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018282f392
This was discussed and agreed in #246. It will probably break a few outstanding PRs as well as a few external links but it's for the better good long term.
83 lines
1.6 KiB
Markdown
83 lines
1.6 KiB
Markdown
# Labels
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* Labels allow to attach arbitrary metadata to containers.
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* Labels are key/value pairs.
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* They are specified at container creation.
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* You can query them with `docker inspect`.
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* They can also be used as filters with some commands (e.g. `docker ps`).
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---
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## Using labels
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Let's create a few containers with a label `owner`.
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```bash
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docker run -d -l owner=alice nginx
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docker run -d -l owner=bob nginx
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docker run -d -l owner nginx
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```
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We didn't specify a value for the `owner` label in the last example.
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This is equivalent to setting the value to be an empty string.
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---
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## Querying labels
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We can view the labels with `docker inspect`.
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```bash
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$ docker inspect $(docker ps -lq) | grep -A3 Labels
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"Labels": {
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"maintainer": "NGINX Docker Maintainers <docker-maint@nginx.com>",
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"owner": ""
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},
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```
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We can use the `--format` flag to list the value of a label.
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```bash
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$ docker inspect $(docker ps -q) --format 'OWNER={{.Config.Labels.owner}}'
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```
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---
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## Using labels to select containers
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We can list containers having a specific label.
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```bash
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$ docker ps --filter label=owner
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```
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Or we can list containers having a specific label with a specific value.
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```bash
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$ docker ps --filter label=owner=alice
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```
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---
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## Use-cases for labels
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* HTTP vhost of a web app or web service.
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(The label is used to generate the configuration for NGINX, HAProxy, etc.)
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* Backup schedule for a stateful service.
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(The label is used by a cron job to determine if/when to backup container data.)
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* Service ownership.
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(To determine internal cross-billing, or who to page in case of outage.)
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* etc.
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