Help with UDP load balancing passive health checks

[Pawel Fraczek]

Hi, I'm trying to building a syslog load balancer and I'm running into
issues with the failover of UDP messages. TCP works just fine, when the
server goes down, all messages failover to the active server. But with UDP,
that does not happen. Maybe someone can point me to what I'm doing wrong.
Below is the config.

upstream syssrv {
 server 192.168.167.108:5500 max_fails=2 fail_timeout=15s;
 server 192.168.167.109:5500 max_fails=2 fail_timeout=15s;
 }
 server {
 listen 5500;
 proxy_protocol on;
 proxy_pass syssrv;
 proxy_timeout 1s;
 proxy_connect_timeout 1s;
 }
 server {
 listen 5500 udp;
 proxy_pass syssrv;
 proxy_timeout 1s;
 proxy_connect_timeout 1s;
 proxy_bind $remote_addr transparent;
 }
}

I have a script that enumerates each message (n) like this "Testing -proto:
udp - n"

I see both servers getting the message when they are online (even - odd
numbers) but when one goes down, once server continues to only get the even
numbers, so I'm losing 50% of the messages.

I tried to debug the setup and I see nginx marking that the udp packets
timed out. I see this:

2022/02/22 20:05:13 [info] 21362#21362: *777 udp client
192.168.167.101:51529 connected to 0.0.0.0:5500
2022/02/22 20:05:13 [info] 21362#21362: *777 udp proxy
192.168.167.101:34912 connected to 192.168.167.108:5500
2022/02/22 20:05:13 [info] 21362#21362: *779 udp client
192.168.167.101:53862 connected to 0.0.0.0:5500
2022/02/22 20:05:13 [info] 21362#21362: *779 udp proxy
192.168.167.101:35506 connected to 192.168.167.109:5500

Then this:

2022/02/22 20:05:14 [info] 21362#21362: *771 udp timed out, packets
from/to client:1/0, bytes from/to client:145/0, bytes from/to
upstream:0/145

But, it's not redirecting the connection to the healthy server. This seems
pretty simple but any ideas what I'm doing wrong? It would seem that the
non-commercial version should be able to do this, no?

Any help is appreciated. I also tried to add a backup, but it doesn't work
with UDP

-- 
Pawel
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