This section is not necessary to complete the workshop, but we recommend that you take the time to see how cdk watch can speed up your personal deployments.

CDKTF Watch #

The watch command is experimental, so you should only use it in development environments. It also automatically deploys all changes without asking for confirmation.

We can do better than calling cdktf deploy each time. cdktf watch is similar to cdktf deploy except that instead of being a one-shot operation, it monitors your code and assets for changes and attempts to perform a deployment automatically when a change is detected.

Once we set it up, we can use cdktf watch --auto-approve to detect changes that require full Terraform apply.

Modify your cdktf.json file #

When the cdktf watch command runs, the files that it observes are determined by the "watchPattern" setting in the cdktf.json file. the watchPattern expects an array of glob patterns, e.g. ["main.ts", "../constructs/**/*.ts", "lib/*.ts"]. See the configure files to watch section of configuration file overview.

Your cdktf.json file should look similar to this:

{
  "language": "typescript",
  "app": "npx ts-node main.ts",
  // ...
  "watchPattern": [
    "./**/*.ts",
  ]
}

As you can see, the sample app comes with a suggested "watchPattern" setting. We do in fact want to observe our .js files in the lambda folder, so let’s add "lambda/*.js" to the list:

{
  "language": "typescript",
  "app": "npx ts-node main.ts",
  // ...
  "watchPattern": [
    "./**/*.ts",
    "lambda/*.js",
  ]
}

Now you’re all set to start watching!

Running cdktf watch #

First, call cdktf watch:

Due to its potential destructive behaviour, you have to explicitely set the --auto-approve flag.

cdktf watch --auto-approve

This will trigger an initial deployment and immediately begin observing the files we’ve specified in cdktf.json.

Let’s change our lambda asset code in lambda/hello.js one more time:

exports.handler = async function(event) {
  console.log("request:", JSON.stringify(event, undefined, 2));
  return {
    statusCode: 200,
    headers: { "Content-Type": "text/plain" },
    body: `Good Night, CDKTF! You've hit ${event.path}\n`
  };
};

Once you save the changes to your Lambda code file, cdktf watch will recognize that your file has changed and trigger a new deployment.

Wrap Up #

The rest of this tutorial will continue using cdktf deploy instead of cdktf watch. But if you want to, you can simply keep cdktf watch on. If you need to make a full deployment, cdktf watch will call cdktf deploy for you.

For a deeper dive on cdktf watch use cases, read Increasing Development Speed with CDKTF Watch.