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Debian上Tomcat如何进行集群部署

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导读：Prerequisites Before configuring the Tomcat cluster on Debian, ensure the following prerequisites are met: All Debian s...

Prerequisites
Before configuring the Tomcat cluster on Debian, ensure the following prerequisites are met:

  • All Debian servers in the cluster have the same Tomcat version installed (e.g., Tomcat 9).
  • Java Development Kit (JDK) 8 or later is installed (sudo apt install default-jdk).
  • A dedicated system user (e.g., tomcat) is created for running Tomcat instances to enhance security (sudo groupadd tomcat & & sudo useradd -s /bin/false -g tomcat -d /opt/tomcat tomcat).
  • Network connectivity between all cluster nodes (for multicast communication, which is the default clustering method).

Step 1: Install Tomcat on Each Node

  1. Update the package list and install Tomcat:
    sudo apt update &
    &
     sudo apt install tomcat9 tomcat9-admin
  2. Verify the installation by accessing http://< node-ip> :8080 in a browser. You should see the Tomcat welcome page.

Step 2: Configure Multiple Tomcat Instances
To run multiple Tomcat instances on a single node (or across multiple nodes), duplicate the Tomcat directory and customize ports for each instance:

  1. Create instance directories (e.g., tomcat1, tomcat2):
    sudo mkdir -p /opt/tomcat1/{
conf,webapps,temp,work}
     &
    &
 sudo cp -R /usr/share/tomcat9/* /opt/tomcat1/
sudo mkdir -p /opt/tomcat2/{
conf,webapps,temp,work}
     &
    &
     sudo cp -R /usr/share/tomcat9/* /opt/tomcat2/
  2. Modify ports in each instance’s conf/server.xml to avoid conflicts:
    • Shutdown Port: Change < Connector port="8005" to unique values (e.g., 8005 for tomcat1, 8006 for tomcat2).
    • HTTP Connector: Change < Connector port="8080" to unique values (e.g., 8081 for tomcat2).
    • AJP Connector: Change < Connector port="8009" to unique values (e.g., 8010 for tomcat2).
  3. Set ownership of instance directories to the tomcat user:
    sudo chown -R tomcat:tomcat /opt/tomcat1 /opt/tomcat2

Step 3: Enable Clustering in server.xml
Edit the conf/server.xml file for each Tomcat instance to enable clustering. The key configurations include:

  • Cluster Class: Use org.apache.catalina.ha.tcp.SimpleTcpCluster for basic TCP clustering.
  • Membership: Configure multicast communication (all nodes must use the same multicast address and port).
  • JvmRoute: Add a unique jvmRoute attribute to the < Engine> element (e.g., jvmRoute="node1" for tomcat1, jvmRoute="node2" for tomcat2).

Example configuration for one node:

<
    Engine name="Catalina" defaultHost="localhost" jvmRoute="node1">
    
    <
    Cluster className="org.apache.catalina.ha.tcp.SimpleTcpCluster">
    
        <
    !-- Membership: Multicast for cluster discovery -->
    
        <
    Channel className="org.apache.catalina.tribes.group.GroupChannel">
    
            <
    Membership className="org.apache.catalina.tribes.membership.McastService"
                       address="228.0.0.4" 
                       port="45564" 
                       frequency="500" 
                       dropTime="3000"/>
    
            <
    !-- Receiver: TCP listener for this node -->
    
            <
    Receiver className="org.apache.catalina.tribes.transport.nio.NioReceiver"
                      address="auto" 
                      port="4000" 
                      autoBind="100" 
                      selectorTimeout="5000"/>
    
            <
    !-- Sender: Replication transmitter -->
    
            <
    Sender className="org.apache.catalina.tribes.transport.ReplicationTransmitter">
    
                <
    Transport className="org.apache.catalina.tribes.transport.nio.PooledParallelSender"/>
    
            <
    /Sender>
    
            <
    !-- Interceptors: Failure detection and message dispatch -->
    
            <
    Interceptor className="org.apache.catalina.tribes.group.interceptors.TcpFailureDetector"/>
    
            <
    Interceptor className="org.apache.catalina.tribes.group.interceptors.MessageDispatchInterceptor"/>
    
        <
    /Channel>
    
        <
    !-- Replication Valve: Filters non-session resources -->
    
        <
    Valve className="org.apache.catalina.ha.tcp.ReplicationValve" 
               filter=".*\.gif;
    .*\.js;
    .*\.jpg;
    .*\.png;
    .*\.css;
    .*\.txt"/>
    
        <
    !-- Session Listener: Tracks session changes -->
    
        <
    ClusterListener className="org.apache.catalina.ha.session.ClusterSessionListener"/>
    
    <
    /Cluster>
    
<
    /Engine>

Repeat this step for all nodes, ensuring the jvmRoute and Receiver port are unique per instance.

Step 4: Configure Session Replication
For session consistency across the cluster, add the < distributable/> element to the web.xml file of each web application:

<
    web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee" 
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee 
                             http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd" 
         version="4.0">
    
    <
    distributable/>
    
<
    /web-app>

This tells Tomcat to replicate sessions across the cluster.

Step 5: Set Up a Load Balancer (Nginx)
Use Nginx as a reverse proxy to distribute requests across the Tomcat cluster. Install Nginx and configure it as follows:

  1. Install Nginx:
    sudo apt install nginx
  2. Edit the Nginx configuration file (e.g., /etc/nginx/sites-available/default):
    upstream tomcat_cluster {
    
    server 192.168.1.101:8080;
      # Replace with IP/port of tomcat1
    server 192.168.1.102:8081;
  # Replace with IP/port of tomcat2
}


server {
    
    listen 80;
    
    server_name your_domain.com;


    location / {
    
        proxy_pass http://tomcat_cluster;
    
        proxy_set_header Host $host;
    
        proxy_set_header X-Real-IP $remote_addr;
    
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    
        proxy_set_header X-Forwarded-Proto $scheme;

    }

}
  3. Restart Nginx to apply changes:
    sudo systemctl restart nginx

Step 6: Start and Validate the Cluster

  1. Start each Tomcat instance as the tomcat user:
    sudo systemctl start tomcat9@tomcat1  # For instance 1
sudo systemctl start tomcat9@tomcat2  # For instance 2
  2. Check cluster status by accessing the Tomcat Manager (e.g., http://< node-ip> :8080/manager/html) and navigating to the “Cluster” section. You should see all nodes listed as “running.”
  3. Test session replication by deploying a sample application (e.g., a simple JSP with a session variable) to the cluster. Access the app through Nginx and verify that the session persists across different Tomcat instances.

Optional: Use Redis for Centralized Session Storage
For more robust session management (e.g., across multiple data centers), configure Tomcat to use Redis as a session store:

  1. Install Redis:
    sudo apt install redis-server
  2. Add the Redis session manager dependency to your web application’s WEB-INF/lib directory (e.g., tomcat-redis-session-manager-x.x.x.jar and commons-pool2-x.x.x.jar).
  3. Configure the context.xml file of your web application:
    <
    Context>
    
    <
    Manager className="org.apache.catalina.session.PersistentManager"
             storeClassName="org.apache.catalina.session.RedisStore"
             connectionURL="redis://localhost:6379/0"
             driverName="org.apache.tomcat.session.RedisStore"/>
    
<
    /Context>

This setup ensures sessions are stored in Redis, eliminating the need for multicast communication.

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