docker-lambda

A sandboxed local environment that replicates the live AWS Lambda environment almost identically – including installed software and libraries, file structure and permissions, environment variables, context objects and behaviors – even the user and running process are the same.

You can use it for testing your functions in the same strict Lambda environment, knowing that they'll exhibit the same behavior when deployed live. You can also use it to compile native dependencies knowing that you're linking to the same library versions that exist on AWS Lambda and then deploy using the AWS CLI.

This project consists of a set of Docker images for each of the supported Lambda runtimes (Node.js 0.10 and 4.3, Python 2.7* and Java 8*) – as well as build images that include packages like gcc-c++, git, zip and the aws-cli for compiling and deploying.

There's also an npm module to make it convenient to invoke from Node.js

* NB: Python 2.7 and Java 8 test runners are not yet complete, but both languages are installed in the images so can be manually tested

Prerequisites

You'll need Docker installed

Example

You can run your Lambdas from local directories using the -v arg with docker run – logging goes to stderr and the callback result goes to stdout:

# Test an index.handler function from the current directory on Node.js v4.3
docker run -v "$PWD":/var/task lambci/lambda

# If using a function other than index.handler, with a custom event
docker run -v "$PWD":/var/task lambci/lambda index.myHandler '{"some": "event"}'

# Use the original Node.js v0.10 runtime
docker run -v "$PWD":/var/task lambci/lambda:nodejs

# Run custom commands on the default container
docker run --entrypoint node lambci/lambda -v

# To compile native deps in node_modules (runs `npm rebuild`)
docker run -v "$PWD":/var/task lambci/lambda:build

# Run custom commands on the build container
docker run lambci/lambda:build java -version

# To run an interactive session on the build container
docker run -it lambci/lambda:build bash

Using the Node.js module (npm install docker-lambda) – for example in tests:

var dockerLambda = require('docker-lambda')

// Spawns synchronously, uses current dir – will throw if it fails
var lambdaCallbackResult = dockerLambda({event: {some: 'event'}})

// Manually specify directory and custom args
lambdaCallbackResult = dockerLambda({taskDir: __dirname, dockerArgs: ['-m', '1.5G']})

Create your own Docker image for finer control:

FROM lambci/lambda:build

ENV AWS_DEFAULT_REGION us-east-1

ADD . .

RUN npm install

CMD cat .lambdaignore | xargs zip -9qyr lambda.zip . -x && \
  aws lambda update-function-code --function-name mylambda --zip-file fileb://lambda.zip

# docker build -t mylambda .
# docker run -e AWS_ACCESS_KEY_ID -e AWS_SECRET_ACCESS_KEY mylambda

Questions

• When should I use this?

  When you want fast local reproducibility. When you don't want to spin up an Amazon Linux EC2 instance (indeed, network aside, this is closer to the real Lambda environment because there are a number of different files, permissions and libraries on a default Amazon Linux instance). When you don't want to invoke a live Lambda just to test your Lambda package – you can do it locally from your dev machine or run tests on your CI system (assuming it has Docker support!)

• Wut, how?

  By tarring the full filesystem in Lambda, uploading that to S3, and then piping into Docker to create a new image from scratch – then creating mock modules that will be required/included in place of the actual native modules that communicate with the real Lambda coordinating services. Only the native modules are mocked out – the actual parent JS/PY runner files are left alone, so their behaviors don't need to be replicated (like the overriding of console.log, and custom defined properties like callbackWaitsForEmptyEventLoop)

• What's missing from the images?

  Hard to tell – anything that's not readable – so at least /root/* – but probably a little more than that – hopefully nothing important, after all, it's not readable by Lambda, so how could it be!

• Is it really necessary to replicate exactly to this degree?

  Not for many scenarios – some compiled Linux binaries work out of the box and a CentOS Docker image can compile some binaries that work on Lambda too, for example – but for testing it's great to be able to reliably verify permissions issues, library linking issues, etc.

• What's this got to do with LambCI?

  Technically nothing – it's just been incredibly useful during the building and testing of LambCI.

Documentation

TODO

Docker tags (follow the Lambda runtime names):

• latest / nodejs4.3
• nodejs
• python2.7
• build / build-nodejs4.3
• build-nodejs
• build-python2.7

Env vars:

• AWS_LAMBDA_FUNCTION_NAME
• AWS_LAMBDA_FUNCTION_VERSION
• AWS_LAMBDA_FUNCTION_MEMORY_SIZE
• AWS_LAMBDA_FUNCTION_TIMEOUT
• AWS_LAMBDA_FUNCTION_HANDLER
• AWS_LAMBDA_EVENT_BODY
• AWS_REGION
• AWS_DEFAULT_REGION
• AWS_ACCOUNT_ID
• AWS_ACCESS_KEY_ID
• AWS_SECRET_ACCESS_KEY
• AWS_SESSION_TOKEN

Options to pass to dockerLambda():

• dockerImage
• handler
• event
• taskDir
• cleanUp
• addEnvVars
• dockerArgs
• spawnOptions
• returnSpawnResult

Yum packages installed on build images:

• aws-cli
• zip
• git
• vim
• docker (Docker in Docker!)
• gcc-c++
• clang
• openssl-devel
• cmake
• autoconf
• automake
• libtool