部署的docker image总是太大，怎么办？

sudo docker images

REPOSITORY TAG IMAGE ID CREATED SIZE

docker.io/golang 1.10 d0e7a411e3da 5 days ago 794 MB

docker.io/alpine latest 11cd0b38bc3c 2 weeks ago 4.41 MB

docker 官方golang镜像动不动就几百MB，所以我们只能下载一些优化image 比如apline，相比官方的镜像，小了一半，有些甚至只有几MB大小。

但是会有bug如下：Get https://google.com: x509: failed to load system roots and no roots provided

解决方案就是要添加这个语句在编译文件里面

RUN apk --no-cache add ca-certificates

如果你docker版本是17.05+ 支持多重编译的新特性就可以使用下面的例子，如果不是，就要自己分步执行，操作了。

FROM golang:1.7.3 as builder
WORKDIR /go/src/github.com/alexellis/href-counter/
RUN go get -d -v golang.org/x/net/html 
COPY app.go    .
RUN CGO_ENABLED=0 GOOS=linux go build -a -installsuffix cgo -o app .
 
FROM alpine:latest 
RUN apk --no-cache add ca-certificates
WORKDIR /root/
COPY --from=builder /go/src/github.com/alexellis/href-counter/app .
CMD ["./app"] 

最终编译出来的大小

sudo docker images

REPOSITORY TAG IMAGE ID CREATED SIZE

app_in_apline latest 0cb99ea67ced 2 minutes ago 11.1 MB

但是有一个问题就是上述的开发，编译环境不一致，不如使用同一个库里面开发生产镜像

FROM golang:alpine as build

RUN apk --no-cache add git

ADD . /go/src/github.com/Example/pls3
WORKDIR /go/src/github.com/Example/pls3/cmd/pls3
RUN go get && go install -v

FROM alpine:latest

WORKDIR /
COPY --from=build /go/bin/pls3 /pls3
RUN apk --no-cache add ca-certificates && update-ca-certificates

ARG COMMIT
ENV COMMIT ${COMMIT}

ENTRYPOINT ["/pls3"]

总结，如果编译开发image比较大，生产运行的image比较小，所以在开发镜像开发编译可执行文件，编译的时候加上参数build -a，合入所有依赖到执行文件里面，生产镜像布署，但是一个问题就是生产镜像少东西，还得配置。如果为不配置，而选择完备的镜像，大小又是几百MB，又太大。

ps：删除多余的镜像语句

for i in $(sudo docker images | gawk '{if (NR>1){print $3}}' | head -n 4) ;do sudo docker rmi $i -f ; done;

配置container里面的APP可以访问localhost

I doing a hack similar to above posts of get the local IP to map to a alias name (DNS) in the container. The major problem is to get dynamically with a simple script that works both in Linux and OSX the host IP address. I did this script that works in both environments (even in Linux distribution with "$LANG" != "en_*" configured):

ifconfig | grep -E "([0-9]{1,3}.){3}[0-9]{1,3}" | grep -v 127.0.0.1 | awk '{ print $2 }' | cut -f2 -d: | head -n1

So, using Docker Compose, the full configuration will be:

Startup script (docker-run.sh):

export DOCKERHOST=$(ifconfig | grep -E "([0-9]{1,3}.){3}[0-9]{1,3}" | grep -v 127.0.0.1 | awk '{ print $2 }' | cut -f2 -d: | head -n1)
docker-compose -f docker-compose.yml up

docker-compose.yml:

myapp:
  build: .
  ports:
    - "80:80"
  extra_hosts:
    - "dockerhost:$DOCKERHOST"

Then change http://localhost to http://dockerhost in your code.

For a more advance guide of how to customize the DOCKERHOST script, take a look at this post with a explanation of how it works.