If you found that your server does not respond anything without any error message, it might be associated with the maximum number of thread in your system.
I resolved this issue by following actions.
1) Modifying /etc/security/limits.conf in my CentOS 7 server.
* hard nofile 500000 * soft nofile 500000 root hard nofile 500000 root soft nofile 500000
2) Modifying a value of maxThreads.Connector in <confluence_home_directory>/conf/server.xml
You may able to see maxThread as a member of <Connector>. The default value of maxThreads is 48 - I just modified it to 4096
<Server port="8000" shutdown="SHUTDOWN" debug="0">
<Service name="Tomcat-Standalone">
<Connector port="8090" connectionTimeout="20000" redirectPort="8443"
maxThreads="48" minSpareThreads="10"
enableLookups="false" acceptCount="10" debug="0" URIEncoding="UTF-8"
protocol="org.apache.coyote.http11.Http11NioProtocol"/>
<Engine name="Standalone" defaultHost="localhost" debug="0">
<Host name="localhost" debug="0" appBase="webapps" unpackWARs="true" autoDeploy="false" startStopThreads="4">
<Context path="" docBase="../confluence" debug="0" reloadable="false" useHttpOnly="true">
<!-- Logging configuration for Confluence is specified in confluence/WEB-INF/classes/log4j.properties -->
<Manager pathname=""/>
<Valve className="org.apache.catalina.valves.StuckThreadDetectionValve" threshold="60"/>
</Context>
<Context path="${confluence.context.path}/synchrony-proxy" docBase="../synchrony-proxy" debug="0"
reloadable="false" useHttpOnly="true">
<Valve className="org.apache.catalina.valves.StuckThreadDetectionValve" threshold="60"/>
</Context>
</Host>
</Engine>
</Service>
</Server>
Once your modification is done, you should restart your server to take effect.