Lambda: runtime must be Runtime.FROM_IMAGE when using image asset for Lambda function

[LajosPolya]

Describe the bug

Neither aws_lambda.Handler.FROM_IMAGE nor cdk.aws_lambda.Runtime.FROM_IMAGE resolve when deploying a lambda using the aws_lambda.Code.fromDockerBuild.

They produce the following errors:

1. "Error: handler must be Handler.FROM_IMAGE when using image asset for Lambda function"
   and
2. "Error: runtime must be Runtime.FROM_IMAGE when using image asset for Lambda function"

Expected Behavior

Neither aws_lambda.Handler.FROM_IMAGE nor cdk.aws_lambda.Runtime.FROM_IMAGE should produce an error when deploying a lambda using the aws_lambda.Code.fromDockerBuild.

Current Behavior

Neither aws_lambda.Handler.FROM_IMAGE nor cdk.aws_lambda.Runtime.FROM_IMAGE resolve when deploying a lambda using the aws_lambda.Code.fromDockerBuild.

Note that I was able to resolve the first error but replacing cdk.aws_lambda.Handler.FROM_IMAGE with the string "Handler.FROM_IMAGE".

I wasn't able to resolve the runtime error this way since FunctionProps.runtime is of type Runtime not string.

Reproduction Steps

I have a repo to repsoduce the steps (use this exact commit since it's not the most recent commit):
LajosPolya/aws-cdk-templates@b92f222

Possible Solution

The interesting this about this is that both cdk.aws_lambda.Runtime.FROM_IMAGE and cdk.aws_lambda.Handler.FROM_IMAGE resolve correctly when using aws_lambda.Code.fromEcrImage instead of aws_lambda.Code.fromDockerBuild.

I have an example in this repo:
https://github.com/LajosPolya/aws-cdk-templates/tree/main/deploy-lambda-from-ecr

Another interesting fact about this is I'm able to deploy the Lambda successfully if I set the runtime to cdk.aws_lambda.Runtime.NODEJS_20_X and the handler to "index.handler". This seems to go against what the docs say: "Use Handler.FROM_IMAGE when defining a function from a Docker image."

This can be reproduced here:
LajosPolya/aws-cdk-templates@fc76814

Additional Information/Context

This bug was already opened once but was never fixed:
#25758

CDK CLI Version

2.133.0 (build dcc1e75)

Framework Version

No response

Node.js Version

v20.11.1

OS

Windows 10

Language

TypeScript

Language Version

"typescript": "~5.3.3"

Other information

No response

[pahud]

Let's simplify the code. I guess you should use

    const dockerImageCode = lambda.Code.fromDockerBuild(
      path.join(__dirname, '../docker-function.d')
    );

    const fn = new lambda.Function(this, 'Fn', {
      runtime: lambda.Runtime.FROM_IMAGE,
      code: dockerImageCode,
      handler: lambda.Handler.FROM_IMAGE,
    });

But if you look at the source code here, DockerImageFunction is generally recommended in your use case.

aws-cdk/packages/aws-cdk-lib/aws-lambda/lib/image-function.ts

Lines 63 to 75 in 87139ab

	/**
	* Create a lambda function where the handler is a docker image
	*/
	export class DockerImageFunction extends Function {
	constructor(scope: Construct, id: string, props: DockerImageFunctionProps) {
	super(scope, id, {
	...props,
	handler: Handler.FROM_IMAGE,
	runtime: Runtime.FROM_IMAGE,
	code: props.code._bind(props.architecture),
	});
	}
	}

Why not just use DockerImageFunction in your use case?

[LajosPolya]

I wasn't aware of this option. I was able to test this and it works! Thanks for the suggestion @pahud

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