Dockerization of a Golang application

There are several possibilities how to write a Dockerfile for a Golang application. Which one to choose depends on dependencies the application needs.

If the application uses just built in packages, it is possible to have a very minimalistic Dockerfile.


             FROM scratch

             COPY ./goaws /

             CMD ["/goaws"]


Using scratch means we are not basing our image on anything, there is no operating system. This is possible if we do not need to perform any shell operations that require coperation of the OS like mkdir etc.

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If there are non built in dependencies, there there are several approaches possible.

a) The first approach bases the new Docker image on an official golang one, downloads all the dependencies, builds the Go binary and starts the application.

There are several gotchas to watch out for:

The application dependencies, whether internal (packages provided within the application) or external (3rd party packages from the Go public repository) need to be in the right place for the build to be able to find them. The paths searched depend on $GOPATH and $GOROOT environment variables. In the golang:1.8 image OS, the $GOPATH is /go. I created a /go/src/github.com/tamarakaufler/goaws directory which allows the Go compiler to find all internal packages during the build. The go get command will install the external packages and we are good to go (excuse the pun).


             FROM golang:1.8

             RUN mkdir -p /go/src/github.com/tamarakaufler/goaws

             COPY . /go/src/github.com/tamarakaufler/goaws/

             RUN go get github.com/ghodss/yaml

             RUN go get github.com/gorilla/mux

             WORKDIR /go/src/github.com/tamarakaufler/goaws

             RUN go build .

             CMD ["./goaws"]

b) Another option is to create an intermediate image based on an official golang one, install various 3rd party packages that your applications need and copy over internal packages. Then:              FROM my_golang              COPY ./goaws /              CMD ["/goaws"]

where my_golang's Dockerfile is:            FROM golang:1.8            RUN mkdir -p /go/src/github.com/tamarakaufler/goaws            COPY ./app/conf/config.go /go/src/github.com/tamarakaufler/goaws/app/conf/            COPY ./app/router/router.go /go/src/github.com/tamarakaufler/goaws/app/router/            RUN go get github.com/ghodss/yaml            RUN go get github.com/gorilla/mux