HAProxy community

Synchronization of 2 HAProxy nodes


I would like to set up two haproxy’s nodes in master-master configuration. And to achieve that I would have to keep synchronizing their backends (servers status, number of connections, and so on).

I know it can be achieved using peers and stick-table, but I’m not able to find any solution suitable to me.

I’m kind of newby. Any advice or suggestion will be welcomed.

Here are my proxies conifgurations:

listen stats
mode http
stats enable

listen lorehaven
mode    tcp
balance leastconn
option  tcplog
option redispatch
timeout check 3s
timeout client 11m
timeout connect 600
timeout queue 5m
timeout server 11m
<a lot of servers>


Why do think you need synchronization, what is the use-case here?


I’m using HAProxy to load balance tcp connections. All servers in backend have maxcon set to 3.

I would like to have 2 HAProxy nodes to avoid single point of failure.

And now, if I run 2 nodes simultaneously with maxcon 3 and equip them with same servers list manually, it won’t work properly. It’s caused by nodes not being aware of each other - one doesn’t know that second one set up a connection / they will set up maximum 6 connections in sum to each server in the backend.

That’s why I want to synchronize them. I want them being aware their actions - e.g. if node A set up connection, node B updates its connection list.


I understand, you want synchronization so that maxconn/rate-limiting works correctly when both haproxy nodes are active at the same time.

That’s not supported in haproxy.

Also I personally believe this is a bad idea for a number a technical and organizational reasons.

This includes:

  • when there any issue or a broken state in the active instance, you cannot failover to the standby unit, as it will have synchronized the same state.
  • when you make a change, you cannot deploy it on the standby unit and then failover to it, with a proper rollback possibility, instead you have to deploy on active instances
  • there is no clear advantage of an active/active design, and it is especially senseless when you just have 2 nodes in active/active mode (because the second node is either not needed to keep up with the traffic - or if it is needed then both nodes become a single point of failure, because one node won’t be able to handle the load). If you need 16 nodes in active/active, then your point is probably performance, but with 2 nodes you really don’t have an excuse to not use active/standby
  • the delay in synchronization will lead to race conditions, imprecise and wrong behavior (because global rate-limiting simply doesn’t work)