this is how the workflow would play out:

• CDK deployment creates image with the tag defined in construct (eg latest)
• if there is an existing image tagged latest, ECR should automatically just untag that image
• This way we will be left with one image tagged latest and n images without a tag

I think that doing this would enable the ability to set a more straightforward ECR retention policy. Or hey honestly, it might just be easier/ better to just remove the old image if the new one builds successfully so this pile-up of images doesn't happen.

Other Information

Definitely just taking a stab here at something I found a little annoying when working on some projects so I'm not sure if this was abstracted away or done for a reason someone much smarter than myself has a solid design decision around but either way wanted to throw it out there to see if we could get this on the map.

Thanks!

Acknowledgements

• I may be able to implement this feature request
• This feature might incur a breaking change

CDK version used

latest

Environment details (OS name and version, etc.)

macOS 13.0

[pahud]

CDK publishes the container image assets with its hash as the tag and does not allow users to specify a static image tag for the assets AFAIK.

I guess we'll need an external construct to create ECR lifecycle policies to remove unused images or layers.

I am leaving this a p2 feature request. Please help us with upvotes to prioritize.