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Update info on dockerignore, add link to multistage builds (#4953)

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Misty Stanley-Jones 2017-10-13 15:59:24 -07:00 committed by GitHub
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engine/userguide/eng-image/dockerfile_best-practices.md
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@ -17,13 +17,11 @@ 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
`Dockerfile`s. We strongly suggest you follow these recommendations (in fact,
if you’re creating an Official Image, you *must* adhere to these practices).
Inc. and the Docker community for building efficient images. To see many of
these practices and recommendations in action, check out the Dockerfile for
[buildpack-deps](https://github.com/docker-library/buildpack-deps/blob/master/jessie/Dockerfile).
You can see many of these practices and recommendations in action in the [buildpack-deps `Dockerfile`](https://github.com/docker-library/buildpack-deps/blob/master/jessie/Dockerfile).
> Note: for more detailed explanations of any of the Dockerfile commands
> **Note**: for more detailed explanations of any of the Dockerfile commands
>mentioned here, visit the [Dockerfile Reference](../../reference/builder.md) page.
## General guidelines and recommendations
@ -40,12 +38,36 @@ stateless fashion.
### Use a .dockerignore file
In most cases, it's best to put each Dockerfile in an empty directory. Then,
add to that directory only the files needed for building the Dockerfile. To
increase the build's performance, you can exclude files and directories by
adding a `.dockerignore` file to that directory as well. This file supports
exclusion patterns similar to `.gitignore` files. For information on creating one,
see the [.dockerignore file](../../reference/builder.md#dockerignore-file).
The current working directory where you are located when you issue a
`docker build` command is called the _build context_, and the `Dockerfile` must
be somewhere within this build context. By default, it is assumed to be in the
current directory, but you can specify a different location by using the `-f`
flag. Regardless of where the `Dockerfile` actually lives, all of the recursive
contents of files and directories in the current directory are sent to the
Docker daemon as the _build context_. Inadvertently including files that are not
necessary for building the image results in a larger build context and larger
image size. These in turn can increase build time, time to pull and push the
image, and the runtime size of containers. To see how big your build context
is, look for a message like the following, when you build your `Dockerfile`.
```none
Sending build context to Docker daemon 187.8MB
```
To exclude files which are not relevant to the build, without restructuring your
source repisotiry, use a `.dockerignore` file. This file supports
exclusion patterns similar to `.gitignore` files. For information on creating
one, see the [.dockerignore file](../../reference/builder.md#dockerignore-file).
In addition to using a `.dockerignore` file, check out the information below
on [multi-stage builds](#use-multi-stage-builds).
### Use multi-stage builds
If you use Docker 17.05 or higher, you can use
[multi-stage builds](/engine/userguide/eng-image/multistage-build.md) to
drastically reduce the size of your final image, without the need to
jump through hoops to reduce the number of intermediate layers or remove
intermediate files during the build.
### Avoid installing unnecessary packages