Multi-platform builds

Intermediate Docker

Mike Metzger

Data Engineering Consultant

Multi-platform?

What does multi-platform mean?
- Different OS types
  - linux
  - windows
  - macos
- Different CPU types
  - x64_64 or amd64
  - arm64
  - arm7
Usually referred to as os/cpu, such as linux/amd64

Linux Tux logo

AMD64 logo

ARM logo

Creating multi-platform builds

Is built on multi-stage build behavior
The initial / build stage tends to use cross-compilers and relies on the architecture of the host system
Final stage uses the architecture / OS for the intended target.

Multi-platform Dockerfile options

Build stage uses the --platform=$BUILDPLATFORM flag
- $BUILDPLATFORM represents the platform of the host running the build
Sometimes uses the ARG directive
- Passes local environment variables into the Docker build system
- In this case, TARGETOS and TARGETARCH
- ARG TARGETOS TARGETARCH
- The environment variables at the host level can be defined previously or using the env command.

Multi-platform example

# Initial stage, using local platform
FROM --platform=$BUILDPLATFORM golang:1.21 AS build

# Copy source into place
WORKDIR /src
COPY . .

# Pull the environment variables from the host
ARG TARGETOS TARGETARCH

# Compile code using the ARG variables
RUN env GOOS=$TARGETOS GOARCH=$TARGETARCH go build -o /final/app .


# Create container and load the cross-compiled code
FROM alpine
COPY --from=build /final/app /bin

Building a multi-platform build

To create a multi-platform build, instead of using docker build, we must use docker buildx with assorted options
docker buildx provides more commands and capabilities over docker build, including the option to specify a platform

docker buildx build --platform linux/amd64,linux/arm64 -t multi-platform-app .

Prior to running the build, we must also have a new builder container present. This is done with the docker buildx create --bootstrap --use command.

Let's practice!

Intermediate Docker