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:1.18-bullseye as builder
RUN go install golang.org/dl/go1.18@latest \
&& go1.18 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 .
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:1.18-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/go1.18@latest \
&& go1.18 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 .
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 incase base image does not have.-trimpath to support reproduce build.
FROM gcr.io/distroless/base-debian11
COPY --from=builder /build/app /app
ENTRYPOINT ["/app"]
Finally, I copy app to Distroless base image.