Upgrade myriarch

Upgrade the server, the database schema and the updaters without downtime.

This page is planned for v0.3.0.

It will appear here when it is ready. Until then, these pages cover the closest ground:

Upgrade from v0.1.0 to v0.2.0: the notes for the move to v0.2.0.
Release notes: what changed in every release.
Helm chart and values: the chart that carries the server.
High availability: how long a failover takes and the settings that bound it.