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Merge pull request #30974 from erxian/add-new-cli-argument-squash-to-docker-build

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add docs to describe experimental CLI argument --squash to docker build
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Sebastiaan van Stijn 2017-03-27 17:09:54 +02:00 committed by GitHub
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90
docs/reference/commandline/build.md
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@ -444,6 +444,8 @@ more `--add-host` flags. This example adds a static address for a host named
### Squash an image's layers (--squash) **Experimental Only**
#### Overview
Once the image is built, squash the new layers into a new image with a single
new layer. Squashing does not destroy any existing image, rather it creates a new
image with the content of the squashed layers. This effectively makes it look
@ -458,3 +460,91 @@ space.
storing two copies of the image, one for the build cache with all the cache
layers in tact, and one for the squashed version.
#### Prerequisites
The example on this page is using experimental mode in Docker 1.13.
Experimental mode can be enabled by using the `--experimental` flag when starting the Docker daemon or setting `experimental: true` in the `daemon.json` configuration file.
By default, experimental mode is disabled. To see the current configuration, use the `docker version` command.
```none
Server:
Version: 1.13.1
API version: 1.26 (minimum version 1.12)
Go version: go1.7.5
Git commit: 092cba3
Built: Wed Feb 8 06:35:24 2017
OS/Arch: linux/amd64
Experimental: false
[...]
```
To enable experimental mode, users need to restart the docker daemon with the experimental flag enabled.
#### Enable Docker experimental
Experimental features are now included in the standard Docker binaries as of version 1.13.0. For enabling experimental features, you need to start the Docker daemon with `--experimental` flag. You can also enable the daemon flag via /etc/docker/daemon.json. e.g.
```
{
"experimental": true
}
```
Then make sure the experimental flag is enabled:
```bash
$ docker version -f '{{.Server.Experimental}}'
true
```
#### Build an image with `--squash` argument
The following is an example of docker build with `--squash` argument
```Dockerfile
FROM busybox
RUN echo hello > /hello
RUN echo world >> /hello
RUN touch remove_me /remove_me
ENV HELLO world
RUN rm /remove_me
```
An image named `test` is built with `--squash` argument.
```bash
$ docker build --squash -t test .
[...]
```
If everything is right, the history will look like this:
```bash
$ docker history test
IMAGE CREATED CREATED BY SIZE COMMENT
4e10cb5b4cac 3 seconds ago 12 B merge sha256:88a7b0112a41826885df0e7072698006ee8f621c6ab99fca7fe9151d7b599702 to sha256:47bcc53f74dc94b1920f0b34f6036096526296767650f223433fe65c35f149eb
<missing> 5 minutes ago /bin/sh -c rm /remove_me 0 B
<missing> 5 minutes ago /bin/sh -c #(nop) ENV HELLO=world 0 B
<missing> 5 minutes ago /bin/sh -c touch remove_me /remove_me 0 B
<missing> 5 minutes ago /bin/sh -c echo world >> /hello 0 B
<missing> 6 minutes ago /bin/sh -c echo hello > /hello 0 B
<missing> 7 weeks ago /bin/sh -c #(nop) CMD ["sh"] 0 B
<missing> 7 weeks ago /bin/sh -c #(nop) ADD file:47ca6e777c36a4cfff 1.113 MB
```
We could find that all layer's name is `<missing>`, and there is a new layer with COMMENT `merge`.
Test the image, check for `/remove_me` being gone, make sure `hello\nworld` is in `/hello`, make sure the `HELLO` envvar's value is `world`.

1
experimental/README.md
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@ -36,6 +36,7 @@ true
* [Ipvlan Network Drivers](vlan-networks.md)
* [Docker Stacks and Distributed Application Bundles](docker-stacks-and-bundles.md)
* [Checkpoint & Restore](checkpoint-restore.md)
* [Docker build with --squash argument](docker-build-with-squash.md)
## How to comment on an experimental feature