chore(kb/ec2): promote ec2 placeholder to article with child

knowledge base/cloud computing/aws/ebs.md

@@ -0,0 +1,48 @@
+# Elastic Block Store
+
+Persistent [block storage][what is block storage?] for [EC2 Instances][ec2].
+
+1. [TL;DR](#tldr)
+1. [Further readings](#further-readings)
+   1. [Sources](#sources)
+
+## TL;DR
+
+<details>
+  <summary>Real world use cases</summary>
+
+```sh
+# Clean up unused volumes.
+aws ec2 describe-volumes --output 'text' \
+  --filters 'Name=status,Values=available' --query 'Volumes[].VolumeId' \
+| xargs -pn '1' aws ec2 delete-volume --volume-id
+```
+
+</details>
+
+## Further readings
+
+- [What is block storage?]
+
+### Sources
+
+- [Documentation]
+- [Delete Unused AWS EBS Volumes]
+- [`describe-volumes`][describe-volumes]
+- [`delete-volume`][delete-volume]
+
+<!--
+  References
+  -->
+
+<!-- Knowledge base -->
+[ec2]: ec2.md
+
+<!-- Upstream -->
+[delete-volume]: https://docs.aws.amazon.com/cli/latest/reference/ec2/delete-volume.html
+[describe-volumes]: https://docs.aws.amazon.com/cli/latest/reference/ec2/describe-volumes.html
+[documentation]: https://docs.aws.amazon.com/ebs/
+[what is block storage?]: https://aws.amazon.com/what-is/block-storage/
+
+<!-- Others -->
+[delete unused aws ebs volumes]: https://www.nops.io/unused-aws-ebs-volumes/