The main limitation in what you are asking here (and in any PXC cluster) would be that all the nodes must be able to communicate with each other. So, providing you can work out the networking/firewall details between all these nodes, then you can connect them.

One caveat would be commit latency would increase on the GCE cluster by adding an external node. How much depends on how far away the extra node is.

A second caveat would be that this setup tool will create a new cluster with the nodes in GCE. You’d have to add the other node later, which would copy the data from the new cluster to the older node. If you want the data sync to go in the opposite direction, you’d need to ensure the old node was a cluster first, and then connect the GCE nodes to it.

A third caveat would be what will happen when the GCE nodes and your remote node lose network connectivity for whatever reason. What do you want to happen in terms of node failure? I’d consider this carefully based on how Galera handles node failure and network partitions before putting something like this into production.

Is it possible to add external node(s) to this cluster? I mean for example I have a working server somewhere and want to keep it, but also want to set up an XtraDB cluster on Google Compute Engine and want the old server to be the part of the new cluster.

Many thanks,

Jozsef Toth