AWS Lambda: Docker container support

4 min readJan 3, 2021

One of the most outstanding features brought by AWS for lambda is an AWS Lambda — Container Image Support

Why is that?

Simply because it allows migrating a lot of applications to AWS Lambda.
Before this, packaging dependencies and programming language support was quite a pain for developers new to serverless. On top, running these apps outside the Lambda was hardly possible without some heavy lifting

So, can we use any docker image inside our Lambda workloads?

No, for now, there is still some work that needs to be done to prep those

This is because Lambda functions are being started and invoked in a very specific way, so all these docker images/containers need a special element called Lambda Runtime API in order to work

Multiple approaches to get started with docker container for Lambda :

use base docker images provided by AWS and add your dependencies
make your custom base image and add Lambda Runtime Interface Clients

Summary of constraints :

Docker Registry: only ECR (Elastic Container Registry)
Other registries like DockerHub, GCR, ACR and etc are not yet supported at this time.
Container images size - 10 GB
(Well…more than enough for most modern apps)
Mandatory to use base images with built-in Lambda Runtime API or own customized docker images implementing Lambda Runtime Interface Clients

How to build a docker image for Lambda and use it in a function:

Here is the git repo with sample code

app.js — lambda handler code with simple Hello world response
Dockerfile with build steps for NodeJS using AWS provide a base image
package.json — sample file (no dependencies)

Building NodeJS Docker image for AWS Lambda :

Clone the repo and build the docker image :

git clone https://github.com/advissor/aws-lambda-container-support.git

cd aws-lambda-container-support

docker build -t aws-container-nodejs-hello .

Verify that code works :

Run a container with the image you build in the previous step

docker run -p 9000:8080 aws-container-nodejs-hello

Run a test curl request :

curl -XPOST “http://localhost:9000/2015-03-31/functions/function/invocations" -d ‘{}’

You should receive a JSON response back with Hello World text inside the body

Tagging and pushing docker image to ECR

Creating ECR repo :

aws ecr create-repository — repository-name aws-container-nodejs-hello — image-scanning-configuration scanOnPush=true

Re-tag local image with ECR repo name

docker tag aws-container — nodejs-hello:latest <aws_account_id>.dkr.ecr.<region>.amazonaws.com/aws-container-nodejs-hello:latest

Login to ECR

aws ecr get-login-password | docker login — username AWS — password-stdin <aws_account_id>.dkr.ecr.<region>.amazonaws.com

Push image to ECR

docker push <aws_account_id>.dkr.ecr.<region>.amazonaws.com/aws-container-nodejs-hello:latest

After the image is in ECR we can select it during Lamda function creation

Creating a Lambda function

Selecting container Image

Testing via Sample event
Click on the button next to Actions > Configure test events

Adding a dummy test event :
- create a new test event
- type event name & leave dummy JSON (we are not using any parameters from this JSON, we are using this event to invoke a function manually for verification purposes. Kind of a simulation )
- Click on Create