CODEWITHSUNDEEP
dockergodockerfilego-modules
nfirvine
nfirvine

Reputation: 1539

Build go dependencies in separate Docker layer

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.

Upvotes: 7

Views: 2071

Answers (2)

Tom&#225;š Drozd&#237;k
Tom&#225;š Drozd&#237;k

Reputation: 1

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 .

Upvotes: 0

nfirvine
nfirvine

Reputation: 1539

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 .

Upvotes: 2

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