- Published on
Build Small Golang Docker Containers
- Authors
- Name
- Ruan Bekker
- @ruanbekker
In this tutorial I will show you how to build really small docker containers for golang applications. And I mean the difference between 310MB down to 2MB
But Alpine..
So we thinking lets go with alpine right? Yeah sure lets build a small, app running on go with alpine.
Our application code:
package main
import (
"fmt"
"math/rand"
"time"
)
func main() {
lekkewords := []string{
"dog", "cat", "fish", "giraffe",
"moo", "spider", "lion", "apple",
"tree", "moon", "snake", "mountain lion",
"trooper", "burger", "nasa", "yes",
}
rand.Seed(time.Now().UnixNano())
var zelength int = len(lekkewords)
var indexnum int = rand.Intn(zelength-1)
word := lekkewords[indexnum]
fmt.Println("Number of words:", zelength)
fmt.Println("Selected index number:", indexnum)
fmt.Println("Selected word is:", word)
}
Our Dockerfile:
FROM golang:alpine
WORKDIR $GOPATH/src/mylekkepackage/mylekkeapp/
COPY app.go .
RUN go build -o /go/app
CMD ["/go/app"]
Let's package our app to an image:
docker build -t mygolangapp:using-alpine .
Inspect the size of our image, as you can see it being 310MB
docker images "mygolangapp:*"
REPOSITORY TAG IMAGE ID CREATED SIZE
mygolangapp using-alpine eea1d7bde218 About a minute ago 310MB
Just make sure it actually works:
docker run mygolangapp:using-alpine
Number of words: 16
Selected index number: 11
Selected word is: mountain lion
But for something just returning random selected text, 310MB is a bit crazy.
Multi Stage Builds
As Go binaries are self-contained, we can make use of docker's multi stage builds, where we can build our application on alpine and use the binary on a scratch image:
Our multi stage Dockerfile:
FROM golang:alpine AS builder
WORKDIR $GOPATH/src/mylekkepackage/mylekkeapp/
COPY app.go .
RUN go build -o /go/app
FROM scratch
COPY /go/app /go/app
CMD ["/go/app"]
Build it:
docker build -t mygolangapp:using-multistage -f Dockerfile.multi .
Notice that the image is only 2.01MB, say w000t!
docker images "mygolangapp:*"
REPOSITORY TAG IMAGE ID CREATED SIZE
mygolangapp using-multistage 31474c61ba5b 15 seconds ago 2.01MB
mygolangapp using-alpine eea1d7bde218 2 minutes ago 310MB
Run the app:
docker run mygolangapp:using-multistage
Number of words: 16
Selected index number: 5
Selected word is: spider
Resources
Source code for this demonstration can be found at github.com/ruanbekker/golang-build-small-images
Thank You
Thanks for reading, if you like my content, feel free to check out my website, and subscribe to my newsletter or follow me at @ruanbekker on Twitter.
- Linktree: https://go.ruan.dev/links
- Patreon: https://go.ruan.dev/patreon