Add chapter about labels

slides/intro-fullday.yml

@@ -31,6 +31,7 @@ chapters:
   - intro/Publishing_To_Docker_Hub.md
   - intro/Dockerfile_Tips.md
 - - intro/Naming_And_Inspecting.md
+  - intro/Labels.md
   - intro/Getting_Inside.md
   - intro/Container_Networking_Basics.md
   - intro/Network_Drivers.md

slides/intro/Labels.md

@@ -0,0 +1,82 @@
+# Labels
+
+* Labels allow to attach arbitrary metadata to containers.
+
+* Labels are key/value pairs.
+
+* They are specified at container creation.
+
+* You can query them with `docker inspect`.
+
+* They can also be used as filters with some commands (e.g. `docker ps`).
+
+---
+
+## Using labels
+
+Let's create a few containers with a label `owner`.
+
+```bash
+docker run -d -l owner=alice nginx
+docker run -d -l owner=bob nginx
+docker run -d -l owner nginx
+```
+
+We didn't specify a value for the `owner` label in the last example.
+
+This is equivalent to setting the value to be an empty string.
+
+---
+
+## Querying labels
+
+We can view the labels with `docker inspect`.
+
+```bash
+$ docker inspect $(docker ps -lq) | grep -A3 Labels
+            "Labels": {
+                "maintainer": "NGINX Docker Maintainers <docker-maint@nginx.com>",
+                "owner": ""
+            },
+```
+
+We can use the `--format` flag to list the value of a label.
+
+```bash
+$ docker inspect $(docker ps -q) --format 'OWNER={{.Config.Labels.owner}}'
+```
+
+---
+
+## Using labels to select containers
+
+We can list containers having a specific label.
+
+```bash
+$ docker ps --filter label=owner
+```
+
+Or we can list containers having a specific label with a specific value.
+
+```bash
+$ docker ps --filter label=owner=alice
+```
+
+---
+
+## Use-cases for labels
+
+
+* HTTP vhost of a web app or web service.
+
+  (The label is used to generate the configuration for NGINX, HAProxy, etc.)
+
+* Backup schedule for a stateful service.
+
+  (The label is used by a cron job to determine if/when to backup container data.)
+
+* Service ownership.
+
+  (To determine internal cross-billing, or who to page in case of outage.)
+
+* etc.