(assets): allow user to pass platform option to Docker builds

Use Case

To be able to build images for amd64 architecture (e.g. AWS Fargate) on a system that is using other architecture like arm64 (e.g. Apple M1).

Proposed Solution

Replace docker build with docker buildx build.

https://docs.docker.com/buildx/working-with-buildx/#build-multi-platform-images

With buildx you can build cross-platform images by declaring --platform argument. e.g. docker buildx build --platform linux/amd64 someimage:sometag . executed on system Apple M1 results in an image which works system with amd64 architecture.

buildx allows you also to build image for multiple platforms at once. e.g. --platform linux/amd64,linux/arm64

Other

Currently image .fromAsset results in an image that works only on the same architecture where it was built. In that sense, this could be considered also a bug – the image built doesn’t work on the target system (Fargate).

import { FargateTaskDefinition, ContainerImage } from '@aws-cdk/aws-ecs';

const taskDefinition = new FargateTaskDefinition(this, 'TaskDefinition');

taskDefinition
  .addContainer('Container', {
    image: ContainerImage.fromAsset(path.resolve(__dirname, '../image')),
  });

• 👋 I may be able to implement this feature request
• ⚠️ This feature might incur a breaking change

---

This is a 🚀 Feature Request

[lmammino]

One solution that I found (after much head banging 🙉 ) is to put --platform ... in the FROM instruction at the beginning of my Dockerfile:

FROM --platform=linux/amd64 someBaseImage:someVersion
# ... moar cool docker stuff here 🐳

You could also use a build arg to specify an arbitrary value for platform or create different target images for different platforms you need to support.

I hope this helps 😃

[arekt]

Just a note for people with M1 chip. Docker supports DOCKER_DEFAULT_PLATFORM=‘linux/amd64’ env variable now. https://docs.docker.com/engine/reference/commandline/cli/