FATAL: could not connect to the primary server: connection to server at "x.x.x.x", port 5432 failed: session is read-only about patroni HOT 3 CLOSED

most likely patroni doesn't allow replication from replica instead of leader

To be precise, standby-leader wants to replicate from the primary. Yes.

i need to replicate the data from standby patroni cluster to rollback cluster which is still in read-only session until it got promoted

There is no real need to do it. What you should better do - gracefully convert cluster in the DC1 to standby as it is described here: #1660 (comment)
In fact, you can immediately put host and port to standby_cluster section in DC1, so that after promoting standby cluster in DC2 the cluster from DC1 will start replicating.

from patroni.

Thanks for the explanation! really appreciate it

But in my use case, the service has very big transaction. if i immediately create fail forward replication from DC2 to DC1, it maybe works but maybe not as well, hard to guarantee it.

So instead of doing this, we create separate rollback cluster in DC1 separate from existing cluster in DC1
so actually we do have migration project between DC 1 and DC2

so the topology is
existing patroni cluster DC1 (leader) -> standby patroni cluster DC2 (standby leader / replica from existing leader DC1) -> rollback patroni cluster DC1 (standby leader / replica from standby leader DC2)
those 2 DC has separate dcs.

with above topology, if anything goes wrong in DC2, we can immediately promote rollback cluster in DC1 and we don't need to worries about the transaction WAL because at the beginning we do have replication slot between DC2 and rollback cluster DC1.

Thanks

from patroni.

hi @CyberDem0n sorry to tag you again, about this PR, is there any information about when will it get the approval? Thanks!

from patroni.