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Restructure content about Docker object labels
A few points of work: - Took the topic out of the left-hand nav and made it reachable from the User guide intro - Condensed the topic's contents, presenting only conceptual info and pointing instead to the command-line references for each type of object - Added brief information about the `LABELS` keyword to the Dockerfile reference A big part of the point is to establish a pattern of thinking and use around how Docker uses labels and what they mean in different contexts. Signed-off-by: Misty Stanley-Jones <misty@docker.com>
This commit is contained in:
Misty Stanley-Jones
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3 changed files with 145 additions and 202 deletions
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@ -134,6 +134,43 @@ image. We recommend the [Debian image](https://hub.docker.com/_/debian/)
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since it’s very tightly controlled and kept minimal (currently under 150 mb),
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while still being a full distribution.
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### LABEL
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[Understanding object labels](../labels-custom-metadata.md)
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You can add labels to your image to help organize images by project, record
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licensing information, to aid in automation, or for other reasons. For each
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label, add a line beginning with `LABEL` and with one or more key-value pairs.
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The following examples show the different acceptable formats. Explanatory comments
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are included inline.
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>**Note**: If your string contains spaces, it must be quoted **or** the spaces
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must be escaped. If your string contains inner quote characters (`"`), escape
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them as well.
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```dockerfile
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# Set one or more individual labels
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LABEL com.example.version="0.0.1-beta"
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LABEL vendor="ACME Incorporated"
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LABEL com.example.release-date="2015-02-12"
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LABEL com.example.version.is-production=""
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# Set multiple labels on one line
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LABEL com.example.version="0.0.1-beta" com.example.release-date="2015-02-12"
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# Set multiple labels at once, using line-continuation characters to break long lines
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LABEL vendor=ACME\ Incorporated \
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com.example.is-beta= \
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com.example.is-production="" \
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com.example.version="0.0.1-beta" \
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com.example.release-date="2015-02-12"
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```
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See [Understanding object labels](../labels-custom-metadata.md) for
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guidelines about acceptable label keys and values. For information about
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querying labels, refer to the items related to filtering in
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[Managing labels on objects](../labels-custom-metadata.md#managing-labels-on-objects).
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### RUN
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[Dockerfile reference for the RUN instruction](../../reference/builder.md#run)
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@ -142,7 +179,7 @@ As always, to make your `Dockerfile` more readable, understandable, and
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maintainable, split long or complex `RUN` statements on multiple lines separated
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with backslashes.
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### apt-get
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#### apt-get
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Probably the most common use-case for `RUN` is an application of `apt-get`. The
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`RUN apt-get` command, because it installs packages, has several gotchas to look
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@ -3,6 +3,7 @@
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title = "Introduction"
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description = "Introduction to user guide"
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keywords = ["docker, introduction, documentation, about, technology, docker.io, user, guide, user's, manual, platform, framework, home, intro"]
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identifier = "engine_guide_intro"
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[menu.main]
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parent="engine_guide"
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+++
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@ -64,6 +65,25 @@ learning how to manage data, volumes and mounts inside our containers.
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Go to [Managing Data in Containers](../tutorials/dockervolumes.md).
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## Managing metadata (labels) for Docker objects
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Labels are a mechanism for applying metadata to Docker objects, including:
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- Images
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- Containers
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- Local daemons
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- Volumes
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- Networks
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- Swarm nodes
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- Swarm services
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You can use labels to organize your images, record licensing information, annotate
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relationships between containers, volumes, and networks, or in any way that makes
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sense for your business or application.
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Go to [Managing Docker object labels](labels-custom-metadata.md).
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## Docker products that complement Engine
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Often, one powerful technology spawns many other inventions that make that easier to get to, easier to use, and more powerful. These spawned things share one common characteristic: they augment the central technology. The following Docker products expand on the core Docker Engine functions.
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@ -1,230 +1,116 @@
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<!--[metadata]>
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+++
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title = "Apply custom metadata"
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description = "Learn how to work with custom metadata in Docker, using labels."
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keywords = ["Usage, user guide, labels, metadata, docker, documentation, examples, annotating"]
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title = "Managing Docker object labels"
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description = "Description of labels, which are used to manage metadata on Docker objects."
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keywords = ["Usage, user guide, labels, metadata, docker, documentation, examples, annotating"]
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[menu.main]
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parent = "engine_guide"
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parent = "engine_guide_intro"
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weight=90
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+++
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<![end-metadata]-->
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# Apply custom metadata
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# About labels
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You can apply metadata to your images, containers, volumes, networks, nodes, services or daemons via
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labels. Labels serve a wide range of uses, such as adding notes or licensing
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information to an image, or to identify a host.
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Labels are a mechanism for applying metadata to Docker objects, including:
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A label is a `<key>` / `<value>` pair. Docker stores the label values as
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*strings*. You can specify multiple labels but each `<key>` must be
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unique or the value will be overwritten. If you specify the same `key` several
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times but with different values, newer labels overwrite previous labels. Docker
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uses the last `key=value` you supply.
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- Images
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- Containers
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- Local daemons
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- Volumes
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- Networks
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- Swarm nodes
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- Swarm services
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>**Note:** Support for daemon-labels was added in Docker 1.4.1. Labels on
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>containers and images were added in Docker 1.6.0
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You can use labels to organize your images, record licensing information, annotate
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relationships between containers, volumes, and networks, or in any way that makes
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sense for your business or application.
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## Label keys (namespaces)
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# Label keys and values
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Docker puts no hard restrictions on the `key` used for a label. However, using
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simple keys can easily lead to conflicts. For example, you have chosen to
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categorize your images by CPU architecture using "architecture" labels in
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your Dockerfiles:
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A label is a key-value pair, stored as a string. You can specify multiple labels
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for an object, but each key-value pair must be unique within an object. If the
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same key is given multiple values, the most-recently-written value overwrites
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all previous values.
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LABEL architecture="amd64"
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## Key format recommendations
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LABEL architecture="ARMv7"
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A label _key_ is the left-hand side of the key-value pair. Keys are alphanumeric
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strings which may contain periods (`.`) and hyphens (`-`). Most Docker users use
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images created by other organizations, and the following guidelines help to
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prevent inadvertent duplication of labels across objects, especially if you plan
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to use labels as a mechanism for automation.
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Another user may apply the same label based on a building's "architecture":
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- Authors of third-party tools should prefix each label key with the
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reverse DNS notation of a domain they own, such as `com.example.some-label`.
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LABEL architecture="Art Nouveau"
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To prevent naming conflicts, Docker recommends using namespaces to label keys
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using reverse domain notation. Use the following guidelines to name your keys:
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- All (third-party) tools should prefix their keys with the
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reverse DNS notation of a domain controlled by the author. For
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example, `com.example.some-label`.
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- Do not use a domain in your label key without the domain owner's permission.
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- The `com.docker.*`, `io.docker.*` and `org.dockerproject.*` namespaces are
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reserved for Docker's internal use.
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reserved by Docker for internal use.
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- Keys should only consist of lower-cased alphanumeric characters,
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dots and dashes (for example, `[a-z0-9-.]`).
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- Label keys should begin and end with a lower-case letter and should only
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contain lower-case alphanumeric characters, the period character (`.`), and
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the hyphen character (`-`). Consecutive periods or hyphens are not allowed.
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- Keys should start *and* end with an alpha numeric character.
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- The period character (`.`) separates namespace "fields". Label keys without
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namespaces are reserved for CLI use, allowing users of the CLI to interactively
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label Docker objects using shorter typing-friendly strings.
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- Keys may not contain consecutive dots or dashes.
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These guidelines are not currently enforced and additional guidelines may apply
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to specific use cases.
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- Keys *without* namespace (dots) are reserved for CLI use. This allows end-
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users to add metadata to their containers and images without having to type
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cumbersome namespaces on the command-line.
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## Value guidelines
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Label values can contain any data type that can be represented as a string,
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including (but not limited to) JSON, XML, CSV, or YAML. The only requirement is
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that the value be serialized to a string first, using a mechanism specific to
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the type of structure. For instance, to serialize JSON into a string, you might
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use the `JSON.stringify()` JavaScript method.
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Since Docker does not deserialize the value, you cannot treat a JSON or XML
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document as a nested structure when querying or filtering by label value unless
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you build this functionality into third-party tooling.
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# Managing labels on objects
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Each type of object with support for labels has mechanisms for adding and
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managing them and using them as they relate to that type of object. These links
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provide a good place to start learning about how you can use labels in your
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Docker deployments.
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Labels on images, containers, local daemons, volumes, and networks are static for
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the lifetime of the object. To change these labels you must recreate the object.
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Labels on swarm nodes and services can be updated dynamically.
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These are simply guidelines and Docker does not *enforce* them. However, for
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the benefit of the community, you *should* use namespaces for your label keys.
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- Images and containers
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- [Adding labels to images](../reference/builder.md#label)
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- [Overriding a container's labels at runtime](../reference/commandline/run.md#set-metadata-on-container-l-label-label-file)
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- [Inspecting labels on images or containers](../reference/commandline/inspect.md)
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- [Filtering images by label](../reference/commandline/inspect.md#filtering)
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- [Filtering containers by label](../reference/commandline/ps.md#filtering)
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- Local Docker daemons
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- [Adding labels to a Docker daemon at runtime](../reference/commandline/dockerd.md)
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- [Inspecting a Docker daemon's labels](../reference/commandline/info.md)
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## Store structured data in labels
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- Volumes
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- [Adding labels to volumes](../reference/commandline/volume_create.md)
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- [Inspecting a volume's labels](../reference/commandline/volume_inspect.md)
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- [Filtering volumes by label](../reference/commandline/volume_ls.md#filtering)
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Label values can contain any data type as long as it can be represented as a
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string. For example, consider this JSON document:
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- Networks
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- [Adding labels to a network](../reference/commandline/network_create.md)
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- [Inspecting a network's labels](../reference/commandline/network_inspect.md)
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- [Filtering networks by label](../reference/commandline/network_ls.md#filtering)
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- Swarm nodes
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- [Adding or updating a swarm node's labels](../reference/commandline/node_update.md#add-label-metadata-to-a-node)
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- [Inspecting a swarm node's labels](../reference/commandline/node_inspect.md)
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- [Filtering swarm nodes by label](../reference/commandline/node_ls.md#filtering)
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{
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"Description": "A containerized foobar",
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"Usage": "docker run --rm example/foobar [args]",
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"License": "GPL",
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"Version": "0.0.1-beta",
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"aBoolean": true,
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"aNumber" : 0.01234,
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"aNestedArray": ["a", "b", "c"]
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}
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You can store this struct in a label by serializing it to a string first:
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LABEL com.example.image-specs="{\"Description\":\"A containerized foobar\",\"Usage\":\"docker run --rm example\\/foobar [args]\",\"License\":\"GPL\",\"Version\":\"0.0.1-beta\",\"aBoolean\":true,\"aNumber\":0.01234,\"aNestedArray\":[\"a\",\"b\",\"c\"]}"
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While it is *possible* to store structured data in label values, Docker treats
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this data as a 'regular' string. This means that Docker doesn't offer ways to
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query (filter) based on nested properties. If your tool needs to filter on
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nested properties, the tool itself needs to implement this functionality.
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## Add labels to images
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To add labels to an image, use the `LABEL` instruction in your Dockerfile:
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LABEL [<namespace>.]<key>=<value> ...
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The `LABEL` instruction adds a label to your image. A `LABEL` consists of a `<key>`
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and a `<value>`.
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Use an empty string for labels that don't have a `<value>`,
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Use surrounding quotes or backslashes for labels that contain
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white space characters in the `<value>`:
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LABEL vendor=ACME\ Incorporated
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LABEL com.example.version.is-beta=
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LABEL com.example.version.is-production=""
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LABEL com.example.version="0.0.1-beta"
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LABEL com.example.release-date="2015-02-12"
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The `LABEL` instruction also supports setting multiple `<key>` / `<value>` pairs
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in a single instruction:
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LABEL com.example.version="0.0.1-beta" com.example.release-date="2015-02-12"
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Long lines can be split up by using a backslash (`\`) as continuation marker:
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LABEL vendor=ACME\ Incorporated \
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com.example.is-beta= \
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com.example.is-production="" \
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com.example.version="0.0.1-beta" \
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com.example.release-date="2015-02-12"
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Docker recommends you add multiple labels in a single `LABEL` instruction. Using
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individual instructions for each label can result in an inefficient image. This
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is because each `LABEL` instruction in a Dockerfile produces a new IMAGE layer.
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You can view the labels via the `docker inspect` command:
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$ docker inspect 4fa6e0f0c678
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...
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"Labels": {
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"vendor": "ACME Incorporated",
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"com.example.is-beta": "",
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"com.example.is-production": "",
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"com.example.version": "0.0.1-beta",
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"com.example.release-date": "2015-02-12"
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}
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...
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# Inspect labels on container
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$ docker inspect -f "{{json .Config.Labels }}" 4fa6e0f0c678
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{"Vendor":"ACME Incorporated","com.example.is-beta":"", "com.example.is-production":"", "com.example.version":"0.0.1-beta","com.example.release-date":"2015-02-12"}
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# Inspect labels on images
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$ docker inspect -f "{{json .ContainerConfig.Labels }}" myimage
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## Query labels
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Besides storing metadata, you can filter images and containers by label. To list all
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running containers that have the `com.example.is-beta` label:
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# List all running containers that have a `com.example.is-beta` label
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$ docker ps --filter "label=com.example.is-beta"
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List all running containers with the label `color` that have a value `blue`:
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$ docker ps --filter "label=color=blue"
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List all images with the label `vendor` that have the value `ACME`:
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$ docker images --filter "label=vendor=ACME"
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## Container labels
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docker run \
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-d \
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--label com.example.group="webservers" \
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--label com.example.environment="production" \
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busybox \
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top
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Please refer to the [Query labels](#query-labels) section above for information
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on how to query labels set on a container.
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## Daemon labels
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dockerd \
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--dns 8.8.8.8 \
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--dns 8.8.4.4 \
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-H unix:///var/run/docker.sock \
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--label com.example.environment="production" \
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--label com.example.storage="ssd"
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These labels appear as part of the `docker info` output for the daemon:
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$ docker -D info
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Containers: 12
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Running: 5
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Paused: 2
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Stopped: 5
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Images: 672
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Server Version: 1.9.0
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Storage Driver: aufs
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Root Dir: /var/lib/docker/aufs
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Backing Filesystem: extfs
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Dirs: 697
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Dirperm1 Supported: true
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Execution Driver: native-0.2
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Logging Driver: json-file
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Kernel Version: 3.19.0-22-generic
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Operating System: Ubuntu 15.04
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CPUs: 24
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Total Memory: 62.86 GiB
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Name: docker
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ID: I54V:OLXT:HVMM:TPKO:JPHQ:CQCD:JNLC:O3BZ:4ZVJ:43XJ:PFHZ:6N2S
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Debug mode (server): true
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File Descriptors: 59
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Goroutines: 159
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System Time: 2015-09-23T14:04:20.699842089+08:00
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EventsListeners: 0
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Init SHA1:
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Init Path: /usr/bin/docker
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Docker Root Dir: /var/lib/docker
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Http Proxy: http://test:test@localhost:8080
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Https Proxy: https://test:test@localhost:8080
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WARNING: No swap limit support
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Username: svendowideit
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Registry: [https://index.docker.io/v1/]
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Labels:
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com.example.environment=production
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com.example.storage=ssd
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- Swarm services
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- [Adding labels when creating a swarm service](../reference/commandline/service_create.md#set-metadata-on-a-service-l-label)
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- [Updating a swarm service's labels](../reference/commandline/service_update.md)
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- [Inspecting a swarm service's labels](../reference/commandline/service_inspect.md)
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- [Filtering swarm services by label](../reference/commandline/service_ls.md#filtering)
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