Environment becomes unstable after number of file descriptors has steadily increased

Issue

• A Liferay environment with a frontal element has become unstable after running for a few days.
• Checking the system's health, there has been a steady increase of open file descriptors.

Environment

• Liferay DXP 7.4
• Liferay Quarterly Release 2023.Q3, 2023.Q4

Resolution

• This behavior can occur when there's a frontal element to Liferay communicating via AJP. 
• The connections between them will show as open file descriptors in the system.
  • They can be displayed with the command lsof -p $java_pid.
• For example, Tomcat can connect to a frontal element by configuring in the file $TOMCAT_HOME/conf/server.xml the element

  <Connector protocol="AJP/1.3" [...] />

• The Connector timeout attributes connectionTimeout and keepAliveTimeout might not be set, so they'll have a default infinite value. This can lead to an increasing number of established connections between the frontal making Liferay unstable.
• Make sure to establish the connectionTimeout and/or keepAliveTimeout attributes with values adequate to your environment.

Additional Information

• See Apache Tomcat 9 Configuration Reference for definitions of connectionTimeout and keepAliveTimeout .
• See Timeouts HowTo for examples and reference values.