Welcome to this hands-on lab, where you will be setting up an Apache web server as a load balancer front end to Apache Tomcat. This will also provide fail over capabilities which will be tested.
Apache’s Tomcat is a Java-based application platform built around deploying and managing Java Web Applications. The Apache web server is an application that powers many of the world’s web sites.
This hands-on lab focuses on installing and configuring the Apache web server as a load balancer/failover cluster with sticky sessions to two pre-installed instances of Tomcat.
The servers provided are running Red Hat Enterprise 8. Tomcat 9 is pre-installed on two of the servers, and available on port **8080**. You will be tasked with making Tomcat available on port **80** on the load balancer, with failover working via the Apache httpd server.
Once you have completed the task, you will need to ensure you can connect via port **80** and access the Tomcat GUI. You should check which Tomcat instance is being shown, and make sure the failover works by shutting down that instance and testing again to see that you are viewing the second instance.
Learning Objectives
Successfully complete this lab by achieving the following learning objectives:
- Test to Ensure You Can Access the Preconfigured Tomcat Instances on Port 8080
You will have three servers. The second and third are the Tomcat servers. It may take from 3 to 10 minutes after the hands-on lab has started before you can access them. When enough time has elapsed, visit those two servers’ public IP addresses on port 8080 in a web browser.
To access them, copy the external IP addresses and test in your browser by using the IP address and appending :8080 to it.
For example, if an IP address shown was 3.92.152.3, then you would put the following into your web browser:
http://3.92.152.3:8080
You should see a Tomcat GUI at each server’s public IP.
- Install the Apache Web Server onto the First Provided Lab Server and Configure It as a Load Balancer to the Two Tomcat Instances
Log into the load balancer (via SSH) and install the Apache web server:
sudo dnf install httpd sudo systemctl enable httpd sudo systemctl start httpdGo to a browser and test that the Apache web server is working by connecting to its IP address. You should see the default Apache web page. Now you need to configure the load balancer.
Edit the Apache web server’s configuration file. This can be found at
/etc/httpd/conf/httpd.conf. If you used Vim, the command would be as follows.sudo vim /etc/httpd/conf/httpd.confJump to the end of the file, and edit above where it has the following entry:
IncludeOptional conf.d/*.confYou can use the following as an example of what needs to be inside this configuration file (Note: Replace the
TOMCAT1-INTERNAL-IPandTOMCAT2-INTERNAL-IPwith the respective internal IP address of each Tomcat server):LoadModule proxy_module modules/mod_proxy.so LoadModule proxy_balancer_module modules/mod_proxy_balancer.so LoadModule proxy_http_module modules/mod_proxy_http.so <IfModule proxy_module> ProxyRequests on ProxyPass /examples balancer://mycluster stickysession=JSESSIONID ProxyPassReverse /examples balancer://mycluster stickysession=JSESSIONID <Proxy balancer://mycluster> BalancerMember http://TOMCAT1-INTERNAL-IP:8080/examples route=tomcat1 BalancerMember http://TOMCAT2-INTERNAL-IP:8080/examples route=tomcat2 </Proxy> </IfModule>- Make Changes to the Tomcat Instances as Required, by Editing Configuration in Each’s /usr/local/tomcat9 Directory
Log into one Tomcat server with SSH, not the Tomcat GUI. Edit
server.xmlto make the required changes:sudo vim /usr/local/tomcat9/conf/server.xmlChange this line:
<Engine name="Catalina" defaultHost="localhost" >Make it read:
<Engine name="Catalina" defaultHost="localhost" jvmRoute="tomcat1">Save and exit, then restart Tomcat.
systemctl restart tomcatNow log into the second Tomcat server, again with SSH (not the Tomcat GUI). Edit
server.xmlto make the required changes:sudo vim /usr/local/tomcat9/conf/server.xmlChange this line:
<Engine name="Catalina" defaultHost="localhost" >Make it read:
<Engine name="Catalina" defaultHost="localhost" jvmRoute="tomcat2">Save and exit, then restart Tomcat:
systemctl restart tomcat- Either Disable or Change SELinux so That the Load Balancing Will Work
SELinux is enabled on the hands-on lab server. You can choose to disable it, or adjust it so it allows the Apache web server to act as a load balancer. Both ways are shown here:
Disabling SELinux
To Disable SELinux you would do the following:
sudo setenforce permissiveThen edit the SELinux config file to change the server to be permissive.
sudo vim /etc/selinux/configOnce in the editor, edit this line:
SELINUX=enforcingChange
enforcingtopermissive, so that it looks like this:SELINUX=permissiveSave the file, then use the
setenforcecommand to change the running SELinux to be permissive.sudo setenforce permissiveEditing SELinux
If you wish to keep SELinux enabled, and allow it to permit Apache web server to work as a proxy, you would run the following commands:
sudo setsebool -P httpd_can_network_connect 1 sudo setsebool -P httpd_can_network_relay 1 sudo setsebool -P httpd_graceful_shutdown 1 sudo setsebool -P nis_enabled 1- Restart the Apache Web Server and Confirm You Can Access the Test Application, Then Test to Ensure the Failover Works
Restart the Apache web server and check for errors. If there are errors and Apache does not start, then troubleshoot those errors:
sudo systemctl restart httpdYou can test to see if the load balancer is working by going to the web page of the Apache web server. Then go to the URL that will be serving the load balanced application. That URL will be:
http://LOAD-BALANCER-IP/examples/servlets/servlet/SessionExample
If your Apache server’s external IP address was 18.144.72.70, for example, you would go to this URL:
http://18.144.72.70/examples/servlets/servlet/SessionExample
Change the above IP address to be your own.
You should be able to see a web page that shows something like the following. It will be slightly different in your own example:
Sessions Example Session ID: 71DA102F3D1AF0818230595F801A93B7.tomcat1If you see something like this then it works.
The previous task displayed a Session ID: that showed which Tomcat server you were connected to. Confirm the failover works by shutting down that Tomcat server (in the terminal you already have a session open in):
sudo systemctl stop tomcatThen refresh your load balancer web page. You should now get connected to the second Tomcat server, and the application should show the other Tomcat server’s Session ID.
If this did not happen, but you still see the page, check to make sure you shutdown the correct Tomcat server. If you see an error page or not found, there is a problem and you will need to troubleshoot it.
