docs migration: Container Lifecycle Hooks into Concepts (#2564)

* initial commit for structure * migrate Container Lifecycle Hooks and related files to Concepts * update Concepts ToC * fix formatting * Formatting tweaks * comment out What's next * remove What's next * Begin rewrite of container-lifecycle-hooks.md * incremental update to edit * Split Container Lifecycle Hooks into container-lifecycle-hooks.md and container-environment.md; change all referring links. * Add concept template to volumes.md and images.md * Apply changes for steveperry-53 feedback. * fix format issue * tweak formatting * fix Concepts ToC * update links * add back changes to Concepts ToC * fix a link * update links
2017-04-25 10:36:59 -07:00
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+---
+assignees:
+- mikedanese
+- thockin
+title: Container Environment Variables
+---
+
+{% capture overview %}
+
+This page describes the resources available to Containers in the Container environment. 
+
+{% endcapture %}
+
+{:toc}
+
+{% capture body %}
+
+## Container environment
+
+The Kubernetes Container environment provides several important resources to Containers:
+
+* A filesystem, which is a combination of an [image](/docs/concepts/containers/images) and one or more [volumes](/docs/concepts/storage/volumes).
+* Information about the Container itself.
+* Information about other objects in the cluster.
+
+### Container information
+
+The *hostname* of a Container is the name of the Pod in which the Container is running.
+It is available through the `hostname` command or the
+[`gethostname`](http://man7.org/linux/man-pages/man2/gethostname.2.html)
+function call in libc.
+
+The Pod name and namespace are available as environment variables through the
+[downward API](docs/tasks/configure-pod-container/downward-api-volume-expose-pod-information).
+
+User defined environment variables from the Pod definition are also available to the Container,
+as are any environment variables specified statically in the Docker image.
+
+### Cluster information
+
+A list of all services that were running when a Container was created are available to that Container as environment variables.
+Those environment variables match the syntax of Docker links.
+
+For a service named *foo* that maps to a container port named *bar*,
+the following variables are defined:
+
+```shell
+FOO_SERVICE_HOST=<the host the service is running on>
+FOO_SERVICE_PORT=<the port the service is running on>
+```
+
+Services have dedicated IP addresses and are available to the Container via DNS,
+if [DNS addon](http://releases.k8s.io/{{page.githubbranch}}/cluster/addons/dns/) is enabled. 
+
+{% endcapture %}
+
+{% capture whatsnext %}
+
+* Learn more about [Container lifecycle hooks](/docs/concepts/containers/container-lifecycle-hooks.md).
+* Get hands-on experience
+  [attaching handlers to Container lifecycle events](/docs/tasks/configure-pod-container/attach-handler-lifecycle-event/).
+
+{% endcapture %}
+
+{% include templates/concept.md %}