Master Tomcat: Install, Configure, and Deploy Multi-Instance Java Apps

Tomcat Overview

Tomcat Concept

Tomcat is an open‑source lightweight application server written in Java, part of the Apache Software Foundation. It implements Java Servlet, JSP, and EL, enabling dynamic web applications on the Java platform.

Tomcat Role

Tomcat is a Java Servlet container used to run Java web applications.

Running Java Web Applications

Servlet and JSP support: Tomcat processes servlet and JSP requests, allowing developers to create dynamic content such as login functionality.

Web application deployment: Tomcat can deploy WAR files by placing them in the webapps directory, automatically extracting and starting them.

Web Server Functionality

HTTP/HTTPS service: Tomcat listens on ports (default 8080) and serves HTTP/HTTPS requests.

Static resource service: Tomcat serves static files like HTML, CSS, JavaScript, and images.

Development and Testing

Development environment support: Tomcat provides hot deployment, allowing changes to be reflected without restart.

IDE integration: Tomcat integrates with IDEs such as Eclipse and IntelliJ IDEA for deployment and debugging.

Installation and Deployment of Tomcat

Environment Information

Before installing Tomcat, install JDK 8. Use OpenJDK from https://jdk.java.net/java-se-ri/8-MR6.

mkdir -p /app/tools && cd /app/tools
wget https://download.java.net/openjdk/jdk8u44/ri/openjdk-8u44-linux-x64.tar.gz
tar -xf openjdk-8u44-linux-x64.tar.gz
ln -s /app/tools/java-se-8u44-ri/ /app/tools/jdk
echo "export JAVA_HOME=/app/tools/jdk" >> /etc/profile
echo "export PATH=$JAVA_HOME/bin:$PATH" >> /etc/profile
source /etc/profile
java -version

Install Tomcat

Download Tomcat 9.0.50 from the Apache archive.

wget https://archive.apache.org/dist/tomcat/tomcat-9/v9.0.50/bin/apache-tomcat-9.0.50.tar.gz
tar -xf apache-tomcat-9.0.50.tar.gz
ln -s $(pwd)/apache-tomcat-9.0.50 tomcat

Start Tomcat

cd tomcat/bin
./startup.sh
# Verify process and port
ps -ef | grep java
ss -lntup | grep 8080

Open http://10.0.0.21:8080 in a browser to confirm Tomcat is running.

Tomcat Directory Structure

Tomcat contains several directories, each serving a specific purpose.

bin directory

The bin directory holds executable scripts such as startup.sh, shutdown.sh, catalina.sh, etc.

conf directory

The conf directory stores configuration files. server.xml – configures HTTP/HTTPS ports and other server settings. web.xml – auxiliary configuration file.

server.xml details

<?xml version="1.0" encoding="UTF-8"?>
<!-- 8005 shutdown port -->
<Server port="8005" shutdown="SHUTDOWN">
    ...
    <Connector port="8080" protocol="HTTP/1.1" connectionTimeout="20000" redirectPort="8443"/>
    <Engine name="Catalina" defaultHost="localhost">
        ...
    </Engine>
</Server>

Log format

%h – client IP address

%l – remote logical username

%u – remote user

%t – access time

%r – request line

%s – HTTP status code

%b – bytes sent

" – double quote

logs directory

Stores Tomcat logs such as catalina.out, daily rotated catalina.YYYY-MM-DD.log, and access logs.

webapps directory

Contains deployed web applications. The ROOT directory is the default web app.

Case: Deploy zrlog Application

Download the zrlog WAR file and deploy it as ROOT.war.

mkdir -p /app/war && cd /app/war
wget https://dl.zrlog.com/release/zrlog.war
mv /app/tools/tomcat/tomcat/webapps /app/tools/tomcat/tomcat/webapps_bak_$(date +%Y%m%d)
mkdir -p /app/tools/tomcat/tomcat/webapps
mv zrlog.war /app/tools/tomcat/tomcat/webapps/ROOT.war

Access the application at http://10.0.0.21:8080.

Create a MySQL container for the database.

docker run -d --name mysql_5.7 -p 3306:3306 --restart always -v /data/mysql:/var/lib/mysql -e MYSQL_ROOT_PASSWORD=1 mysql:5.7
docker exec -it mysql_5.7 mysql -uroot -p1 -e "create database zrlog;"

Configure the database connection in zrlog and complete the setup.

Tomcat Multi-Instance Deployment

Background

When a server has ample resources, multiple Tomcat instances can be deployed to utilize the hardware efficiently.

Deployment Steps

Prepare multiple Tomcat directories

tar -xf apache-tomcat-9.0.50.tar.gz
cp -r apache-tomcat-9.0.50 tomcat_8081
cp -r apache-tomcat-9.0.50 tomcat_8082

Modify ports

# For tomcat_8081
sed -i 's#8005#8006#g' tomcat_8081/conf/server.xml
sed -i 's#8080#8081#g' tomcat_8081/conf/server.xml
sed -i 's#8443#8444#g' tomcat_8081/conf/server.xml
# For tomcat_8082
sed -i 's#8006#8007#g' tomcat_8082/conf/server.xml
sed -i 's#8081#8082#g' tomcat_8082/conf/server.xml
sed -i 's#8444#8445#g' tomcat_8082/conf/server.xml

Start instances

./tomcat_8081/bin/startup.sh
./tomcat_8082/bin/startup.sh

Verify

ss -lntup | grep 8081
ss -lntup | grep 8082

Access the instances at http://10.0.0.21:8081 and http://10.0.0.21:8082.