How to add more steps before CDK Pipelines' synth step?

Question

Hello,

I'm working on a application deployed as a CDK Application, and I'm looking to leverage AWS CDK Pipelines for CI/CD automation.

I have multiple modules in my application, and before the synthesis phase, I need to build the source code of each module. I want these build operations to be performed in parallel for efficiency.

The examples provided in the CDK Pipeline documentation only demonstrate that it can be configured via "synth" property.
```
    const pipeline = new pipelines.CodePipeline(this, 'Pipeline', {
      synth: new pipelines.ShellStep('Synth', {
        input: pipelines.CodePipelineSource.connection('my-org/my-app', 'main', {
          connectionArn: 'arn:aws:codestar-connections:us-east-1:222222222222:connection/7d2469ff-514a-4e4f-9003-5ca4a43cdc41', // Created using the AWS console * });',
        }),
        commands: [
          'npm ci',
          'npm run build',
          'npx cdk synth',
        ],
      }),
    });
```

How can one extend CDK Pipelines with additional stage that can be run before "synth"  and perform necessary operations on the source code - build, unit testing etc., ideally in parallel, and the output will serve as an input to the "synth" step ?

The pipeline should look something like on the picture.
*Build* stage is created by Pipeline and I would like to add a custom *ModuleBuild* stage where I can perform necessary build steps for each module.
![Enter image description here](/media/postImages/original/IM9JRtUgJiSRmwuJPrMN8iKw)

Thanks

Accepted Answer

Found solution myself. Posting the answer here in case it might be useful.

**Option 1**

It is possible to do it by using an existing pipeline as described in the documentation.
[https://docs.aws.amazon.com/cdk/api/v2/docs/aws-cdk-lib.pipelines-readme.html#using-an-existing-aws-codepipeline](https://docs.aws.amazon.com/cdk/api/v2/docs/aws-cdk-lib.pipelines-readme.html#using-an-existing-aws-codepipeline)

One can create _pre Synth_ stages and have more fine grained control over the build process.

Example from the documentation:

```
declare const codePipeline: codepipeline.Pipeline;

const sourceArtifact = new codepipeline.Artifact('MySourceArtifact');

const pipeline = new pipelines.CodePipeline(this, 'Pipeline', {
  codePipeline: codePipeline,
  synth: new pipelines.ShellStep('Synth', {
    input: pipelines.CodePipelineFileSet.fromArtifact(sourceArtifact),
    commands: ['npm ci','npm run build','npx cdk synth'],
  }),
});
```

**Option 2**

It turned out that _additionalInputs_  accept __Step__ as a source.
It is mentioned in the documentation as well

[https://docs.aws.amazon.com/cdk/api/v2/docs/aws-cdk-lib.pipelines-readme.html#synth-and-sources](https://docs.aws.amazon.com/cdk/api/v2/docs/aws-cdk-lib.pipelines-readme.html#synth-and-sources)

Example from the documentation:

```
const prebuild = new pipelines.ShellStep('Prebuild', {
  input: pipelines.CodePipelineSource.gitHub('myorg/repo1', 'main'),
  primaryOutputDirectory: './build',
  commands: ['./build.sh'],
});

const pipeline = new pipelines.CodePipeline(this, 'Pipeline', {
  synth: new pipelines.ShellStep('Synth', {
    input: pipelines.CodePipelineSource.gitHub('myorg/repo2', 'main'),
    additionalInputs: {
      'subdir': pipelines.CodePipelineSource.gitHub('myorg/repo3', 'main'),
      '../siblingdir': prebuild,
    },

commands: ['./build.sh'],
  })
});
```

_Option 2_ is what I ended up with since it looks cleaner.

Answer

Hi, cdk --build option seems to be what you are looking for

See https://github.com/aws/aws-cdk/commit/eb9b8e23906e2e1375f45f795d71b905bc0a52af

Or type 'cdk build --help' on your laptop

How to add more steps before CDK Pipelines' synth step?

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