Configuring Multiple JVM Instances in Apache Tomcat (Single Installation)

Running multiple JVM instances in Apache Tomcat using a single installation can help optimize resource utilization while keeping administration simpler. This guide will walk you through the steps to configure multiple JVMs within a single Tomcat installation.

---

✅ Why Use Multiple JVMs in a Single Tomcat Installation?

• Efficient Resource Utilization: Use the same Tomcat binaries while running separate JVM instances.
• Application Isolation: Each application runs in its dedicated JVM instance.
• Simplified Management: Maintain one Tomcat installation instead of multiple copies.
• Better Load Balancing: Spread requests across different JVMs for performance optimization.

---

🔧 Steps to Configure Multiple JVMs in One Tomcat Installation

1️⃣ Create Separate CATALINA_BASE Directories

Since we will use the same CATALINA_HOME, we need separate CATALINA_BASE directories for each instance. This ensures that each instance has its own configuration, logs, and web applications, preventing conflicts.

mkdir /opt/tomcat-instance1
mkdir /opt/tomcat-instance2
cp -r /opt/tomcat/conf /opt/tomcat-instance1/
cp -r /opt/tomcat/conf /opt/tomcat-instance2/
cp -r /opt/tomcat/logs /opt/tomcat-instance1/
cp -r /opt/tomcat/logs /opt/tomcat-instance2/
cp -r /opt/tomcat/temp /opt/tomcat-instance1/
cp -r /opt/tomcat/temp /opt/tomcat-instance2/
cp -r /opt/tomcat/webapps /opt/tomcat-instance1/
cp -r /opt/tomcat/webapps /opt/tomcat-instance2/
cp -r /opt/tomcat/work /opt/tomcat-instance1/
cp -r /opt/tomcat/work /opt/tomcat-instance2/

Now, each instance will have its own configurations and logs, allowing them to function independently.

---

2️⃣ Set Up Environment Variables

Each Tomcat instance needs a unique environment setup to control which JVM it runs on and to assign specific memory allocations.

Instance 1 (setenv.sh):

export CATALINA_HOME=/opt/tomcat
export CATALINA_BASE=/opt/tomcat-instance1
export JAVA_HOME=/usr/lib/jvm/java-11-openjdk
export CATALINA_OPTS="-Xms512m -Xmx1024m -Djava.awt.headless=true"
export CATALINA_PID=/opt/tomcat-instance1/temp/tomcat.pid

Instance 2 (setenv.sh):

export CATALINA_HOME=/opt/tomcat
export CATALINA_BASE=/opt/tomcat-instance2
export JAVA_HOME=/usr/lib/jvm/java-17-openjdk
export CATALINA_OPTS="-Xms256m -Xmx512m -Djava.awt.headless=true"
export CATALINA_PID=/opt/tomcat-instance2/temp/tomcat.pid

This ensures each Tomcat instance runs with its own Java version and memory settings, providing better resource control and application isolation.

---

3️⃣ Modify Server Configuration (server.xml)

Each instance must listen on different ports to avoid conflicts. Modifying server.xml allows each instance to have unique connectors, ensuring smooth operation.

Instance 1 (/opt/tomcat-instance1/conf/server.xml):

<Server port="8005" shutdown="SHUTDOWN">
    <Connector port="8080" protocol="HTTP/1.1" connectionTimeout="20000" redirectPort="8443" />
    <Engine name="Catalina" defaultHost="localhost">
        <Host name="localhost" appBase="webapps" unpackWARs="true" autoDeploy="true"/>
    </Engine>
</Server>

Instance 2 (/opt/tomcat-instance2/conf/server.xml):

<Server port="8105" shutdown="SHUTDOWN">
    <Connector port="8180" protocol="HTTP/1.1" connectionTimeout="20000" redirectPort="8543" />
    <Engine name="Catalina" defaultHost="localhost">
        <Host name="localhost" appBase="webapps" unpackWARs="true" autoDeploy="true"/>
    </Engine>
</Server>

This prevents port conflicts and allows each instance to handle requests independently.

---

4️⃣ Start & Stop Tomcat Instances

Using separate startup and shutdown scripts ensures that each Tomcat instance runs independently.

Start Instance 1:

CATALINA_BASE=/opt/tomcat-instance1 /opt/tomcat/bin/startup.sh

Start Instance 2:

CATALINA_BASE=/opt/tomcat-instance2 /opt/tomcat/bin/startup.sh

Stopping instances:

CATALINA_BASE=/opt/tomcat-instance1 /opt/tomcat/bin/shutdown.sh

CATALINA_BASE=/opt/tomcat-instance2 /opt/tomcat/bin/shutdown.sh

This allows smooth operation and maintenance of each instance without affecting the others.

---

🎯 Best Practices

✅ Assign unique ports for HTTP, AJP, and Shutdown ports to avoid conflicts.
✅ Monitor JVM performance using JVisualVM or JConsole for optimal resource usage.
✅ Configure separate log directories for each instance for easier debugging and maintenance.
✅ Use systemd service files to automate the startup and shutdown process for better reliability.

---

🔥 Conclusion

By following this guide, you can successfully configure multiple JVM instances using a single Tomcat installation to enhance scalability and isolate applications effectively.

🤝 Connect With Us

Are you looking for certified Tomcat professionals or need expert guidance on your project? We are here to help!

🔹 Get Certified Candidates: Hire skilled professionals with Tomcat expertise.

🔹 Project Consultation: Get best practices and hands-on support for seamless implementation.

📞 Contact Us Now

💼 Discuss Your Project