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added best practices on labels (#4854) 

Signed-off-by: Victoria Bialas <victoria.bialas@docker.com>
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Victoria Bialas 2017-10-10 08:43:23 -07:00 committed by GitHub
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engine/userguide/eng-image/dockerfile_best-practices.md
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@ -156,8 +156,7 @@ while still being a full distribution.
You can add labels to your image to help organize images by project, record
licensing information, to aid in automation, or for other reasons. For each
label, add a line beginning with `LABEL` and with one or more key-value pairs.
The following examples show the different acceptable formats. Explanatory comments
are included inline.
The following examples show the different acceptable formats. Explanatory comments are included inline.
>**Note**: If your string contains spaces, it must be quoted **or** the spaces
must be escaped. If your string contains inner quote characters (`"`), escape
@ -169,10 +168,21 @@ LABEL com.example.version="0.0.1-beta"
LABEL vendor="ACME Incorporated"
LABEL com.example.release-date="2015-02-12"
LABEL com.example.version.is-production=""
```
An image can have more than one label. To specify multiple labels, Docker
recommends combining labels into a single `LABEL` instruction where possible.
Each `LABEL` instruction produces a new layer which can result in an inefficient
image if you use many labels. This example results in a single image layer.
```conf
# Set multiple labels on one line
LABEL com.example.version="0.0.1-beta" com.example.release-date="2015-02-12"
```
The above can also be written as:
```conf
# Set multiple labels at once, using line-continuation characters to break long lines
LABEL vendor=ACME\ Incorporated \
com.example.is-beta= \
@ -181,10 +191,11 @@ LABEL vendor=ACME\ Incorporated \
com.example.release-date="2015-02-12"
```
See [Understanding object labels](../labels-custom-metadata.md) for
guidelines about acceptable label keys and values. For information about
querying labels, refer to the items related to filtering in
[Managing labels on objects](../labels-custom-metadata.md#managing-labels-on-objects).
See [Understanding object labels](/engine/userguide/labels-custom-metadata.md)
for guidelines about acceptable label keys and values. For information about
querying labels, refer to the items related to filtering in [Managing labels on
objects](../labels-custom-metadata.md#managing-labels-on-objects). See also
[LABEL](/engine/reference/builder/#label) in the Dockerfile reference.
### RUN