Docker实践之.NET6基于Dockerfile构建Docker镜像

前面都在说Docker镜像，那么Docker镜像是如何构建的呢？今天我们就来学习一下，如何基于Dockerfile来构建Docker镜像。

创建一个.NET6最小API

这里我用VS2022创建一个Docker运行的最小API，

VS会自动帮我们生产Dockerfile文件

我直接把代码上传到宿主机上，

一般我们都是上传到git，然后通过jenkins来调用shell脚本来构建镜像并上传到镜像仓库。

进入到Dockerfile目录，执行构建命令docker build -t 镜像名:版本 .

[root@VM-12-3-centos DockerWeb]# docker build -t docker-web .
Sending build context to Docker daemon  13.82kB
Step 1/17 : FROM mcr.microsoft.com/dotnet/aspnet:6.0 AS base
6.0: Pulling from dotnet/aspnet
a2abf6c4d29d: Already exists
08af7dd3c640: Pull complete
742307799914: Pull complete
a260dbcd03fc: Pull complete
96c3c696f47e: Pull complete
Digest: sha256:7696d5b456eede87434c232b9070f40659ff0c4b71ca622cf197815ccaee661d
Status: Downloaded newer image for mcr.microsoft.com/dotnet/aspnet:6.0
 ---> 8d32e18b77a4
Step 2/17 : WORKDIR /app
 ---> Running in e6c17cf8d13c
Removing intermediate container e6c17cf8d13c
 ---> a572d041e0da
Step 3/17 : EXPOSE 80
 ---> Running in d13e67c50b6d
Removing intermediate container d13e67c50b6d
 ---> bbbbe840e85e
Step 4/17 : EXPOSE 443
 ---> Running in 567ce4adadc9
Removing intermediate container 567ce4adadc9
 ---> dfc3eb0c4065
Step 5/17 : FROM mcr.microsoft.com/dotnet/sdk:6.0 AS build
6.0: Pulling from dotnet/sdk
a2abf6c4d29d: Already exists
08af7dd3c640: Already exists
742307799914: Already exists
a260dbcd03fc: Already exists
96c3c696f47e: Already exists
d81364490ceb: Pull complete
3e56f7c4d95f: Pull complete
9939dbdaf4a7: Pull complete
Digest: sha256:a7af03bdead8976d4e3715452fc985164db56840691941996202cea411953452
Status: Downloaded newer image for mcr.microsoft.com/dotnet/sdk:6.0
 ---> e86d68dca8c7
Step 6/17 : WORKDIR /src
 ---> Running in b3db267dfde3
Removing intermediate container b3db267dfde3
 ---> 1e44b66e7fcc
Step 7/17 : COPY ["DockerWeb.csproj", "."]
 ---> 7af02dfd823e
Step 8/17 : RUN dotnet restore "./DockerWeb.csproj"
 ---> Running in 22c508e5bfb8
  Determining projects to restore...
  Restored /src/DockerWeb.csproj (in 3.04 sec).
Removing intermediate container 22c508e5bfb8
 ---> 530712ad2cb4
Step 9/17 : COPY . .
 ---> 9f72854995f8
Step 10/17 : WORKDIR "/src/."
 ---> Running in 4a4a8225dd93
Removing intermediate container 4a4a8225dd93
 ---> b60fdb650fdc
Step 11/17 : RUN dotnet build "DockerWeb.csproj" -c Release -o /app/build
 ---> Running in a49f8a39451c
Microsoft (R) Build Engine version 17.0.0+c9eb9dd64 for .NET
Copyright (C) Microsoft Corporation. All rights reserved.

  Determining projects to restore...
  All projects are up-to-date for restore.
  DockerWeb -> /app/build/DockerWeb.dll

Build succeeded.
    0 Warning(s)
    0 Error(s)

Time Elapsed 00:00:02.92
Removing intermediate container a49f8a39451c
 ---> 58c5a002da43
Step 12/17 : FROM build AS publish
 ---> 58c5a002da43
Step 13/17 : RUN dotnet publish "DockerWeb.csproj" -c Release -o /app/publish
 ---> Running in b60058485f34
Microsoft (R) Build Engine version 17.0.0+c9eb9dd64 for .NET
Copyright (C) Microsoft Corporation. All rights reserved.

  Determining projects to restore...
  All projects are up-to-date for restore.
  DockerWeb -> /src/bin/Release/net6.0/DockerWeb.dll
  DockerWeb -> /app/publish/
Removing intermediate container b60058485f34
 ---> c5456b5f5ad1
Step 14/17 : FROM base AS final
 ---> dfc3eb0c4065
Step 15/17 : WORKDIR /app
 ---> Running in cf76a79268ee
Removing intermediate container cf76a79268ee
 ---> 6a0b49e53f4a
Step 16/17 : COPY --from=publish /app/publish .
 ---> acf5b1cb9f98
Step 17/17 : ENTRYPOINT ["dotnet", "DockerWeb.dll"]
 ---> Running in da2fa62b807b
Removing intermediate container da2fa62b807b
 ---> bb42b5515f09
Successfully built bb42b5515f09
Successfully tagged docker-web:latest

镜像构建成功后，便可以在镜像中找到我们构建的镜像

[root@VM-12-3-centos DockerWeb]# docker images
REPOSITORY                        TAG       IMAGE ID       CREATED         SIZE
docker-web                        latest    bb42b5515f09   2 minutes ago   212MB

启动镜像

docker run -d --name docker-web  -p 8880:80 docker-web

这里，一个.net6从构建到启动的流程的基操就over了，微软很贴心的为我们生产了Dockerfile，使得我们的操作尤为简便。但是，大多时候需要我们自己去构建Dockerfile,那么，我们就需要去了解一下怎么编写Dockerfile

Dockerfile

我们就基于前面VS帮我们生成的Dockerfile来学习一下如何编写自己的Dockerfile,

FROM mcr.microsoft.com/dotnet/aspnet:6.0 AS base
WORKDIR /app
EXPOSE 80
EXPOSE 443

FROM mcr.microsoft.com/dotnet/sdk:6.0 AS build
WORKDIR /src
COPY ["DockerWeb.csproj", "."]
RUN dotnet restore "./DockerWeb.csproj"
COPY . .
WORKDIR "/src/."
RUN dotnet build "DockerWeb.csproj" -c Release -o /app/build

FROM build AS publish
RUN dotnet publish "DockerWeb.csproj" -c Release -o /app/publish

FROM base AS final
WORKDIR /app
COPY --from=publish /app/publish .
ENTRYPOINT ["dotnet", "DockerWeb.dll"]

其实这个脚本对于入门还是稍微负责了一些，这里涉及到了多阶段构建，先不管，我们先弄清楚里面的一些关键字及作用。

• FROM : 基于哪个镜像，可以前端构建好的阶段别名，AS 给当前层镜像定义一个别名,别名可以在后面的构建阶段中使用
• WORKDIR：类似于cd，如果目录不存在，会自动创建该目录
• EXPOSE：容器要开放的端口，一般是程序启动的端口，
• COPY：拷贝文件，一般是从宿主机目录复制到镜像里的指定目录，当然它还可以再多阶段构建过程中，从前阶段复制到当前阶段，如:COPY –from=publish /app/publish .
• RUN: 执行脚本命令
• ENTRYPOINT：容器启动时的参数，如：ENTRYPOINT [“dotnet”, “DockerWeb.dll”]，当我们启动容器时，便会执行dotnet DockerWeb.dll，如果存在多个ENTRYPOINT命令，只有最后条命令生效。
• CMD：和ENTRYPOINT功能类似，只不过CMD可以在启动时覆盖
• ENV：设置容器环境变量，如:ENV JAVA_OPTS="-server -Xmx2g -Xms2g"
• VOLUME：容器挂载目录，会在容器启动时，自动挂载到宿主机。如果在docker run时指定了-v参数来映射挂载目录则会覆盖默认挂载目录。

这里我们就把前面的Dockerfile改一下，弄一个简单一点的

# 基于 mcr.microsoft.com/dotnet/sdk:6.0镜像
FROM mcr.microsoft.com/dotnet/sdk:6.0
#进入到工作目录
WORKDIR /app
# 复制宿主机当前目录文件至镜像根目录
COPY . .
# 还原.net引用包
RUN dotnet restore 
# 编译发布
RUN dotnet publish -c Release -o /app/publish
# 暴露端口
EXPOSE 80
# 启动运行
ENTRYPOINT ["dotnet", "DockerWeb.dll"]

这里我们新建一个名为Dockerfile-sample的脚本文件，讲上面的构建脚本拷贝进去，然后执行构建命令docker build -f Dockerfile-sample -t docker-web-sample .

 [root@VM-12-3-centos DockerWeb]# docker build -f Dockerfile-sample -t docker-web-sample .
Sending build context to Docker daemon  13.31kB
Step 1/7 : FROM mcr.microsoft.com/dotnet/sdk:6.0
 ---> e86d68dca8c7
Step 2/7 : WORKDIR /app
 ---> Running in 8c8f849824a1
Removing intermediate container 8c8f849824a1
 ---> 6b2f44c516d8
Step 3/7 : COPY . .
 ---> 0e31eac361dd
Step 4/7 : RUN dotnet restore
 ---> Running in a1d2a2f605ec
  Determining projects to restore...
  Restored /app/DockerWeb.csproj (in 3.47 sec).
Removing intermediate container a1d2a2f605ec
 ---> 0218643eef01
Step 5/7 : RUN dotnet publish -c Release -o /app/publish
 ---> Running in 0f59735014d0
Microsoft (R) Build Engine version 17.0.0+c9eb9dd64 for .NET
Copyright (C) Microsoft Corporation. All rights reserved.

  Determining projects to restore...
  All projects are up-to-date for restore.
  DockerWeb -> /app/bin/Release/net6.0/DockerWeb.dll
  DockerWeb -> /app/publish/
Removing intermediate container 0f59735014d0
 ---> 68cbad659576
Step 6/7 : EXPOSE 80
 ---> Running in b9b13621c4ee
Removing intermediate container b9b13621c4ee
 ---> 6fc0b9507a88
Step 7/7 : ENTRYPOINT ["dotnet", "DockerWeb.dll"]
 ---> Running in 569d0b39ec06
Removing intermediate container 569d0b39ec06
 ---> 02f1827b8c43
Successfully built 02f1827b8c43
Successfully tagged docker-web-sample:latest

这次构建并没有通过多阶段构建，那么为什么需要多阶段构建呢？我们来看一下两种构建方式的镜像文件，

可以看到，多阶段构建出来的镜像只有212MB，未进行多阶段构建出来的镜像有764MB,这在镜像推送和拉取时，镜像较小的文件的优势便体现出来了。