Docker and Go modules
As you may know Go 1.11 includes opt-in feature for versioned modules. Before go modules Gophers used dependency managers like
glide, but with go modules you don’t need a 3rd-party manager as they are included into standard
Also modules allow for the deprecation of the GOPATH, which was a blocker for some newcomers in Go.
In this video I am going to demonstrate how to enable go modules for your program and then package it with Docker. And you will see how easy it is.
Create a project
Let’s create simple http server which will use logrus package for logging.
As I said before go modules is an opt-in feature, which can be enabled by setting environment variable
2 new files have been created in our folder: go.mod and go.sum.
Now if we run
go build it will download deoendencies and build a binary:
go build ./httpserver
Package with Docker
Let’s create a simple Dockerfile for our server.
docker build -t httpserver . docker run -p 8080:8080 httpserver
Cache go modules
As you can see
go build downloads our dependencies. But what is not good here is that it will do it every time we build an image. And imagine if your project have a lot of dependencies, it will slow down your build process. Let’s change something in main.go file and run build again.
To fix this we can use
go mod download which will download dependencies first. But we should re-run it if our go.mod / go.sum files have been changed.
We can do it by copying go.mod / go.sum files into docker first, then run
go mod download, then copy all other files and run
One more thing I like to do with my Dockerfiles is to use multi-stage build to reduce the size of final image. To run our server we only need a binary file, we don’t need the go installed, so inside one Dockerfile we can build program first using
golang image, and then copy only a binary from it to scratch.
So I think go modules is a nice feature, and you definitely should try it, I use it in all my services I write. Of course it needs some improvements, but it works well in practice.