HAproxy Use backup server with active servers in one backend

Question

I'm struggling with a scenario that I've searched and read so much but couldn't find anything to solve it. I have 3 servers, 2 actives and one as a standby(backup). every time one of active servers go down, the standby server will be active and traffic load balance between 2 server (not just standby server). I am able to solve this problem with two backends, BUT I need just one backend.

#### Fronend Configuration ##### 
frontend webserver 

bind 192.168.64.100:80
default_backend appserver


#### Backend Configuration #####
backend appserver 
balance roundrobin
server Node-1 192.168.64.132:80 check
server Node-2 192.168.64.133:80 check

server Node-3 192.168.64.134:80 check

I want Node-3 be the standby server. if Node-1 or Node-2 isn't accessible, Node-3 take the place

Please post your current config file and describe more about what your desired goal is. — duct_tape_coder, Feb 25 '20 at 23:09
@duct_tape_coder thank you for your response, I edited the post, tell me if you need more explanation. — Ali Kargar, Feb 25 '20 at 23:57
So you're saying if Node-1 fails, you want Node-2 and Node-3 to both run but instead you're seeing just Node-3? — duct_tape_coder, Feb 26 '20 at 01:53

score 1 · Answer 1 · answered Feb 26 '20 at 04:43

Take a look here: https://www.haproxy.com/blog/failover-and-worst-case-management-with-haproxy/

It looks like by default the backup servers only take effect when all of the primary servers are offline. So it seems like if Node-1 is down and Node-2 is still up, it should still be serving with only Node-2. If both Node-1 and Node-2 are offline, Node-3 would be used. It's possible your situation is occurring because some config is indicating that when 50% of servers are unavailable, the backup should be triggered (perhaps this is default?).

But if you look further at that page, you can set logic to trigger a backup group when a certain amount of servers in the primary fail. With only three servers in the set, I'm not sure how you'd properly accomplish that bilaterally but you could set if 1 of the 2 fails, trigger a backup of two which includes a primary. Honestly it make more sense to leverage all three in the primary group unless you pay a penalty for using it (e.g. hosted services).

frontent ft_app
 bind 10.0.0.1:80
# detect capacity issues in production farm
 acl MAIN_not_enough_capacity nb_srv(bk_app_main) le 2
# failover traffic to backup farm
 use_backend bk_app_backup if MAIN_not_enough_capacity
 default_backend bk_app_main
backend bk_app_main
 server s11 10.0.0.101:80 check
 server s12 10.0.0.102:80 check
 server s13 10.0.0.103:80 check
 server s14 10.0.0.104:80 check
backend bk_app_backup
 option allbackups
 server s21 20.0.0.101:80 check
 server s22 20.0.0.102:80 check
 server s23 20.0.0.103:80 check backup
 server s24 20.0.0.104:80 check backup

yeah I saw this, and at the first step I configured HAproxy exactly like this and worked fine, but now, I need every thiing in one backend. — Ali Kargar, Feb 27 '20 at 04:50

HAproxy Use backup server with active servers in one backend

1 Answers1