Each time I start a new Go project, I repeat many steps. Like set up
.gitignore, CI configs, Dockerfile, ...
So I decide to have a baseline Dockerfile like this:
FROM golang:1.20-bullseye as builder
RUN go install golang.org/dl/go1.20@latest \
&& go1.20 download
WORKDIR /build
COPY go.mod .
COPY go.sum .
COPY vendor .
COPY . .
RUN CGO_ENABLED=0 GOOS=linux GOARCH=amd64 GOAMD64=v3 go build -o ./app -tags timetzdata -trimpath -ldflags="-s -w" .
FROM gcr.io/distroless/base-debian11
COPY --from=builder /build/app /app
ENTRYPOINT ["/app"]
I use multi-stage build to keep my image size small. First stage is Go official image, second stage is Distroless.
Before Distroless, I use Alpine official image, There is a whole discussion on the Internet to choose which is the best base image for Go. After reading some blogs, I discover Distroless as a small and secure base image. So I stick with it for a while.
Also, remember to match Distroless Debian version with Go official image Debian version.
FROM golang:1.20-bullseye as builder
This is Go image I use as a build stage. This can be official Go image or custom image is required in some companies.
RUN go install golang.org/dl/go1.20@latest \
&& go1.20 download
This is optional. In my case, my company is slow to update Go image so I use this trick to install latest Go version.
WORKDIR /build
COPY go.mod .
COPY go.sum .
COPY vendor .
COPY . .
I use /build to emphasize that I am building something in
that directory.
The 4 COPY lines are familiar if you use Go enough. First is
go.mod and go.sum because it defines Go modules.
The second is vendor, this is optional but I use it because I
don't want each time I build Dockerfile, I need to redownload Go modules.
RUN CGO_ENABLED=0 GOOS=linux GOARCH=amd64 GOAMD64=v3 go build -o ./app -tags timetzdata -trimpath -ldflags="-s -w" .
This is where I build Go program.
CGO_ENABLED=0 because I don't want to mess with C
libraries.
GOOS=linux GOARCH=amd64 is easy to explain, Linux with
x86-64.
GOAMD64=v3 is new since
Go 1.18, I
use v3 because I read about AMD64 version in
Arch Linux rfcs. TLDR's newer computers are already x86-64-v3.
-tags timetzdata to embed timezone database in case base
image does not have.
-trimpath to support reproduce build.-ldflags="-s -w" to strip debugging information.FROM gcr.io/distroless/base-debian11
COPY --from=builder /build/app /app
ENTRYPOINT ["/app"]
Finally, I copy app to Distroless base image.