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201 lines
6.6 KiB
Markdown
201 lines
6.6 KiB
Markdown
<!--[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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[menu.main]
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parent = "mn_use_docker"
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+++
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<![end-metadata]-->
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# Apply custom metadata
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You can apply metadata to your images, containers, or daemons via
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labels. Metadata can serve a wide range of uses. Use labels to add notes or
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licensing information to an image or to identify a host.
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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>` / `<value>` must be
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unique to avoid overwriting. If you specify the same `key` several times but with
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different values, newer labels overwrite previous labels. Docker uses
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the last `key=value` you supply.
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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 are new in Docker 1.6.0
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## Label keys (namespaces)
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Docker puts no hard restrictions on the label `key` you. However, labels with
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simple keys can conflict. For example, you can categorize your images by using a
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chip "architecture" label:
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LABEL architecture="amd64"
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LABEL architecture="ARMv7"
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But a user can label images by building architectural style:
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LABEL architecture="Art Nouveau"
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To prevent naming conflicts, Docker namespaces label keys using a reverse domain
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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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- The `com.docker.*`, `io.docker.*` and `org.dockerproject.*` namespaces are
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reserved for Docker's 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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- Keys should start *and* end with an alpha numeric character
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- Keys may not contain consecutive dots or dashes.
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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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These are guidelines and Docker does not *enforce* them. Failing following these
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guidelines can result in conflicting labels. If you're building a tool that uses
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labels, you *should* use namespaces for your label keys.
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## Store structured data in labels
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Label values can contain any data type that can be stored as a string. For
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example, consider this JSON:
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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 should implement this.
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## Add labels to images; the `LABEL` instruction
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Adding labels to an image:
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LABEL [<namespace>.]<key>[=<value>] ...
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The `LABEL` instruction adds a label to your image, optionally setting its value.
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Use surrounding quotes or backslashes for labels that contain
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white space character:
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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="0.0.1-beta"
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LABEL com.example.release-date="2015-02-12"
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The `LABEL` instruction supports setting multiple labels in a single instruction
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using this notation:
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LABEL com.example.version="0.0.1-beta" com.example.release-date="2015-02-12"
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Wrapping is allowed 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.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.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.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 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 a `color` label of `blue`:
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$ docker ps --filter "label=color=blue"
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List all images with `vendor` `ACME`:
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$ docker images --filter "label=vendor=ACME"
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## Daemon labels
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docker daemon \
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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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Images: 672
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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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Execution Driver: native-0.2
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Logging Driver: json-file
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Kernel Version: 3.13.0-32-generic
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Operating System: Ubuntu 14.04.1 LTS
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CPUs: 1
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Total Memory: 994.1 MiB
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Name: docker.example.com
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ID: RC3P:JTCT:32YS:XYSB:YUBG:VFED:AAJZ:W3YW:76XO:D7NN:TEVU:UCRW
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Debug mode (server): false
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Debug mode (client): true
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File Descriptors: 11
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Goroutines: 14
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EventsListeners: 0
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Init Path: /usr/bin/docker
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Docker Root Dir: /var/lib/docker
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WARNING: No swap limit support
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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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