The operator allows changing the PostgreSQL version used in a cluster while applications are running against it.
Only upgrades for PostgreSQL minor releases are supported.
Rolling upgrades are started when:
the user changes the
imageNameattribute of the cluster specification;
a change in the PostgreSQL configuration requires a restart to be applied;
a change on the
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 in-place updates are enabled).
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 (
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.
Automated updates (
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.
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
switchover as part of the rolling update procedure.
Manual updates (
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:
kubectl cnpg promote [cluster] [new_primary]
You can trigger a restart with:
kubectl cnpg restart [cluster] [current_primary]
You can find more information in the
cnpg plugin page.