TT - connection issue can be found in the localhost log for the day - search for - Could not open Hibernate Session for transaction
Up hikari pool size
Was due to the load balancer
Could see in error log
2022/10/21 09:25:41 [crit] 22657#0: accept4() failed (24: Too many open files)
Changed the nginx-jelastic.conf to use - connection_pool_size 512;
Changed the nginx.conf line to use - worker_rlimit_nofile 6048;
https://www.nginx.com/blog/tuning-nginx/
https://serverfault.com/questions/1003364/nginx-500-24-too-many-open-files
Could also be the proxySQL maxing out of user connections.
Found error in app server log - str-unknown.log
ERROR connecting to database [proxy.env-2601119.j.layershift.co.uk] : com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: User 'jelastic-3753417' has exceeded the 'max_user_connections' resource (current value: 1000)
See https://forums.percona.com/t/max-connect-timeout-reached-while-reaching-hostgroup/8860