Serverless Top Tips

- 3 minutes read - 463 words

Tip 1: Packaging of aws-sdk

The aws-sdk comes bundled with the Lambda execution environment, but you should not rely on this. Instead you should pack the aws-sdk in your deployment package because:

  1. the one in the Lambda execution environment is always a few months old, so probably missing patches, security updates, etc.
  2. it’ll introduce difference to what I had tested
  3. AWS can update it without notice, so far I haven’t heard of anyone running into issues in Node.js. But a while back a lot of people’s Python functions started failing without any user action because AWS updated the version of boto3 in the environment, and that version had a bug.
  4. It made no difference to the cold start performance where I load the AWS SDK from, it’s the act of requiring it that incurs latency.
  5. The AWS SDK is not that big and makes a trivial difference to the time it takes to deploy.

It’s also the recommendation from AWS - to pack your own AWS SDK.

Tip 2: Don’t require the full aws-sdk if not needed

The AWS developer docs use the following as an example:

// Load the AWS SDK for Node.js
const AWS = require('aws-sdk');

// Create DynamoDB document client
const docClient = new AWS.DynamoDB.DocumentClient();

This has the result of initialising the whole of the SDK as opposed to just the service which can be done as follows:

const DynamoDB = require('aws-sdk/clients/dynamodb')
const documentClient = new DynamoDB.DocumentClient()

The example above saves 141ms in initialisation time, or a whopping 33% reduction.

See Yan Cui - how expensive is the full aws sdk

Tip 3: Use webpack for functions

Webpack is described as a static module bundler for Javascript. When webpack processes your application, it internally builds a dependency graph which maps every module your project needs and generates one or more bundles. At a high level, it means you can significantly reduce function size, as it only pulls in the relevant code that is needed. I decided to use Serverless Webpack as a plugin to the Serverless Framework.

To start off with, install the following:

$ npm install webpack --save-dev
$ npm install webpack-node-externals --save-dev
$ npm install serverless-webpack --save-dev

The next step is to include the plugin and the configuration of the plugin in the serverless.yml file:

plugins:
  - serverless-webpack
...
custom:
  webpack:
    webpackConfig: 'webpack.config.js'   # Name of webpack configuration file
    includeModules: false   # Node modules configuration for packaging
    packager: 'npm'   # Packager that will be used to package your external modules

By default the plugin looks for a webpack.config.js in the service directory. I used the following basic configuration:

module.exports = {
    entry: {
      'functions/index': './functions/index.js',
      'functions/data/getNextQuestion': './functions/data/get-question.js',
      'functions/constants/constants': './functions/constants/constants.js',
    },
    mode: 'production',
    target: 'node'
  }

The resulted in the package size reducing from 8MB to less than 1MB.