this post was submitted on 24 Apr 2024
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Those are all fair, also the entire open-vswitch setup is very clunky. I always avoid the UI and just edit /etc/network/interfaces directly, especially for vlan networks. I dislike that it wants 3 nodes but I understand, still 2 nodes in the homelab is pretty reasonable. I wish in general the HA was more configurable, robust, and intuitive.
For HA you are always going to need 3 nodes at least. Most HA systems need 5 or more
Does that need to be true though? For like true "counting in how many 9's" HA of course. But there's nothing technically preventing high availability in 2 nodes; if the storage is shared and there's a process to keep the memory in sync it should be possible with 2 nodes have some degree of high availability, even if it's with big warnings.
The problem with 2 nodes is there is no way to identity which node has the issue. From the hosts perspective all it "knows" is that the other node isn't reachable. Technically it could assume that it is the functional one but there is also the possibility that both machines assume they are the working one and then spin up the same VM.
You can cluster two nodes but as soon as one node can't reach the other everything freezes to prevent loss of consensus.
The reason I suggest 5 nodes is because 3 only gives the possibility for one node to fail. If one fails and then the remaining 2 can't sort out what is happening the cluster freezes to prevent loss of consensus. Also having 5 machines means you have more flexibility.
I also want to point out that you need fast networking for HA but I'm sure you already know that.