We have citus cluster with 1 coordinator and 3 worker node and we have some problems with the coordinator node.
So can we add another coordintor node to the cluster ?
or
Can we change one of our worker node to the coordinator ?
You can add a hot standby for the coordinator using logical replication, and later once it catches up you can promote the standby to be the primary.
You can check out the docs for these scenarios, sharing some of the sections below. Make sure you read the correct version of this page, depending on your Citus version.
https://docs.citusdata.com/en/v12.1/admin_guide/cluster_management.html#adding-a-coordinator
https://docs.citusdata.com/en/v12.1/admin_guide/cluster_management.html#coordinator-node-failures