Docker

Docker Multi Stage Build

Docker, Go


Docker 17.05版的發布了Multi-stage build, 讓image肥大的問題有了優雅的解法.

Our Go program :

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package main

import "fmt"

func main() {
	fmt.Println("Hello world!")
}

Single-stage build

Dockerfile :

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FROM golang:alpine
WORKDIR /app
ADD . /app
RUN cd /app && go build -o goapp
ENTRYPOINT ./goapp
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# build image
docker build -t main .
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docker images | grep main



352MB的鏡像大小, 這對於要快速佈署是相當的肥大的.
因為Go只需要編譯完成的binary檔, Go image其實只是輔助編譯source code用的.
所以透過Multi-Stage build 來減少程式的鏡像檔大小.

Multi-Stage Build

適用在需要編譯環境的應用上(GO, C, JAVA…)
至少都會需要兩個環境的Docker image:

  • 編譯環境鏡像
    • 完整的編譯引擎, 依賴庫等等
  • 運行環境鏡像
    • 編譯好的二進制檔, 用來執行app, 因為沒有編譯環境, 所以體機會小上很多
      使用multi-stage build, 可以使用單一的dockerfile, 降低維護複雜度.
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# build stage
FROM golang:alpine AS build-env
ADD . /src
RUN cd /src && go build -o goapp

#final stage
FROM alpine
WORKDIR /app
COPY --from=build-env /src/goapp /app/
ENTRYPOINT ./goapp


7.58MB

More Examples

Import “time”

  • main.go
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    package main

    import (
    	"fmt"
    	"time"
    )

    func main() {

    	location, err := time.LoadLocation("Europe/Berlin")
    	if err != nil {
    		fmt.Println(err)
    	}

    	t := time.Now().In(location)

    	fmt.Println("Time in Berlin:", t.Format("02.01.2006 15:04"))
    }

build 完之後執行會出錯

搜尋該錯誤 panic: time: missing Location in call to Time.In
搜尋Google後得知, 原來時區位置是從本地文件讀取出的.
可以透過安裝tzdata, 在/usr/share/zoneinfo產生各時區的資訊; 或者複製機器上的
修改Dockefile

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# build stage
FROM golang:alpine AS build-env
ADD . /src
WORKDIR /src
RUN go build -o goapp

#final stage
FROM alpine
WORKDIR /app
# RUN apk add --no-cache tzdata
# COPY --from=build-env /etc/ssl/certs/ca-certificates.crt /etc/ssl/certs/
COPY --from=build-env /usr/share/zoneinfo /usr/share/zoneinfo
COPY --from=build-env /src/goapp /app/
ENTRYPOINT ./goapp

Go Module

App Code + go.mod + go.sum

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// main.go
package main

import (
	"github.com/gin-gonic/gin"
)

func main() {
	r := gin.Default()
	r.GET("/ping", func(c *gin.Context) {
		c.JSON(200, gin.H{
			"message": "pong",
		})
	})
	r.Run()
}

1. Build Golang App

準備官方的Golang image, 並且取別名為builder-env, 方便在之後的階段來使用
設定工作目錄,
因為我是用go module作套件依賴管理,
這裡把路徑設定成跟我們開發環境中一樣, 都是GOPATH下(go/src)的路徑.
複製代碼, 並且安裝依賴, 編譯go app

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FROM golang  AS build-env
WORKDIR /go/src/github.com/tedmax100/docker-multistage-build-demo
COPY . .
ENV GO111MODULE=on
RUN CGO_ENABLED=0 GOOS=linux go build -o main

2. Deployment image

使用scratch 來作基礎image
把編譯好的程式放在裡面;
scratch大小 比alpine還小.
如果app 需要SSL/TLS來進行訪問, 則需要複製ca-certificates

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FROM scratch
WORKDIR /bin
# COPY --from=build-env /etc/ssl/certs/ca-certificates.crt /etc/ssl/certs/ca-certificates.crt
COPY --from=build-env /go/src/github.com/tedmax100/mahjong .
CMD ["./main"]

僅產生出15.Mb的image

docker build

透過–rm 刪除中間過程產生的容器

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docker build --rm -t main .

docker run

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docker run --rm -d -p 8081:8080 main

source code

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