AWS CDK CodePipeline without Synth/ShellStep

My AWS Project builds a Docker Image, pushes it to ECR and then deploys it to an ECS container.

The source code is on CodeCommit, and I already have two working CDK Stacks to 1) Build the Docker image, and 2) Deploy to ECS.

I would like to setup a pipeline via CDK. If I use the console, it is very straightforward to setup the pipeline adding the "Build" and "Deploy" stages defined by the stacks.

If I want to setup the pipeline via CDK, I could use a CDK Python code like this one:

# Create a source action for CodeCommit
source_action = cpactions.CodeCommitSourceAction(
            action_name="CodeCommit",
            output=codepipeline.Artifact("SourceArtifact")
            repository=codecommit.Repository(self, "SourceRepo",
                                             repository_name=SOURCE_GIT_REPOSITORY),
            branch=SOURCE_GIT_BRANCH
        )

# Create a ShellStep for the synth action (BUT I DO NOT NEED THIS!!!)
synth_action = pipelines.ShellStep("Synth",
                                   input=source_action.output,
                                   commands=[])

# Create a new CodePipeline
pipeline = pipelines.CodePipeline(self, PIPELINE_NAME,
                     pipeline_name=PIPELINE_NAME,
                     synth=synth_action, # THIS IS NOT OPTIONAL!
                     self_mutation=False)

# Add the build stage
pipeline.add_stage(BuildStage(self, "Build"))

# Add the deploy stage
pipeline.add_stage(DeployStage(self, "Deploy", env=kwargs['env']))

the problem is that the 'synth' parameter is required, but I definitely do not need it! What can I do to have my pipeline working without a "synth"? I just need to have source code, and then Build and Deploy stages.

What am I missing?

(BTW, the compiler complains that in the above code 'Build' action already exists, to underline that I did not understand the difference between 'Build' and 'Synth'...)

CodePipeline from pipelines package is used to build and deploy CDK applications. That's why it uses synth step. If you want to build and deploy docker image to ECR, you should use Pipeline construct from aws_codepipeline package. Check documentation for more details.