[pgpool-general: 5944] Re: Split-brain remedy

[Pierre Timmermans]

To prevent this split brain scenario (caused by a network partition) you can use the configuration trusted_servers. This setting is a list of servers that pgpool can use to determine if a node is suffering a network partition or not. If a node cannot reach any of the servers in the list, then it will assume it is isolated (by a network partition) and will not promote itself to master.
In general, when you have only two nodes, it is not safe to do an automatic failover I believe.  Unless you have some kind of fencing mechanism (means: you can shutdown and prevent a failed node to come back after a failure).
Pierre 

    On Tuesday, February 27, 2018, 7:58:55 PM GMT+1, Alexander Dorogensky <amazinglifetime at gmail.com> wrote:  
 
 Hi All,

I have a 10.0.0.1/10.0.0.2 master/hot standby configuration with streaming replication, where each node runs pgpool with watchdog enabled and postgres.

I shut down the network interface on 10.0.0.1 and wait until 10.0.0.2 triggers failover and promotes itself to master through my failover script.

Now the watchdogs on 10.0.0.1 and 10.0.0.2 are out of sync, have conflicting views on which node has failed and both think they are master.

When I bring back the network interface on 10.0.0.1, 'show pool_nodes' says that 10.0.0.1 is master/up and 10.0.0.2 is standby/down. 

I want 10.0.0.1 to be standby and 10.0.0.2 to be master. 

I've been playing with the failover script.. e.g.

if (default network gateway is pingable) {
    shut down pgpool and postgres
} else if (this node is standby) {
    promote this node to master
    create a job that will run every minute and try to recover failed node (base backup) 
    cancel the job upon successful recovery
} 

Can you please help me with this? Any ideas would be highly appreciated.

Regards, Alex
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