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Read this on the main serverless docs site

AWS - Introduction

The Serverless Framework helps you develop and deploy your AWS Lambda functions, along with the AWS infrastructure resources they require. It's a CLI that offers structure, automation and best practices out-of-the-box, allowing you to focus on building sophisticated, event-driven, serverless architectures, comprised of Functions and Events.

The Serverless Framework is different from other application frameworks because:

  • It manages your code as well as your infrastructure
  • It supports multiple languages (Node.js, Python, Java, and more)

Core Concepts

Here are the Framework's main concepts and how they pertain to AWS and Lambda...

Functions

A Function is an AWS Lambda function. It's an independent unit of deployment, like a microservice. It's merely code, deployed in the cloud, that is most often written to perform a single job such as:

  • Saving a user to the database
  • Processing a file in a database
  • Performing a scheduled task

You can perform multiple jobs in your code, but we don't recommend doing that without good reason. Separation of concerns is best and the Framework is designed to help you easily develop and deploy Functions, as well as manage lots of them.

Events

Anything that triggers an AWS Lambda Function to execute is regarded by the Framework as an Event. Events are infrastructure events on AWS such as:

  • An AWS API Gateway HTTP endpoint request (e.g., for a REST API)
  • An AWS S3 bucket upload (e.g., for an image)
  • A CloudWatch timer (e.g., run every 5 minutes)
  • An AWS SNS topic (e.g., a message)
  • A CloudWatch Alert (e.g., something happened)
  • And more...

When you define an event for your AWS Lambda functions in the Serverless Framework, the Framework will automatically create any infrastructure necessary for that event (e.g., an API Gateway endpoint) and configure your AWS Lambda Functions to listen to it.

Resources

Resources are AWS infrastructure components which your Functions use such as:

  • An AWS DynamoDB Table (e.g., for saving Users/Posts/Comments data)
  • An AWS S3 Bucket (e.g., for saving images or files)
  • An AWS SNS Topic (e.g., for sending messages asynchronously)
  • Anything that can be defined in CloudFormation is supported by the Serverless Framework

The Serverless Framework not only deploys your Functions and the Events that trigger them, but it also deploys the AWS infrastructure components your Functions depend upon.

Services

A Service is the Framework's unit of organization. You can think of it as a project file, though you can have multiple services for a single application. It's where you define your Functions, the Events that trigger them, and the Resources your Functions use, all in one file entitled serverless.yml (or serverless.json or serverless.js). It looks like this:

# serverless.yml

service: users

functions: # Your "Functions"
  usersCreate:
    events: # The "Events" that trigger this function
      - http: post users/create
  usersDelete:
    events:
      - http: delete users/delete

resources: # The "Resources" your "Functions" use.  Raw AWS CloudFormation goes in here.

When you deploy with the Framework by running serverless deploy, everything in serverless.yml is deployed at once.

Plugins

You can overwrite or extend the functionality of the Framework using Plugins. Every serverless.yml can contain a plugins: property, which features multiple plugins.

# serverless.yml

plugins:
  - serverless-offline
  - serverless-secrets