Tomcat 8.5.9 restart is really slow on my CentOS 7.2 droplet

Slow start up times for Tomcat are often related to Java’s SecureRandom implementation. By default, it uses /dev/random as an entropy source. This can be slow as it uses system events to gather entropy (e.g. disk reads, key presses, etc). As the urandom manpage states:

When the entropy pool is empty, reads from /dev/random will block until additional environmental noise is gathered.

One work around is to use /dev/urandom instead as it does not block. This is defined in your JAVA_OPTS That can be set in a number of places depending on how you set up Tomcat in the first place. It will usually be the init script or systemd service file used to start Tomcat.

-Djava.security.egd=file:/dev/./urandom

See this tutorial for more information.

Another option is to use haveged to generate more entropy. On CentOS, you can do so with:

yum install haveged
systemctl start haveged
systemctl enable haveged

For more information on how haveged works, check out this tutorial:

• How to Setup Additional Entropy for Cloud Servers Using Haveged