Amazon Linux Support

[Jinkxed]

Trying to test out docker-slim on amazonlinux base image and it's causes some very weird behavior. All binaries seem to be missing to start so can't even do ls

Example:
Dockerfile
FROM amazonlinux:latest
docker-slim build amazonlinux:latest

[kcq]

Do you have an application container image where you use the Amazon Linux as its base or are you trying to minify the base image itself?

[Jinkxed]

Tried both and got the same results.

Sorry to be more explicit. I build an application container off the amazonlinux:latest container. I've tried running docker-slim on both the base and the application image and it seems to be broke on both.

When I say broke I basically mean there are no files / bin / all the application code or scripts are removed etc.

Easy way to reproduce is by running the above and just typing ls.

[kcq]

What kind of application did you have? Was it a python/ruby/node/java/something else app? What kind of ENTRYPOINT and/or CMD instructions did you have in your Dockerfile? Did you have a wrapper shell script that started your application and potentially did other things or did you invoke your application directly in ENTRYPOINT/CMD or did you have something like supervisord managing several processes in your container or maybe you used docker-compose where you configured the command parameters for your container?

[Jinkxed]

Sorry didn't see this.

None of my applications use entrypoints only commands - most are rails apps. So just running bundle exec rails -s, but this issue happens on the official Amazon Linux image. So even without my customizations it seems to fail on just the base OS image.

[kcq]

@sc-chad thank you for the additional info! really appreciate it!

The base OS image is not a great container to minify because there's no way to know what you need there and what you don't in a significant way. You can leverage the --include-path, --include-shell, --include-exe and --include-bin parameters to tell docker-slim what you want to keep in your base image, but it requires a bit of extra work from you because you need to explicitly specify/decide what you want to keep.

Here's one of the sample apps docker-slim that might be interesting for you (I'd love to add more Rails examples, so if you have any good open source references i'd love to add them): https://github.com/docker-slim/examples/tree/master/ruby_rails_standard

A couple of things to note:

For Rails and Ruby apps in general docker-slim needs the --http-probe parameter when you are minifying the image: docker-slim build --http-probe my/ruby-rails-app (https://github.com/docker-slim/examples/blob/master/ruby_rails_standard/slim.command).

This is necessary to make sure that your Rails app loads extra dependencies it needs, which happens when you its handling HTTP requests.

docker-slim also needs to know about the port(s) your application is using. Normally your Dockerfile would have one or many EXPOSE instructions and docker-slim will see it leveraging it when it's running its HTTP probes (https://github.com/docker-slim/examples/blob/master/ruby_rails_standard/Dockerfile). If your Dockerfile doesn't have any EXPOSE instructions you need to tell docker-slim about your ports similar to how you need to tell docker about the ports you want to use when you execute the run command. With docker-slim it means using the --expose parameter: docker-slim build --http-probe --expose=5000 my/ruby-rails-app

If you are interested I'll be happy to do an online session to walk through your container setup, so we can get your app container minified. You'll get a small container and I'll have an opportunity to make docker-slim easier to use, so everybody wins :-) And if you have containerized Rails examples I'd love to add them to the examples repo.