On 2021-02-17 04:22, Mutuku Ndeti wrote: > Thank you. > > I agree with you. Single master, with a standby replica, seems easier to > manage. Is there a way to automatically promote the standby, when the > active master fails? Is it feasible to have 2 instances of the > application, writing onto the same DB, reason for two instances of the > application is to allow for redundancy/load balancing. > Again, not being PostgreSQL-specific, it is possible to have an active/standby master node with shared storage (ex fibrechannel, iscsi... it can only be mounted on only one node at any given time and it's the cluster's responsibility to ensure the other node has unmounted properly). This is ideal when dealing with fully redundant storage arrays, and fairly simple to setup on the cluster side. Attaching additional slaves to an active/standby cluster is also usually simpler since there is just one server/replication log. Another solution is to have a replication ring (ex. A replicates to B, B replicates to A). With such setup it is very important writes only ever happen on a single node, and is easiest to do so by using a floating IP that can only be reached from one node at any given time (again it's the cluster's responsibility to ensure the floating IP is never on both). This method may require a more complex configuration to ensure updates are consistent and to keep additional slaves synchronized to the cluster. Also since both servers have a permanent IP it is important to ensure no updates are made directly to them. The warm side can still be used for read-only access though (with a very small lag). In either case, there is likely some configuration needed. This page seems to list a few projects that may make your cluster setup much easier: https://wiki.postgresql.org/wiki/Replication,_Clustering,_and_Connection_Pooling Regards, -- Thomas
