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either: those standby nodes are really standby and no applications are running on them until they are in standby
Interesting question. In AS4/5/6 you can do this with https://community.jboss.org/wiki/HASingletonDeployer and have physically guaranteed single deployment -- that would solve your problem.
The nodes with loadfactor = 0 are standby nodes they will be used no other nodes are available
I suspect there is something wrong with the information, we have seen previously that loadfactor =0 actually means that node is in error state and request won't be forwarded.
if no loadfactor !=0 servers are left, all loadfactor =0 servers will be equally load-balanced?
That would be the case yes, new sessions would be load-balanced.
If this cannot be achieved with mod_cluster what specific open source products - modules, proxy/balancers can be used to achieve this?)
I would leave mod_cluster as is and focus more on having only single deployment if you say its not cluster ready.
I wonder if this can be solved by domain making sure there is always a single deployment at least one in a cluster? Can you try?
I need to think little more about this.
Radoslav Husar thanks for your answer. Can you elaborate more on this "I wonder if this can be solved by domain making sure there is always a single deployment at least one in a cluster?"?
I will have a look.
Actually a great and fun way to implement this (from Paul) would be to:
- Write a custom mod_cluster metric
- that will leverage the HA Singleton service to
- return load of 1 (or 100) for the node where the service is deployed
- and return load of 0 (disabled) for when the node is not the master.
- The application would have to be deployed on all nodes, but it will be always accessed only on 1 node.
Want to give it a try implementing?