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Building and Testing Docker Images

Dockerfiles and scripts for starting and managing our containers are located in the docker/ directory.

Local Development

Use docker compose up, which will use the docker/start.sh script to run Yarn scripts.

Testing Container Builds

Build a container image:

# <service> should be one of ('api', 'game', 'sp', 'worker')
# <version> should match the latest git release; defaults to 'testing'
scripts/build_container.sh <service> <version>

Test a container image:

# This should successfully start the SP server.
# Ctrl-C should successfully terminate the container.
docker run -it duelyst-sp

Publishing Containers to ECR

Tag and publish a container image:

# <service> should be one of ('api', 'game', 'sp', 'worker')
# <version> should match the latest git release
# <registry> is your AWS ECR registry alias
# <repo> is your AWS ECR repository name
scripts/publish_container.sh <service> <version> <registry> <repo>

Notes on Image Sizes

There are a few strategies we use to keep image sizes small:

  1. Use an alternative base image, i.e. node:18-slim instead of node:18
  2. Avoid installing Node.js devDependencies in container builds
  3. Purge the Yarn cache from container builds

Comparison of Base Images

Sizes of Docker images built by scripts/build_container.sh:

Service Image Size ECR Size 50 GB Limit
Node.js node:18 942 MB N/A N/A
Node.js node:18-slim 234 MB N/A N/A
Node.js node:18-alpine 165 MB N/A N/A
Node.js node:16 858 MB N/A N/A
Node.js node:16-slim 174 MB N/A N/A
Node.js node:16-alpine 114 MB N/A N/A
API node:18 1170 MB 425 MB 117 / 23 ea
API node:18-slim 767 MB 254 MB 196 / 39 ea
API node:18-alpine 626 MB 187 MB 267 / 53 ea
API node:16 1040 MB 396 MB 126 / 25 ea
API node:16-slim 615 MB 214 MB 233 / 46 ea
API node:16-alpine 530 MB 169 MB 295 / 59 ea

Image sizes reported by docker image ls include all layers, and are much higher than the image sizes reported by ECR. ECR gives us 50 GB of storage for free, so the 50 GB Limit column shows how many total images we can store for each image, and how many we can store for each of the five services we build.

The -alpine images pull Node.js builds from unofficial-builds.nodejs.org, while the default and -slim images pull official builds from nodejs.org. While the -slim images are 25-35% larger than the -alpine images, they're still small enough to allow us to store several dozen versions in ECR before we start to approach the 50 GB ECR limit. Additionally, the -slim images are based on Debian, which comes with a more familiar toolchain.

Similarly, Node.js v18 images are 10-20% larger than Node.js v16 images, but we may be able to get some of this size back by replacing Mocha, Axios, and other dependencies with their new native counterparts in Node.js v18.

Regarding bcrypt

We could further reduce image sizes by removing the bcrypt dependencies from the base image layer. These currently include python3, make, gcc, and g++. The bcrypt dependency is only used by the API service, during the login flow in server/routes/session.coffee. One option here could be to move authentication flows (such as JWT signing, granting, and validation) to their own microservice to isolate this dependency, reducing the image size of all other services.