[lambda-nodejs] Deploy additional files alongside bundled output

I want to be able to push up some additional files along with the bundled output. One way of doing this would be to expose a hook that allows augmenting the bundling commands.

Use Case

I’m trying to deploy a lambda function that uses the Prisma database client. They have a guide using the serverless cli to deploy to lambda but I was hoping to use cdk since I have other infrastructure to manage as well.

The prisma database client is generated based on a schema.prisma file that itself is generated by introspecting the database. It actually automatically performs this generation on install, so my hope was that I could

• Specify nodeModules: ["@prisma/client", "@prisma/cli"]
• Bundle up the rest of the function and dependencies
• When install occurs, the client get generated as normal

The problem is that the schema.prisma file isn’t copied to the output directory and I don’t think there’s a way for me to accomplish that. Ideally I would like to make use of the bundling functionality while still having some control over what else gets deployed.

Proposed Solution

Perhaps expose a hook to inject custom commands? This is the area of interest. I got something working hacking around node_modules where all I need to do is insert a cp schema.prisma ${options.outputDir} in between parcelCommand and depsCommand. So I was thinking a function like this:

const fn = new lambda.NodejsFunction(this, "MyCDKFunction", {
  nodeModules: ["@prisma/client", "@prisma/cli"],
  handler: "handler",
  entry: "lib/index.ts",
  modifyBundleCommand: ({ parcelCommand, depsCommand, options }) => {
    return [parcelCommand, `cp schema.prisma ${options.outputDir}`, depsCommand];
  }   
});

The default would just be ({ parcelCommand, depsCommand }) => [parcelCommand, depsCommand] to maintain the default behavior.

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

---

This is a 🚀 Feature Request

[jogold]

We could have something like this:

Add a additionalCommands prop of type ICommand:

interface ICommand {
  beforeBundling(outputDir: string): string;
  afterBundling(outputDir: string): string;
}

new lambda.NodejsFunction(this, "MyFunction", {
  // ...
  additionalCommands: {
    beforeBundling(outputDir: string): string {
      // return a command to run before bundling
      // it can use the `outputDir` to copy to the right output folder
    },
    afterBundling(outputDir: string): string {
      // return a command to run after bundling
    },
  }
})

[jogold]

Quick question: Isn’t the outputDir always equal to /asset-output

Not when doing local bundling https://github.com/aws/aws-cdk/tree/master/packages/%40aws-cdk/aws-lambda-nodejs#local-bundling