I deploy sakai server on docker and use haproxy as load balancer. I can't find the log of clustering in the docker logs command. So where is the detailed log of haproxy located?

I deploy sakai server on docker and use haproxy as load balancer. I can't find the log of clustering in the docker logs command. So where is the detailed log of haproxy located?

This is the HAProxy log and there is no other. On Docker, it is sent to stdout. You can make it more verbose by setting the level from "info" to "debug":
log stdout format raw local0 debug
It looks like health checks are failing. Can you exec a bash shell into the HAProxy container and ping the server from there?