[k8s] postgresql 운영 - stateful (펌질)

https://gravitational.com/blog/running-postgresql-on-kubernetes/

postgres를 그냥 k8s에서 운영했다가 데이터 손실되었다고 한다.

stateful(https://kubernetes.io/docs/concepts/workloads/controllers/statefulset/) 써서 HA를 유지하는 것이 좋다는 얘기가 있다. 

stateful은 중요하다.

Using StatefulSets

StatefulSets are valuable for applications that require one or more of the following.

• Stable, unique network identifiers.
• Stable, persistent storage.
• Ordered, graceful deployment and scaling.
• Ordered, graceful deletion and termination.
• Ordered, automated rolling updates.

In the above, stable is synonymous with persistence across Pod (re)scheduling. If an application doesn’t require any stable identifiers or ordered deployment, deletion, or scaling, you should deploy your application with a controller that provides a set of stateless replicas. Controllers such as Deployment or ReplicaSet may be better suited to your stateless needs.

Limitations

• StatefulSet was a beta resource prior to 1.9 and not available in any Kubernetes release prior to 1.5.
• As with all alpha/beta resources, you can disable StatefulSet through the --runtime-config option passed to the apiserver.
• The storage for a given Pod must either be provisioned by a PersistentVolume Provisioner based on the requested storage class, or pre-provisioned by an admin.
• Deleting and/or scaling a StatefulSet down will not delete the volumes associated with the StatefulSet. This is done to ensure data safety, which is generally more valuable than an automatic purge of all related StatefulSet resources.
• StatefulSets currently require a Headless Service to be responsible for the network identity of the Pods. You are responsible for creating this Service.