I'm trying to speed up Docker builds of my Go app. Right now, it's spending maybe 60s just building dependencies (it's a k8s controller, so there are a lot).
One very important constraint: my project depends on private GitHub repos. I do go mod vendor
outside docker build
, where I have creds for the repos set up.
My Dockerfile right now is roughly:
FROM golang:1.12
WORKDIR /src
COPY . .
RUN go build -mod=vendor
...
Even without having to download the deps, that build takes a while because it rebuilds several hundred packages every docker build
.
What I'd like to do is something like:
FROM golang:1.12
WORKDIR /src
# these shouldn't change very often
COPY go.mod go.sum vendor ./
RUN go build -mod=vendor <all dependency packages>
COPY . .
RUN go build -mod=vendor
...
I tried parsing go.mod
, but of course that lists modules, not packages. I tried go list
but never managed to get a working incantation.
I've got a nasty hack that seems to work:
FROM golang:1.12
WORKDIR /src
COPY go.mod go.sum ./
COPY vendor/ ./vendor
RUN go build -mod=vendor $(cat deps|grep -v mypackage | grep -v internal)
COPY . .
RUN go build -mod=vendor
...
go list -f '{{join .Deps "\n"}}' > deps
docker build .
Docker documentation has a guide specific to Go docker images ( Build your Go image ).
It works as follows:
# Layer for dependency installation
COPY go.mod go.sum ./
RUN go mod download
# Layer for app build
COPY . .
RUN go build -o main .
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