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Last pushed: 2 years ago
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This is the smallest Swift language image that I know how to make.
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This is the smallest Swift Docker image that I know how to make. I use this image as a production base for Swift language projects.


The "supported" Swift configuration is Ubuntu. However, I run Debian, and prefer more minimal Docker images in general. So, I set out to create a "proper" minimal Debian image.


Just pull from drewcrawford/swift. It's installed to /usr/local.

Then you can compile swift programs, for example,

$ docker run -it drewcrawford/swift:latest
# echo 'print("hello world")' > test.swift
# swiftc tests.swift
# exit
$ docker cp 4afdd757d428:test .

Now you can build a docker image with only your program:

FROM drewcrawford/swift-runtime:latest
ADD test


You can build the compiler with docker build .. You may want to up the number of cores if you're using VirtualBox, because it takes a long time single-threaded.

After building the swift image, you can build the separate swift-runtime image via

id=$(docker create drewcrawford/swift:latest)
docker cp $id:usr/local/lib/swift - > swiftlibs.tar
docker rm -v $id
docker build -f Runtime.dockerfile .


Here's a riddle: if sourcecode exists on GitHub, and nobody compiles it, is the project open-source?

Answer: We compile it. So I don't know.

The Swift build system is kind of convoluted, and building an installable package is not documented anywhere (that I can find anyway). I guess we'll give clattner a pass for being awesome otherwise, but it is hairy.

I dove into the build system, and worked out what (I think) they do to build a tarball, and here it is! This image should build, run, test, and validate Swift exactly as upstream does. Then we just turn around and install that tarball to /usr/local.

Since we build from source, you could modify this image to apply your own custom patches before building if you like. As such this Dockerfile may be useful as a reference for a workflow for developing Swift itself.


Q: Can't you use Alpine?

A: No.

Q: How large is this image?

A: 664.6 MB, at the time of this writing. 125.1 of that is Debian. We uninstall all the build dependencies, so I don't know how to make it smaller.

Note that the distributable swift-runtime image is only 187.9 MB.

Q: Do I need this image to run Swift binaries?

A: Probably not. You probably only need the (smaller) swift-runtime image for containers that are supposed to contain compiled Swift code.

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