I have elastic 7.2 installed in kubernetes (via the elastic helm chart, secure example). How can I upgrade this to 7.3 (preferably in a rolling way)?
The upgrade steps are the same as any non kubernetes managed cluster. The helm chart does help you with a few of the steps though.
Make sure to read through https://www.elastic.co/guide/en/elasticsearch/reference/7.3/setup-upgrade.html and https://www.elastic.co/guide/en/elasticsearch/reference/7.3/rolling-upgrades.html. The most important step being to test this first in a dev environment.
From the rolling upgrade guide steps 4 through to 11 will be covered by the helm chart. Instead of "4. Shut down a single node" and "5. Upgrade the node you shut down" you will instead be setting
imageTag: 7.3.0 to initiate the rolling upgrade. If you are using the default
imageTag values you will instead just upgrade the helm chart version to 7.3.0.
The helm chart configures the statefulset with a readinessProbe that waits for the cluster health to be
green in between node upgrades. This automates the "stop each node and upgrade them while waiting for the cluster to become healthy again" part of the upgrade guide.