A small Golang webservice Dockerimage

Here is the Dockerfile for a small golang webservice I wrote, which I managed to make quite small. Saving it for myself and I guess I may as well share it since I think it will otherwise be thrown away.

Note I’ve replaced the more project-specific stuff. Like the project name and package. Probably there is some smarter way to compile it with the correct path.

# The file has two steps, first the builder then the actual running image.
# This part identifies it as the builder.
FROM golang:1.10 as builder

# Create appuser to avoid running as root later
RUN adduser --system appuser

# Import the project onto where it would go on the gopath
WORKDIR /go/src/github.com/<username>/<project>
COPY . .

# Fetch dependencies
RUN go get -d -v ./...
# Compile the binary. Mind the flags because it has to work in the next image.
RUN CGO_ENABLED=0 GOOS=linux GOARCH=amd64 go build -a -installsuffix cgo .

# Here we start the actual image. Scratch is super barebones.
FROM scratch

WORKDIR /

# Copy over the files we need.
# The ssl certs are needed for doing any kind of ssl connection
COPY --from=builder /etc/ssl/certs/ca-certificates.crt /etc/ssl/certs/
# The actual binary.
COPY --from=builder /go/src/github.com/<username>/<project>/<project> /<project>
COPY --from=builder /etc/passwd /etc/passwd

# Use the non-root user.
USER appuser

# The tcp port to expose, in my case 1323 which is the default of the framework I use.
EXPOSE 1323

# Start the binary as the entrypoint.
ENTRYPOINT ["/<project>"]

When building this Dockerfile for my project, I get an image that is only 13.1MB big. Pretty good, compared to other services in e.g. NodeJS or Python that I have made before that usually end up 300MB+.

Published Sep 24, 2018