Serverless Handbook

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Elements of serverless – lambdas, queues, gateways, and more

Serverless is about combining small elements into a whole. But what are the elements and how do they fit together?

We mentioned lambdas, queues, and a few other in previous chapters – Architecture Principles and Serverless Flavors. Let's see how they work.

Lambda – a cloud function

"Lambda" comes from lambda calculus – a mathematical definition of functional programming that Alonzo Church introduced in the 1930s. It's an alternative to Turing's turing machines. Both describe a system that can solve any solvable problem. Turing machines use iterative step-by-step programming, lambda calculus uses functions-calling-functions programming.

Both are equal in power.

AWS named their cloud functions AWS Lambda. As the platform grew in popularity, the word "lambda" morphed into a generic term for cloud functions. The core building block of serverless computing.

A lambda is a function. In this context, a function running as its own tiny server triggered by an event.

Here's a lambda function that returns "Hello world" in response to an HTTP request.

// src/handler.ts

import { APIGatewayEvent } from "aws-lambda";

export const handler = async (event: APIGatewayEvent) => {
    return {
        statusCode: 200
        body: "Hello world"

The TypeScript file exports a function called handler. The function accepts an event and returns a response. The AWS Lambda platform handles the rest.

Because this is a user-facing API method, it accepts an AWS API Gateway event and returns an HTTP style response. Status code and body.

Other providers and services have different events and expect different responses. A lambda always follows this pattern 👉 function with an event and a return value.

Considerations with lambda functions

Your functions should follow functional programming principles:

  • idempotent – multiple calls with the same inputs produce the same result
  • pure – rely on the arguments you're given and nothing else. Your environment does not persist, data in local memory might vanish.
  • light on side-effects – you need side-effects to make changes like writing to a database. Make sure those come in the form of calling other functions and services. State inside your lambda does not persist
  • do one thing and one thing only – small functions focused on one task are easiest to understand and combine

Small functions work together to produce extraordinary results. Like this example of combining Twilio and AWS Lambda to answer the door.

Creating lambdas

In the open source Serverless Framework, you define lambda functions with serverless.yml like this:

    handler: dist/helloworld.handler
      - http:
          path: helloworld
          method: GET
          cors: true

Define a helloworld function and say it maps to the handler method exported from dist/helloworld. We're using a build step for TypeScript – the code is in src/, we run it from dist/.

events lists the triggers that run this function. An HTTP GET request on the path /helloworld in our case.

Other typical triggers include Queues, S3 changes, CloudWatch events, and DynamoDB listeners. At least on AWS.


Queue is short for message queue – a service built on top of queue, the data structure. Software engineers aren't that inventive with names 🤷‍♂️

You can think of the queue data structure as a list of items.


enqueing adds items to the back of a queue, dequeing takes them out the front. Items in the middle wait their turn. Like a lunch-time burrito queue. First come first serve, FIFO for short (first in first out).

Hello! 👋

Are you a frontend engineer diving into backend? Do you have just that one bit of code that can't run in the browser? Something that deals with secrets and APIs?

That's what cloud functions are for my friend. You take a JavaScript function, run it on serverless, get a URL, and voila.

But that's easy mode. Any tutorial can teach you that.

What happens when you wanna build a real backend? When you want to understand what's going on? Have opinions on REST vs GraphQL, NoSQL vs. SQL, databases, queues, talk about performance, cost, data processing, deployment strategies, developer experience?


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Dive into modern backend. Understand any backend

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With digital + paperback content Serverless Handbook has been more than 1 year in development. Lessons learned from 14 years of building production grade websites and webapps.

With Serverless Handbook, Swiz teaches the truths of distributed systems – things will fail – but he also gives you insight on how to architect projects using reliability and resilience perspectives so you can monitor and recover.

~ Thai Wood, author of Resilience Roundup

If you want to understand backends, grok serverless, or just get a feel for modern backend development, this is the book for you.

Serverless Handbook full of color illustrations, code you can try, and insights you can learn. But it's not a cookbook and it's not a tutorial.

Serverless Handbook on your bookshelf
Serverless Handbook on your bookshelf

Yes, there's a couple tutorials to get you started, to show you how it fits together, but the focus is on high-level concepts.

Ideas, tactics, and mindsets that you need. Because every project is different.

The Serverless Handbook takes you from your very first cloud function to modern backend mastery. In the words of an early reader:

Serverless Handbook taught me high-leveled topics. I don't like recipe courses and these chapters helped me to feel like I'm not a total noob anymore.

The hand-drawn diagrams and high-leveled descriptions gave me the feeling that I don't have any critical "knowledge gaps" anymore.

~ Marek C, engineer

If you can JavaScript, you can backend.

Plus it looks great on your bookshelf 😉

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