How can I persist go 1.11 modules in a Docker container?

Question

I am migrating a Go 1.10 app to Go 1.11. This also includes migrating from dep to mod for managing dependencies.

As the application depends on a database, I am using a docker-compose to set up the local development environment. With Go 1.10 I simply mounted the local repository (including the vendor folder) into the correct location in the container's GOPATH:

web:
  image: golang:1.10
  working_dir: /go/src/github.com/me/my-project
  volumes:
    - .:/go/src/github.com/me/my-project
  environment:
    - GOPATH=/go
    - PORT=9999
  command: go run cmd/my-project/main.go

Since Go 1.11 ditches GOPATH (when using modules that is) I thought I could just do the following:

web:
  image: golang:1.11rc2
  working_dir: /app
  volumes:
    - .:/app
  environment:
    - PORT=9999
  command: go run cmd/my-project/main.go

This works, but every time I docker-compose up (or any other command that calls through to the Go tool) it will resolve and re-download the dependency tree from scratch. This does not happen (rather only once) when I run the command outside of the container (i.e. on my local OS).

How can I improve the setup so that the Docker container persists the modules being downloaded by the go tool?

you can always perform the go build up on host then just supply the binary to your container ... in my case the compile happens inside a different container — Scott Stensland, Sep 25 '18 at 00:11
Note that you are using go1.11rc2, which is a release candidate, not the final go1.11 release. — dolmen, Nov 16 '18 at 15:36

score 6 · Accepted Answer · answered Aug 26 '18 at 15:12

6

This is not mentioned in the wiki article on modules, but from reading the updated docs on the go tool, I found out that when using Go modules, the go tool will still use GOPATH to store the available sources, namely $GOPATH/pkg/mod.

This means that for my local dev setup, I can 1. define the GOPATH in the container and 2. mount the local $GOPATH/pkg/mod into the container's GOPATH.

web:
  image: golang:1.11rc2
  working_dir: /app
  volumes:
    - .:/app
    - $GOPATH/pkg/mod:/go/pkg/mod
  environment:
    - GOPATH=/go
    - PORT=9999
  command: go run cmd/my-project/main.go

answered Aug 26 '18 at 15:12

m90

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You also can create a new volume to keep an isolate gopath inside the docker container – Motakjuq Sep 24 '18 at 04:47
@Motakjuq How would that look like in the docker-compose file? – m90 Sep 24 '18 at 08:17

score 5 · Answer 2 · answered Sep 24 '18 at 17:34

You can use a volume instead of your local GOPATH. the docker-compose.yml is like:

version: '3'

services:
  web:
    image: golang:1.11
    working_dir: /app
    volumes:
        - .:/app
        - cache:/go
    environment:
        - PORT=9999
    command: go run cmd/my-project/main.go

volumes:
  cache:

The volume cache is going to persist all the changes on the GOPATH for the container.

How can I persist go 1.11 modules in a Docker container?

2 Answers2

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