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Edits and fixes to Dockerfile Best Practices based on review feedback. 

Docker-DCO-1.1-Signed-off-by: Fred Lifton <fred.lifton@docker.com> (github: fredlf)
This commit is contained in:
Fred Lifton 2014-09-24 16:05:35 -07:00
parent 5e69f4a188
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3 changed files with 80 additions and 49 deletions
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69
docs/sources/articles/dockerfile_best-practices.md
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@ -2,7 +2,7 @@ page_title: Best Practices for Writing Dockerfiles
page_description: Hints, tips and guidelines for writing clean, reliable Dockerfiles
page_keywords: Examples, Usage, base image, docker, documentation, dockerfile, best practices, hub, official repo
# Best Practices for Writing `Dockerfile`s
# Best Practices for Writing Dockerfiles
## Overview
@ -14,7 +14,7 @@ specific set of instructions. You can learn the basics on the
you’re new to writing `Dockerfile`s, you should start there.
This document covers the best practices and methods recommended by Docker,
Inc. and the Docker Community for creating easy-to-use, effective
Inc. and the Docker community for creating easy-to-use, effective
`Dockerfile`s. We strongly suggest you follow these recommendations (in fact,
if you’re creating an Official Image, you *must* adhere to these practices).
@ -28,21 +28,21 @@ You can see many of these practices and recommendations in action in the [buildp
### Containers should be ephemeral
The container produced by the image your `Dockerfile` defines should be as
ephemeral as possible. “Ephemeral” here means that it can be stopped and
ephemeral as possible. By “ephemeral,” we mean that it can be stopped and
destroyed and a new one built and put in place with an absolute minimum of
set-up and configuration.
### Use a [`.dockerignore` file](https://docs.docker.com/reference/builder/#the-dockerignore-file)
### Use [a .dockerignore file](https://docs.docker.com/reference/builder/#the-dockerignore-file)
For faster uploading and efficiency during `docker build`, you should make use
of a `.dockerignore` file to exclude files or directories from the build
For faster uploading and efficiency during `docker build`, you should use
a `.dockerignore` file to exclude files or directories from the build
context and final image. For example, unless`.git` is needed by your build
process or scripts, you should add it to `.dockerignore`, which can save many
megabytes worth of upload time.
### Avoid installing unnecessary packages
You should avoid installing extra or unnecessary packages just because they
In order to reduce complexity, dependencies, file sizes and build times, you should avoid installing extra or unnecessary packages just because they
might be “nice to have.” For example, you don’t need to include a text editor
in a database image.
@ -112,33 +112,40 @@ the command string itself will be used to find a match.
Once the cache is invalidated, all subsequent `Dockerfile` commands will
generate new images and the cache will not be used.
bzr \
cvs \
git \
mercurial \
subversion
## The `Dockerfile` instructions
This section contains specific recommendations for the correct usage of the
various instructions contained in a `Dockerfile`.
Below you'll find recommendations for the best way to write the
various instructions available for use in a `Dockerfile`.
### [`FROM`](https://docs.docker.com/reference/builder/#from)
Whenever possible, use Official Repositories as the basis for your image. We
recommend the [Debian image](https://registry.hub.docker.com/_/debian/) since
it’s very tightly controlled and kept extremely minimal (currently under 100
mb), while still being a full distribution.
Whenever possible, use current Official Repositories as the basis for your
image. We recommend the [Debian image](https://registry.hub.docker.com/_/debian/)
since it’s very tightly controlled and kept extremely minimal (currently under
100 mb), while still being a full distribution.
### [`RUN`](https://docs.docker.com/reference/builder/#run)
As always, to make your `Dockerfile` more readable, understandable, and
maintainable, put long or complex `RUN` statements on multiple lines separated with
backslashes.
maintainable, put long or complex `RUN` statements on multiple lines separate
with backslashes.
Probably the most common use-case for `RUN` is an application of `apt-get`.
Probably the most common use-case for `RUN` is an application of `apt-get`
When using `apt-get`, here a few things to keep in mind:
* Don’t do `RUN apt-get update` on a single line. This will cause
caching issues if the referenced archive gets updated, which will make your
subsequent `apt-get install` fail without comment.
* For the most part, to keep your code more readable and maintainable, avoid
`RUN apt-get install -y package-foo && apt-get install -y package-bar`.
* For the most part, to keep your code more readable and maintainable, avoid instructions like:
RUN apt-get install -y package-foo && apt-get install -y package-bar
* Avoid `RUN apt-get upgrade` or `dist-upgrade`, since many of the “essential”
packages from the base images will fail to upgrade inside an unprivileged
@ -146,8 +153,11 @@ container. If a base package is out of date, you should contact its
maintainers. If you know there’s a particular package, `foo`, that needs to be
updated, use `apt-get install -y foo` and it will update automatically.
* Do use `RUN apt-get update && apt-get install -y package-bar package-foo
package-baz`. Writing the instruction this way not only makes it easier to read
* Do write something like:
`RUN apt-get update && apt-get install -y package-bar package-foo package-baz`.
Writing the instruction this way not only makes it easier to read
and maintain, but also, by including `apt-get update`, ensures that the cache
will naturally be busted and the latest versions will be installed with no
further coding or manual intervention required.
@ -273,9 +283,14 @@ auto-extraction capability, you should always use `COPY`.
The best use for `ENTRYPOINT` is as a helper script. Using `ENTRYPOINT` for
other tasks can make your code harder to understand. For example,
`docker run -it official-image bash` is much easier to understand than
`docker run -it --entrypoint bash official-image -i`, especially for Docker
beginners.
....docker run -it official-image bash
is much easier to understand than
....docker run -it --entrypoint bash official-image -i
especially for Docker beginners.
In order to avoid a situation where commands are run without clear visibility
to the user, make sure your script ends with something like `exec "$@"`. After
@ -305,8 +320,8 @@ fi
exec "$@"
```
That script then gets copied into the container and the run via `ENTRYPOINT` on
container startup:
That script then gets copied into the container and run via `ENTRYPOINT` on
container startup:
COPY ./docker-entrypoint.sh /
ENTRYPOINT ["/docker-entrypoint.sh"]
@ -324,7 +339,7 @@ If a service can run without privileges, use `USER` to change to a non-root
user. Start by creating the user and group in the `Dockerfile` with something
like `RUN groupadd -r postgres && useradd -r -g postgres postgres`.
>**Note** that users/groups in an image get assigned a non-deterministic
>**Note** Users and groups in an image get a non-deterministic
>UID/GID in that the “next” UID/GID gets assigned regardless of image
>rebuilds. So, if it’s critical, you should assign an explicit UID/GID.
@ -334,7 +349,7 @@ you absolutely need functionality similar to `sudo` (e.g., initializing the
daemon as root but running it as non-root), you may be able to use
[“gosu”](https://github.com/tianon/gosu).
Lastly, to reduce layers and complexity, try to minimize switching `USER` back
Lastly, to reduce layers and complexity, avoid switching `USER` back
and forth frequently.
### [`WORKDIR`](https://docs.docker.com/reference/builder/#workdir)

51
docs/sources/docker-hub/official_repos.md
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@ -14,7 +14,8 @@ practices for image creation generally.
This document consists of two major sections:
* A list of expected files, resources and supporting items for your image
* A list of expected files, resources and supporting items for your image,
along with best practices for creating those items
* Examples embodying those practices
## Expected Files & Resources
@ -30,7 +31,7 @@ If the repo is private or has otherwise limited access, you must provide a
means of at least “read-only” access for both general users and for the
docker-library maintainers, who need access for review and building purposes.
### A `Dockerfile`
### A Dockerfile
Complete information on `Dockerfile`s can be found in the [Reference section](https://docs.docker.com/reference/builder/).
We also have a page discussing [best practices for writing `Dockerfile`s](/articles/dockerfile_best-practices).
@ -38,9 +39,9 @@ Your `Dockerfile` should adhere to the following:
* It must be written either by using `FROM scratch` or be based on another,
established Official Image.
* It must follow `Dockerfile` best practices. These are discussed in the
[Best Practices document](/articles/dockerfile_best-practices). In addition,
Docker engineer Michael Crosby has a good discussion of Dockerfiles in
* It must follow `Dockerfile` best practices. These are discussed on the
[best practices page](/articles/dockerfile_best-practices). In addition,
Docker engineer Michael Crosby has some good tips for Dockerfiles in
this [blog post](http://crosbymichael.com/dockerfile-best-practices-take-2.html).
While [`ONBUILD` triggers](https://docs.docker.com/reference/builder/#onbuild)
@ -49,7 +50,7 @@ are not required, if you choose to use them you should:
* Build both `ONBUILD` and non-`ONBUILD` images, with the `ONBUILD` image
built `FROM` the non-`ONBUILD` image.
* The `ONBUILD` image should be specifically tagged, for example, `ruby:
latest`and `ruby:onbuild`, or `ruby:2` and `ruby:2-onbuild`.
latest`and `ruby:onbuild`, or `ruby:2` and `ruby:2-onbuild`
### A short description
@ -59,7 +60,7 @@ should also:
* Be named `README-short.txt`
* Reside in the repo for the “latest” tag
* Not exceed 200 characters.
* Not exceed 200 characters
### A logo
@ -69,20 +70,21 @@ file should have the following characteristics:
* Be named `logo.png`
* Should reside in the repo for the “latest” tag
* Should be 200px min. in one dimension, 200px max. in the other.
* Should fit inside a 200px square, maximized in one dimension (preferably the
width)
* Square or wide (landscape) is preferred over tall (portrait), but exceptions
can be made based on the logo needed.
can be made based on the logo needed
### A long description
Include a comprehensive description of your image (in markdown format). Only
one description is required; you don’t need additional descriptions for each
tag. The file should also:
Include a comprehensive description of your image (in markdown format, GitHub
flavor preferred). Only one description is required; you don’t need additional
descriptions for each tag. The file should also:
* Be named `README.md`
* Reside in the repo for the “latest” tag
* Be no longer than absolutely necessary, while still addressing all the
content requirements.
content requirements
In terms of content, the long description must include the following sections:
@ -95,21 +97,22 @@ In terms of content, the long description must include the following sections:
This section should provide:
* an overview of the software contained in the image, similar to the
introduction in a Wikipedia entry,
introduction in a Wikipedia entry
* a selection of links to outside resources that help to describe the software,
* a selection of links to outside resources that help to describe the software
* a *mandatory* link to the `Dockerfile`.
* a *mandatory* link to the `Dockerfile`
#### How-to/usage
A section that describes how to run and use the image, including common use
cases and example `Dockerfile`s (if applicable). Try to provide clear,step-by-
cases and example `Dockerfile`s (if applicable). Try to provide clear, step-by-
step instructions wherever possible.
##### Issues & Contribution Info
In this part, point users to any resources that can help them contribute to the
project. Include contribution guidelines and any specific instructions related
to your development practices. Include a link to
##### Issues & contribution info
In this section, point users to any resources that can help them contribute to
the project. Include contribution guidelines and any specific instructions
related to your development practices. Include a link to
[Docker’s resources for contributors](https://docs.docker.com/contributing/contributing/).
Be sure to include contact info, handles, etc. for official maintainers.
@ -122,7 +125,7 @@ issue trackers, contacts, additional “how-to” information or other resources
Include a file, `LICENSE`, of any applicable license. Docker recommends using
the license of the software contained in the image, provided it allows Docker,
Inc. to legally build and distribute the image. Otherwise Docker recommends
Inc. to legally build and distribute the image. Otherwise, Docker recommends
adopting the [Expat license](http://directory.fsf.org/wiki/License:Expat).
## Examples
@ -176,3 +179,7 @@ For more examples, take a look at these repos:
* [Buildpack-deps](https://github.com/docker-library/buildpack-deps)
* ["Hello World" minimal container](https://github.com/docker-library/hello-world)
* [Node](https://github.com/docker-library/node)
## Submit your repo
Once you've checked off everything in these guidelines, and are confident your image is ready for primetime, please contact us at [partners@docker.com](mailto:partners@docker.com) to have your project considered for the Official Repos program.

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docs/theme/mkdocs/css/docs.css vendored
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@ -241,6 +241,15 @@ ol li {
margin-top: 10px;
}
.content-body h4 {
font-size: 16px;
font-weight: 400;
color: #394d54;
line-height: 1.7;
margin-bottom: 4px;
margin-top: 10px;
}
.content-body p {
font-size: 14px;
font-weight: 400;