Обсуждение: dual active 2-node cluster?

On Fri, 2018-04-13 at 03:01 -0700, Ron Watkins wrote:
> We are working to setup a production environment and as such one requirement is to have
> as few single points of failure as possible. To that end, I have been searching the web
> for how to setup a 2-node cluster where both nodes are active. The goal is to allow both
> nodes to service SQL requests (load/query) and have a load balancer in front of the
> database to allow for transparent outage and node recovery.

You'd need synchronous replication, and if you do that with two nodes,
you'll get low availability because any outage will take down the whole
system.  That's not a shortcoming, that's unavoidable.

You need at least three nodes for decent high availability, particularly
if you want load balancing.

Look into Patroni for a high availability solution.

Yours,
Laurenz Albe
-- 
Cybertec | https://www.cybertec-postgresql.com

What about a hot standby mode where secondary node is receiving all transactions in real (or near-real) time?
Is this doable? We have 2 physical nodes, not 3, so if we can do a hot-standby config with a load balancer configured
infail-over mode, that should work as long as no transactions are dropped and the secondary node is staying current
(i.e.dual commit) with the primary node? 
Does anyone know if there are any links to how to setup such a config on the web?
Ron

-----Original Message-----
From: Laurenz Albe [mailto:laurenz.albe@cybertec.at]
Sent: Friday, April 13, 2018 6:41 AM
To: Ron Watkins; pgsql-novice
Subject: Re: dual active 2-node cluster?

On Fri, 2018-04-13 at 03:01 -0700, Ron Watkins wrote:
> We are working to setup a production environment and as such one
> requirement is to have as few single points of failure as possible. To
> that end, I have been searching the web for how to setup a 2-node
> cluster where both nodes are active. The goal is to allow both nodes
> to service SQL requests (load/query) and have a load balancer in front of the database to allow for transparent
outageand node recovery. 

You'd need synchronous replication, and if you do that with two nodes, you'll get low availability because any outage
willtake down the whole system.  That's not a shortcoming, that's unavoidable. 

You need at least three nodes for decent high availability, particularly if you want load balancing.

Look into Patroni for a high availability solution.

Yours,
Laurenz Albe
--
Cybertec | https://www.cybertec-postgresql.com