Project: CloudNativePG (App Definition and Development / Database)
File: rolling_update.md

The operator allows changing the PostgreSQL version used in a cluster while applications are running against it. !!! Important Only upgrades for PostgreSQL minor releases are supported. Rolling upgrades are started when: the user changes the `imageName` attribute of the cluster specification; the is updated with a new image for the major used by the cluster; a change in the PostgreSQL configuration requires a restart to be applied; a change on the `Cluster` `.spec.resources` values a change in size of the persistent volume claim on AKS after the operator is updated, to ensure the Pods run the latest instance manager (unless ). The operator starts upgrading all the replicas, one Pod at a time, and begins from the one with the highest serial. The primary is the last node to be upgraded. Rolling updates are configurable and can be either entirely automated (`unsupervised`) or requiring human intervention (`supervised`). The upgrade keeps the CloudNativePG identity, without re-cloning the data. Pods will be deleted and created again with the same PVCs and a new image, if required. During the rolling update procedure, each service endpoints move to reflect the cluster's status, so that applications can ignore the node that is being updated. When `primaryUpdateStrategy` is set to `unsupervised`, the rolling update process is managed by Kubernetes and is entirely automated. Once the replicas have been upgraded, the selected `primaryUpdateMethod` operation will initiate on the primary. This is the default behavior. The `primaryUpdateMethod` option accepts one of the following values: `restart`: if possible, perform an automated restart of the pod where the primary instance is running. Otherwise, the restart request is ignored and a switchover issued. This is the default behavior. `switchover`: a switchover operation is automatically performed, setting the most aligned replica as the new target primary, and shutting down the former primary pod. There's no one-size-fits-all configuration for the update method, as that depends on several factors like the actual workload of your database, the requirements in terms of RPO and RTO, whether your PostgreSQL architecture is shared or shared nothing, and so on. Indeed, being PostgreSQL a primary/standby architecture database management system, the update process inevitably generates a downtime for your applications. One important aspect to consider for your context is the time it takes for your pod to download the new PostgreSQL container image, as that depends on your Kubernetes cluster settings and specifications. The `switchover` method makes sure that the promoted instance already runs the target image version of the container. The `restart` method instead might require to download the image from the origin registry after the primary pod has been shut down. It is up to you to determine whether, for your database, it is best to use `restart` or `switchover` as part of the rolling update procedure. When `primaryUpdateStrategy` is set to `supervised`, the rolling update process is suspended immediately after all replicas have been upgraded. This phase can only be completed with either a manual switchover or an in-place restart. Keep in mind that image upgrades can not be applied with an in-place restart, so a switchover is required in such cases. You can trigger a switchover with: ```bash kubectl cnpg promote [cluster] [new_primary] ``` You can trigger a restart with: ```bash kubectl cnpg restart [cluster] [current_primary] ``` You can find more information in the .