In the wiki i found the information, for an HA cluster you need at least 3 nodes. Can anyone tell me why i can't use this with 2?
Regards
fireon
Regards
fireon
Last edited:
[Solved] Why do i need 3 Nodes for an HA Cluster?
- Thread starter fireon
- Start date
Re: Why do i need 3 Nodes for an HA Cluster?
A cluster needs to know which nodes are accessible/available (turned on and networking is fine) and which ones arent (power failure, network failure... something). If you have 3 nodes and one node fails, both remaining nodes can still communicate with each other and "reach the conclusion" that node #3 is unavailable because both #1 and #2 cant talk to it. If the cluster was only 2 nodes and both nodes cant see each other... both nodes will consider the other node offline and take meassures accordingly. Now if both are actually still in working condition and "only" the network between them broke down, they will both try to start all VMs that need to be kept running which is very likely to result in complete corruption of the VMs disk images on the storage (assuming the storage is still reachable).
This is not a very technical explanation, but you get the gist.
A cluster needs to know which nodes are accessible/available (turned on and networking is fine) and which ones arent (power failure, network failure... something). If you have 3 nodes and one node fails, both remaining nodes can still communicate with each other and "reach the conclusion" that node #3 is unavailable because both #1 and #2 cant talk to it. If the cluster was only 2 nodes and both nodes cant see each other... both nodes will consider the other node offline and take meassures accordingly. Now if both are actually still in working condition and "only" the network between them broke down, they will both try to start all VMs that need to be kept running which is very likely to result in complete corruption of the VMs disk images on the storage (assuming the storage is still reachable).
This is not a very technical explanation, but you get the gist.
Re: Why do i need 3 Nodes for an HA Cluster?
Thank you very much, now I understand it. It was absolutly not clear for me before. This explains the configuration of an DRBD.
Regards
fireon
Thank you very much, now I understand it. It was absolutly not clear for me before. This explains the configuration of an DRBD.
Regards
fireon