Plesk UI is showing error 502 periodically: child exited on signal 11 (SIGSEGV) after seconds from start

Symptoms

• Plesk UI is showing error 502 periodically.
• The following error can be found in /var/log/sw-cp-server/sw-engine.log:

  CONFIG_TEXT: [16:41:08] WARNING: [pool plesk] child 32080 exited on signal 11 (SIGSEGV) after 13.923568 seconds from start

• The following error can be found in /var/log/sw-cp-server/error_log:

  CONFIG_TEXT: 16:41:08 [error] 11608#0: *771 recv() failed (104: Connection reset by peer) while reading response header from upstream, client: 203.0.113.2, server: , request: "GET /smb/ HTTP/1.1", upstream: "fastcgi://unix:/var/run/sw-engine.sock:", host: "192.0.2.2:8443"

Cause

Server is unable to serve the requests due to high amount of connections. Possibly, server is under brute-force attack.

Resolution

Login to the server over SSH and increase pm.max_children value in /etc/sw-engine/pool.d/plesk.conf file and restart sw-engine and sw-cp-server services:

# grep max_children /etc/sw-engine/pool.d/plesk.conf
pm.max_children = 26
# service sw-engine restart
# service sw-cp-server restart

In case there is a brute-force, also install Fail2Ban via Tools & Settings > Updates & Upgrades > Add/Remove Components or via the command line to protect the server from brute-force attack.