reducing image size

[kaczmarj]

Hi @vsoch - cool project! You might consider using multi-stage builds to reduce the image size. Basically, you install all the compile-time dependencies and build singularity in the first stage, and copy the artifacts and install run-time dependencies in the second stage.

I do this, for example, in this Dockerfile.

This does, however, remove the source code and other potentially useful build artifacts. If those are useful to this project, then I would advise against multi-stage builds.

[vsoch]

Hey @kaczmarj! That's a good suggestion! I would say that reproducibility is important, and a part of that is retaining the source code (and as you mention, other build artifacts.) Is the difference in size truly significant? Either way, thanks for showing me this trick! I think I will definitely give it a try for other projects.

[kaczmarj]

The difference can be large. Building version 3.0.2 in a single stage creates a Docker image that is 732 MB large. With the second stage, the image is 112 MB. A large part of that is that golang and gcc are gone.

Building current 2.x master in a single stage creates a 266 MB image, and with multi-stage creates 57.7 MB image.

So if you would like to use multi-stage builds, you can also copy over the source code and other important things. But to be fully reproducible, you'd probably want to keep the compile-time dependencies (including the compilers!) in there as well.

[vsoch]

Agreed! Thanks for the useful info. If this is important to you and you want to provide a multistage build for users, I'd be happy to add a branch with the tag. Let me know - I can create the branch off of another, and then you can PR to it, and then push to Docker Hub to find under the singularityware namespace. I'm a stickler for reproducibility, but this isn't essential for everyone, and I recognize some users might prefer the smaller image.

[vsoch]

We can call it 3.0.2-slim since that's how they normally roll the smaller version of these things :)

[kaczmarj]

This isn't very important to me :) I mostly wanted to let you know that this is possible. But if you'd like, I can create a 3.0.2-slim PR.

[vsoch]

Yeah, to be honest I just have fun doing the collaboration / Github things, so let's do it! Give me a few minutes and I'll get you a branch ready.

[vsoch]

Okay, we are ready to go (no pun intended)! here is your branch, and it's set up for an automated build on Docker Hub. I've also gone ahead and added a (non slim, very fat) 3.0.2 branch and container for it too.

[vsoch]

The build is queued - I'll keep watch and close this issue when it's ready. Thanks for putting this together!

[vsoch]

https://hub.docker.com/r/singularityware/singularity/tags

[kaczmarj]

Nice and slim :)