golangのアプリをdockerマルチステージビルドで小さいイメージサイズにするメモ

FROM golang:latest as build
ADD ./ ./
ENV GOOS=linux GOARCH=amd64
RUN go build -tags netgo main.go

FROM alpine:latest
COPY --from=build /go/main /app/main
EXPOSE 8080
CMD [ "/app/main" ]

package main

import (
    "fmt"
    "net/http"
)
func index(w http.ResponseWriter, r *http.Request) {
    fmt.Fprintf(w, "golang test")
}

func main() {
    http.HandleFunc("/", index)
    http.ListenAndServe(":8080", nil)
}

% docker build -t gotest test/

% docker images
REPOSITORY   TAG       IMAGE ID       CREATED         SIZE
gotest       latest    83fe32afaf4f   5 minutes ago   11.5MB
alpine       latest    b0e47758dc53   40 hours ago    5.33MB
golang       latest    245bf9f4c37a   13 days ago     728MB

% docker run --name go_docker -d -p 80:8080 gotest
...

% docker ps
CONTAINER ID   IMAGE     COMMAND       CREATED         STATUS         PORTS                               NAMES
eecc22a60f82   gotest    "/app/main"   9 minutes ago   Up 9 minutes   0.0.0.0:80->8080/tcp, :::80->8080/tcp   go_docker

% curl -i -6 http://localhost/
HTTP/1.1 200 OK
Date: Thu, 17 Jun 2021 13:39:51 GMT
Content-Length: 11
Content-Type: text/plain; charset=utf-8

golang test