构建更小的容器镜像的技巧
容器 Dockerfile
![](/data/attachment/album/201905/22/111342rthd3dh2d0ps4d2d.jpg)


Linux 容器已经成为一个热门话题，保证容器镜像较小被认为是一个好习惯。本文提供了有关如何构建较小 Fedora 容器镜像的一些技巧。


### microdnf


Fedora 的 DNF 是用 Python 编写的，因为它有各种各样的插件，因此它的设计是可扩展的。但是 有一个 Fedora 基本容器镜像替代品，它使用一个较小的名为 [microdnf](https://github.com/rpm-software-management/microdnf) 的包管理器，使用 C 编写。要在 Dockerfile 中使用这个最小的镜像，`FROM` 行应该如下所示：



```
FROM registry.fedoraproject.org/fedora-minimal:30
```

如果你的镜像不需要像 Python 这样的典型 DNF 依赖项，例如，如果你在制作 NodeJS 镜像时，那么这是一个重要的节省项。


### 在一个层中安装和清理


为了节省空间，使用 `dnf clean all` 或其 microdnf 等效的 `microdnf clean all` 删除仓库元数据非常重要。但是你不应该分两步执行此操作，因为这实际上会将这些文件保存在容器镜像中，然后在另一层中将其标记为删除。要正确地执行此操作，你应该像这样一步完成安装和清理：



```
FROM registry.fedoraproject.org/fedora-minimal:30
RUN microdnf install nodejs && microdnf clean all
```

### 使用 microdnf 进行模块化


模块化是一种给你选择不同堆栈版本的方法。例如，你可能需要在项目中用非 LTS 的 NodeJS v11，旧的 LTS NodeJS v8 用于另一个，最新的 LTS NodeJS v10 用于另一个。你可以使用冒号指定流。



```
# dnf module list
# dnf module install nodejs:8
```

`dnf module install` 命令意味着两个命令，一个启用流，另一个是从它安装 nodejs。



```
# dnf module enable nodejs:8
# dnf install nodejs
```

尽管 `microdnf` 不提供与模块化相关的任何命令，但是可以启用带有配置文件的模块，并且 libdnf（被 microdnf 使用）[似乎](https://bugzilla.redhat.com/show_bug.cgi?id=1575626)支持模块化流。该文件看起来像这样：



```
/etc/dnf/modules.d/nodejs.module
[nodejs]
name=nodejs
stream=8
profiles=
state=enabled
```

使用模块化的 `microdnf` 的完整 Dockerfile 如下所示：



```
FROM registry.fedoraproject.org/fedora-minimal:30
RUN \
   echo -e "[nodejs]\nname=nodejs\nstream=8\nprofiles=\nstate=enabled\n" > /etc/dnf/modules.d/nodejs.module && \
   microdnf install nodejs zopfli findutils busybox && \
   microdnf clean all
```

### 多阶段构建


在许多情况下，你可能需要大量的无需用于运行软件的构建时依赖项，例如构建一个静态链接依赖项的 Go 二进制文件。多阶段构建是分离应用构建和应用运行时的有效方法。


例如，下面的 Dockerfile 构建了一个 Go 应用 [confd](https://github.com/kelseyhightower/confd)。



```
# building container
FROM registry.fedoraproject.org/fedora-minimal AS build
RUN mkdir /go && microdnf install golang && microdnf clean all
WORKDIR /go
RUN export GOPATH=/go; CGO_ENABLED=0 go get github.com/kelseyhightower/confd

FROM registry.fedoraproject.org/fedora-minimal
WORKDIR /
COPY --from=build /go/bin/confd /usr/local/bin
CMD ["confd"]
```

通过在 `FROM` 指令之后添加 `AS` 并从基本容器镜像中添加另一个 `FROM` 然后使用 `COPY --from=` 指令将内容从*构建*的容器复制到第二个容器来完成多阶段构建。


可以使用 `podman` 构建并运行此 Dockerfile：



```
$ podman build -t myconfd .
$ podman run -it myconfd
```



---


via: <https://fedoramagazine.org/building-smaller-container-images/>


作者：[Muayyad Alsadi](https://fedoramagazine.org/author/alsadi/) 选题：[lujun9972](https://github.com/lujun9972) 译者：[geekpi](https://github.com/geekpi) 校对：[wxy](https://github.com/wxy)


本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出


OK
Linux Containers have become a popular topic, making sure that a container image is not bigger than it should be is considered as a good practice. This article give some tips on how to create smaller Fedora container images.

### microdnf

Fedora’s DNF is written in Python and and it’s designed to be extensible as it has wide range of plugins. But Fedora has an alternative base container image which uses an smaller package manager called [microdnf](https://github.com/rpm-software-management/microdnf) written in C. To use this minimal image in a Dockerfile the FROM line should look like this:

FROM registry.fedoraproject.org/fedora-minimal:30

This is an important saving if your image does not need typical DNF dependencies like Python. For example, if you are making a NodeJS image.

### Install and Clean up in one layer

To save space it’s important to remove repos meta data using *dnf clean all* or its microdnf equivalent *microdnf clean all*. But you should not do this in two steps because that would actually store those files in a container image layer then mark them for deletion in another layer. To do it properly you should do the installation and cleanup in one step like this

FROM registry.fedoraproject.org/fedora-minimal:30

RUN microdnf install nodejs && microdnf clean all

### Modularity with microdnf

Modularity is a way to offer you different versions of a stack to choose from. For example you might want non-LTS NodeJS version 11 for a project and old LTS NodeJS version 8 for another and latest LTS NodeJS version 10 for another. You can specify which stream using colon

# dnf module list

# dnf module install nodejs:8

The *dnf module install* command implies two commands one that enables the stream and one that install nodejs from it.

# dnf module enable nodejs:8

# dnf install nodejs

Although microdnf does not offer any command related to modularity, it is possible to enable a module with a configuation file, and libdnf (which microdnf uses) [seems](https://bugzilla.redhat.com/show_bug.cgi?id=1575626) to support modularity streams. The file looks like this

/etc/dnf/modules.d/nodejs.module

[nodejs]

name=nodejs

stream=8

profiles=

state=enabled

A full Dockerfile using modularity with microdnf looks like this:

FROM registry.fedoraproject.org/fedora-minimal:30

RUN \

echo -e "[nodejs]\nname=nodejs\nstream=8\nprofiles=\nstate=enabled\n" > /etc/dnf/modules.d/nodejs.module && \

microdnf install nodejs zopfli findutils busybox && \

microdnf clean all

### Multi-staged builds

In many cases you might have tons of build-time dependencies that are not needed to run the software for example building a Go binary, which statically link dependencies. Multi-stage build are an efficient way to separate the application build and the application runtime.

For example the Dockerfile below builds [confd](https://github.com/kelseyhightower/confd) a Go application.

# building container

FROM registry.fedoraproject.org/fedora-minimal AS build

RUN mkdir /go && microdnf install golang && microdnf clean all

WORKDIR /go

RUN export GOPATH=/go; CGO_ENABLED=0 go get github.com/kelseyhightower/confd

FROM registry.fedoraproject.org/fedora-minimal

WORKDIR /

COPY --from=build /go/bin/confd /usr/local/bin

CMD ["confd"]

The multi-stage build is done by adding *AS* after the *FROM* instruction and by having another *FROM* from a base container image then using C*OPY –from=* instruction to copy content from the *build* container to the second container.

This Dockerfile can then be built and run using podman

$ podman build -t myconfd .

$ podman run -it myconfd

## Bashar Subeh

Thank you. You’re so helpful

## Ard Righ

It would be nice to see this with Buildah and Podman commands as an alternative to relying on a Dockerfile.

## Ard Righ

Something like this will work using Buildah commands

export newcontainer=$(buildah from registry.fedoraproject.org/fedora-minimal:30)

echo $newcontainer

echo -e “[nodejs]\nname=nodejs\nstream=8\nprofiles=\nstate=enabled\n” > nodejs.module

buildah copy $newcontainer nodejs.module /etc/dnf/modules.d/

buildah run $newcontainer — microdnf install nodejs zopfli findutils busybox

buildah run $newcontainer — microdnf clean all

buildah commit $newcontainer nodejs

buildah inspect nodejs

## aairey

Wouldn’t the extra buildah run create an extra layer? In the dockerfile we did

.

## Muayyad Alsadi

If I’m not mistaken, buildah do not do auto-commits, it only adds a layer when you commit. and since he did it once, it would add a single layer.

## Ard Righ

Buildah doesn’t write the layers until you commit. So all the operations before the commit are a single layer. You can check this by using

on the build image.

## Raphael Groner

Why not just use pypy to optimize normal dnf?

## Muayyad Alsadi

microdnf does not depend on python, if you are creating a nodejs images that would be a big saving. but pypy would still pull python-related packages. There is a 170MB difference (47% smaller nodejs image).

## Luiz

I don’t understand so much about theses topics, But I think it’s awesome.

## Sébastien Wilmet

Nice article, I’ve learned new things.

Another thing that I would like to do with containers, when developing them or when I need to debug one, is to plug in an extra layer with all the development tools that I need, plus my bashrc (especially for aliases) and my configuration for other tools. Is there an easy way to do that?

Because with a minimal image, the test/debug experience is quite horrible IMHO, for example if bash-completion is not installed, etc.