72 lines
3.1 KiB
Markdown
72 lines
3.1 KiB
Markdown
# What is Go?
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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.
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> [wikipedia.org/wiki/Go_(programming_language)](http://en.wikipedia.org/wiki/Go_%28programming_language%29)
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%%LOGO%%
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# How to use this image
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**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 `$GOPATH` will succeed). While the `777` directory would be insecure on a regular host setup, there are not typically other processes or users inside the container, so this is equivalent to `700` for Docker usage, but allowing for `--user` flexibility.
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## Start a Go instance in your app
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The most straightforward way to use this image is to use a Go container as both the build and runtime environment. In your `Dockerfile`, writing something along the lines of the following will compile and run your project (assuming it uses `go.mod` for dependency management):
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```dockerfile
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FROM %%IMAGE%%:1.19
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WORKDIR /usr/src/app
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# pre-copy/cache go.mod for pre-downloading dependencies and only redownloading them in subsequent builds if they change
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COPY go.mod go.sum ./
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RUN go mod download && go mod verify
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COPY . .
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RUN go build -v -o /usr/local/bin/app ./...
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CMD ["app"]
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```
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You can then build and run the Docker image:
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```console
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$ docker build -t my-golang-app .
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$ docker run -it --rm --name my-running-app my-golang-app
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```
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## Compile your app inside the Docker container
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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:
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```console
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$ docker run --rm -v "$PWD":/usr/src/myapp -w /usr/src/myapp %%IMAGE%%:1.19 go build -v
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```
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This will add your current directory as a volume to the container, set the working directory to the volume, and run the command `go build` which will tell go to compile the project in the working directory and output the executable to `myapp`. Alternatively, if you have a `Makefile`, you can run the `make` command inside your container.
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```console
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$ docker run --rm -v "$PWD":/usr/src/myapp -w /usr/src/myapp %%IMAGE%%:1.19 make
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```
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## Cross-compile your app inside the Docker container
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If you need to compile your application for a platform other than `linux/amd64` (such as `windows/386`):
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```console
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$ docker run --rm -v "$PWD":/usr/src/myapp -w /usr/src/myapp -e GOOS=windows -e GOARCH=386 %%IMAGE%%:1.19 go build -v
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```
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Alternatively, you can build for multiple platforms at once:
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```console
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$ docker run --rm -it -v "$PWD":/usr/src/myapp -w /usr/src/myapp %%IMAGE%%:1.19 bash
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$ for GOOS in darwin linux; do
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> for GOARCH in 386 amd64; do
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> export GOOS GOARCH
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> go build -v -o myapp-$GOOS-$GOARCH
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> done
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> done
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```
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