Persistence in a cluster.
WHAT THE PROBLEM IS
Pods move between nodes, and local disk does not follow.
WHAT A PERSISTENT VOLUME IS
A piece of storage in the cluster.
WHAT A CLAIM IS
A request for storage, which a volume satisfies.
WHY THE SEPARATION
Applications request what they need without knowing how it is provided.
WHAT A STORAGE CLASS IS
A description of a kind of storage, enabling automatic provisioning.
WHAT DYNAMIC PROVISIONING DOES
Creates the storage when a claim is made.
WHAT ACCESS MODES MEAN
Whether one node or many can mount it, and whether for writing.
WHY THAT MATTERS
Most block storage can only be attached to one node at a time.
WHAT THAT IMPLIES
A deployment with several replicas cannot share such a volume.
WHAT TO USE FOR SHARED ACCESS
A network filesystem, accepting the performance cost.
WHAT A STATEFULSET PROVIDES
Stable names, and a volume per instance that follows it.
WHERE THAT IS NEEDED
Databases and anything where instances are not interchangeable.
WHAT TO CHECK ABOUT RECLAIM POLICY
What happens to storage when the claim is deleted.
WHY
A policy of deletion removes the data.
WHAT TO SET FOR ANYTHING IMPORTANT
Retain.
WHAT TO PLAN REGARDLESS
Backups, which the cluster does not provide.
