Speeding up Go builds with go 1.10 build cache in Docker containers

Question

I have a Go project with a large vendor/ directory which almost never changes.

I am trying to use the new go 1.10 build cache feature to speed up my builds in Docker engine locally.

Avoiding recompilation of my vendor/ directory would be enough optimization. So I'm trying to do Go equivalent of this common Dockerfile pattern for Python:

FROM python
COPY requirements.txt .              # <-- copy your dependency list
RUN pip install -r requirements.txt  # <-- install dependencies
COPY ./src ...                       # <-- your actual code (everything above is cached)

Similarly I tried:

FROM golang:1.10-alpine
COPY ./vendor ./src/myproject/vendor
RUN go build -v myproject/vendor/... # <-- pre-build & cache "vendor/"
COPY . ./src/myproject

However this is giving "cannot find package" error (likely because you cannot build stuff in vendor/ directly normally either).

Has anyone been able to figure this out?

Answer 1

As of Go 1.11, you would use go modules to accomplish this;

FROM golang
WORKDIR /src/myproject
COPY go.mod go.sum ./             # <-- copy your dependency list
RUN go mod download               # <-- install dependencies
COPY . .                          # <-- your actual code (everything above is cached)

As long as go.sum doesn't change, the image layer created by go mod download shall be reused from cache.