cdk-typescript-tooling

AWS is great. Lambdas changed the way we think about programming. CDK makes it all even better.

Nonetheless, working with these technologies we've encountered some pain points. We want to address a few of them in this package.

• streamlining build of TypeScript code
• speeding up the development feedback loop with lambda updates
• streamlined/shared error logging
• "smart defaults" for exposing lambdas through http

CDK TypeScript resource

Why?

All-typescript codebase including infrastructure as a code with CDK and application code is a pleasure to use. Deployment of it, not so much.

You can transpile your code to a new directory, copy package.json there, install production dependencies, and then have CDK send that whole folder to lambda. It's painful to set up, and it will bring a ton of unnecessary code (everything in node_modules) along. Webpack is better - it can take an entrypoint and create a small bundled file that includes only what you need. Unfortunately, no one likes to set up complex and diverging webpack configurations, especially in a monorepo with tens if not hundreds of tiny packages.

What?

We wanted TypeScript Lambda experience to be seamless - if a developer wants to create a new function, he should create a typescript file, add it to CDK and that's it. Now you can do it like so:

import { TypeScriptFunction } from "cdk-typescript-tooling";
// ...
const statusHandle = new TypeScriptFunction(scope, "Purchase-Status-Endpoint", {
  entry: require.resolve("@sales/purchase-endpoint/src/handler.ts"),
});

It takes all the parameters that you know from @aws-cdk/aws-lambda, like runtime, environment, timeout, and so on, because we extend it.

Instant updates (development)

Why?

Deploying the whole stack everytime when you want to check your changes is tiresome and boring. If you do it by pushing to CI system - it's even slower. If you do it locally, it's still slow. And if your build relies on multiple secrets (like most do), you can't even do it properly from your local dev. Changing files in-line through lambda panel is painful - you can't paste TypeScript code because that will result in Syntax Errors. You also risk forgetting about some changes in the code, and later losing them after the next push, or - even worse - QAing and approving the functionality and merging to master, even though the code in repository does not have the required fix. It's a mess :)

What?

Using the TypeScriptFunction from our tool gives you the ability to use update-typescript-function command.

Updating all functions:

Assuming your stack is declared at ./src/cdk.ts Run it like this:

npx update-typescript-function ./src/cdk.ts

And it will quickly and automatically update all TypeScript Lambda functions found in your CDK Stack.

Configuration:

Actually, you might need to do a few exports first... ;-)

export AWS_SECRET_ACCESS_KEY=SECRET_ACCESS_KEY
export AWS_ACCESS_KEY_ID=ACCESS_KEY
export AWS_REGION=us-east-2

In the future we do want to read those from ~/.aws/credentials, but for now please export the values.

We need your cdk file to export a stack, in most cases you will do something like this:

import * as cdk from "@aws-cdk/core";
import { SalesSystem } from "./SalesSystem";

const baseStackName = "SalesSystemExample";
export default new SalesSystem(new cdk.App(), baseStackName);

If you need to do something async before returning a stack, a pattern like this should work:

export default (async () => {
  const stackSuffix = await getStackSuffix(baseStackName);
  return new SalesSystem(new cdk.App(), `${baseStackName}${stackSuffix}`);
})();

We like to deploy a stack per branch, so all our branches have different StackNames and also differently named (suffixed) resources. Because of that we rely on branch name to cache your stack information. Worst case scenario you will have cache built multiple times with the same data.

Updating single function:

The compilation and uploading of functions happen in parallel. Because of that it is crazy fast (<10 s for ~20 functions) and in most cases that is what you should be doing. It comes with the advantage that if you change a code that's used by a few different functions, all of them will be redeployed. Sometimes you might not realize that some piece of code is used in multiple places and get yourself in some weird inconsistent state. But if you must, or if you have hundreds of functions in the stack, it's simple, get the Logical ID of a function (using aws cli or going to the stack using their cloudformation panel), and do:

npx update-typescript-function ./src/cdk.ts PurchaseEndpointIKYULFRNR9VJ

Error logging

Why?

Having multiple independent lambda functions is great, but it comes with a price of difficult monitoring. We like to be notified of things going wrong, as early as possible and in automated fashion. New lambda functions should be connected to the system with a minimal setup.

What?

Our TypeScriptFunction has built-in ability to send Error logs to a passed lambda handler. First, create a logHandler:

import { CloudWatchLogsDecodedData, CloudWatchLogsHandler } from "aws-lambda";
import zlib from "zlib";

export const handler: CloudWatchLogsHandler = async (event, context) => {
  const compressedPayload = Buffer.from(event.awslogs.data, "base64");
  const jsonPayload = zlib.gunzipSync(compressedPayload).toString("utf8");
  const parsed: CloudWatchLogsDecodedData = JSON.parse(jsonPayload);
  console.log(parsed);
};

This is the simplest possible one that will just log errors in a CloudWatch stream aggregating all errors from all lambda functions.

Now in your cdk define a TypeScriptFunction that will deploy that code. Assign its handle to a variable.

import { SubscriptionFilter, FilterPattern } from "@aws-cdk/aws-logs";
import * as LogsDestinations from "@aws-cdk/aws-logs-destinations";
//...
const logHandle = new TypeScriptFunction(scope, "logHandler", {
  entry: require.resolve("@sales/logHandler/src/handler.ts"),
});

Pass it to existing function like so:

new TypeScriptFunction(scope, "Purchase-Status-Endpoint", {
  entry: require.resolve("@sales/purchase-endpoint/src/handler.ts"),
  logFunction: logHandle,
});

Now, whenever any error (console.error or exception) shows up in the Purchase-Status-Endpoint, it will be passed and displayed by the logHandler. Obviously, the usefulness of that increases with the number of lambdas you have. :-)

Enjoy!

Easily expose through HTTP

Why?

In our development exposing lambdas with http is a very frequent case. The code around it for most cases stays exactly the same and increases the noise. We define the function:

const handler = new TypeScriptFunction(stack, "Add-Function", {
  entry: require.resolve("@calculator/add/src/handler.ts"),
});

Add HttpApi using LambdaProxyIntegration

const statusApi = new apiGateway2.HttpApi(stack, "PurchaseStatusHttpApi", {
  defaultIntegration: new apiGateway2Integrations.LambdaProxyIntegration({
    handler,
  }),
});

Add the url to CfnOutput to, among others, see the url in CI/CD logs.

new CfnOutput(stack, "addUrl", {
  value: statusApi.url,
});

What?

Define your function with withHttp option like so:

new TypeScriptFunction(stack, "Add-Function", {
  entry: require.resolve("@calculator/add/src/handler.ts"),
  withHttp: true,
});

...and the other two steps will be done for you automatically.

State of the project

This is a Proof Of Concept. It works for us, and you can play around with it using this Demo Repo: xolvio/aws-sales/system-example
Please let us know if you hit any problems. Please do NOT use the updater for updating your production code. That should be a no-go even after this project becomes battle-tested.