content.md

What is Go?

Go (a.k.a., Golang) is a programming language first developed at Google. It is a statically-typed language with syntax loosely derived from C, but with additional features such as garbage collection, type safety, some dynamic-typing capabilities, additional built-in types (e.g., variable-length arrays and key-value maps), and a large standard library.

wikipedia.org/wiki/Go_(programming_language)

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How to use this image

Note: /go is world-writable to allow flexibility in the user which runs the container (for example, in a container started with --user 1000:1000, running go get github.com/example/... into the default $GOPATH will succeed). While the 777 directory would be insecure on a regular host setup, there are not typically other processes or users inside the container, so this is equivalent to 700 for Docker usage, but allowing for --user flexibility.

Start a Go instance in your app

The most straightforward way to use this image is to use a Go container as both the build and runtime environment. In your Dockerfile, writing something along the lines of the following will compile and run your project (assuming it uses go.mod for dependency management):

FROM %%IMAGE%%:1.20

WORKDIR /usr/src/app

# pre-copy/cache go.mod for pre-downloading dependencies and only redownloading them in subsequent builds if they change
COPY go.mod go.sum ./
RUN go mod download && go mod verify

COPY . .
RUN go build -v -o /usr/local/bin/app ./...

CMD ["app"]

You can then build and run the Docker image:

$ docker build -t my-golang-app .
$ docker run -it --rm --name my-running-app my-golang-app

Compile your app inside the Docker container

There may be occasions where it is not appropriate to run your app inside a container. To compile, but not run your app inside the Docker instance, you can write something like:

$ docker run --rm -v "$PWD":/usr/src/myapp -w /usr/src/myapp %%IMAGE%%:1.20 go build -v

This will add your current directory as a volume to the container, set the working directory to the volume, and run the command go build which will tell go to compile the project in the working directory and output the executable to myapp. Alternatively, if you have a Makefile, you can run the make command inside your container.

$ docker run --rm -v "$PWD":/usr/src/myapp -w /usr/src/myapp %%IMAGE%%:1.20 make

Cross-compile your app inside the Docker container

If you need to compile your application for a platform other than linux/amd64 (such as windows/386):

$ docker run --rm -v "$PWD":/usr/src/myapp -w /usr/src/myapp -e GOOS=windows -e GOARCH=386 %%IMAGE%%:1.20 go build -v

Alternatively, you can build for multiple platforms at once:

$ docker run --rm -it -v "$PWD":/usr/src/myapp -w /usr/src/myapp %%IMAGE%%:1.20 bash
$ for GOOS in darwin linux; do
>   for GOARCH in 386 amd64; do
>     export GOOS GOARCH
>     go build -v -o myapp-$GOOS-$GOARCH
>   done
> done