Building Minimize Golang Executable Docker Image with Alpine Linux

Introduction

Building a minimize golang docker image to save image upload time and repository space.

The final image is only about 10 MB.

Step by Step

Docker version above 17.05

1. Use multi-stage builds, Notice:

   • naming stage on FROM by as
   • copy stage file by COPY --from

   # Start from Alpine Linux image with the latest version of Golang
   # Naming build stage as builder
   FROM golang:alpine as builder
   
   # Install Git for go get
   RUN set -eux; \
       apk add --no-cache --virtual git
   
   # Set ENV
   ENV GOPATH /go/
   ENV GO_WORKDIR $GOPATH/src/github.com/dinos80152/golang-docker-alpine/
   
   # Set WORKDIR to go source code directory
   WORKDIR $GO_WORKDIR
   
   # Add files to image
   ADD . $GO_WORKDIR
   
   # Fetch Golang Dependency and Build Binary
   RUN go get
   RUN go install
   
   
   # Start from a raw Alpine Linux image
   FROM alpine:latest
   
   # Install ca-certificates for ssl
   RUN set -eux; \
       apk add --no-cache --virtual ca-certificates
   
   # Copy binary from builder stage into image
   COPY --from=builder /go/bin/golang-docker-alpine .
   
   # Execute binary when docker container starts
   CMD /golang-docker-alpine
   
   # Expose port 8080 to be connected from outside
   EXPOSE 8080
   

2. Build image

   docker build -t golang-docker-alpine .
   

3. Test

   docker run -p 80:8080 -d golang-docker-alpine
   

Docker version lower than 17.05

1. Write Dockerfile for compiling source code to binary on alpine linux

   • DockerfileSrc

   # Start from an Alpine image with the latest version of Go installed
   FROM golang:alpine
   
   # Install Git for go get
   RUN set -eux; \
       apk add --no-cache --virtual git
   
   # Set ENV
   ENV GOPATH /go/
   ENV GO_WORKDIR $GOPATH/src/github.com/dinos80152/golang-docker-alpine/
   
   # Set WORKDIR to go source code directory
   WORKDIR $GO_WORKDIR
   
   # Add files to image
   ADD . $GO_WORKDIR
   
   # Fetch Golang Dependency and Build Binary
   RUN go get
   RUN go install
   

2. Build image from DockerfileSrc

   # build app binary on Alpine OS with golang package
   docker build -t dinos80152/golang-docker-alpine-src -f DockerfileSrc .
   

3. Copy binary from container to host

   # Copy app binary from container to host
   docker cp $(docker create dinos80152/golang-docker-alpine-src):/go/bin/golang-docker-alpine ./
   

4. Write Dockerfile for building image include app binary and pure alpine linux

   • DockerfileBin

   # Start from a raw Alpine image
   FROM alpine:latest
   
   # Install ca-certificates for ssl
   RUN set -eux; \
       apk add --no-cache --virtual ca-certificates
   
   # Copy binary into image
   ADD golang-docker-alpine /
   
   # Execute binary when docker container starts
   CMD /golang-docker-alpine
   
   # Expose port 8080 to be connected from outside
   EXPOSE 8080
   

5. Build docker image from DockerfileBin

   # Build docker image with pure alpine os and app binary
   docker build -t golang-docker-alpine -f DockerfileBin .
   

6. Test

   docker run -p 80:8080 -d golang-docker-alpine
   

Warning

Function time.LoadLocation() will panic in binary image, because of

LoadLocation looks in the directory or uncompressed zip file named by the ZONEINFO environment variable, if any, then looks in known installation locations on Unix systems, and finally looks in $GOROOT/lib/time/zoneinfo.zip.

You have to set $GOROOT and copy zoneinfo.zip manually.

Template

Github Repo online demo with Travis CI and Heroku

Reference

• Alpine Linux
• Use multi-stage builds@docker docs
• Docker golang:alpine
• Docker - how can I copy a file from an image to a host?
• Docker CLI@docker docs
• Dockerfile reference@docker docs
• x509: failed to load system roots and no roots provided