Install the Apache Tomcat on Ubuntu Linux

Apache Tomcat is an open-source implementation of the Java Servlet, JavaServer Pages, Java Expression Language and WebSocket technologies.
Tomcat provides a "pure Java" HTTP web server environment in which Java code can run.

First you need to install Java --> Install Java with apt on Ubuntu Linux

Install Tomcat

Create Tomcat directory

sudo mkdir /opt/tomcat

Navigate to opt directory

cd /opt/

Download Tomcat

wget https://downloads.apache.org/tomcat/tomcat-9/v9.0.36/bin/apache-tomcat-9.0.36.tar.gz

Extract the archive in Tomcat directory

sudo tar xzvf apache-tomcat-9*tar.gz -C /opt/tomcat --strip-components=1

Change all files in bin folder permissions

sudo chmod -R 755 /opt/tomcat/bin

Create a systemd Service File

Find JAVA_HOME

java -XshowSettings:properties -version 2>&1 > /dev/null | grep 'java.home'

Output:

java.home = /usr/lib/jvm/java-8-openjdk-amd64/jre

Create the systemd service file for Tomcat

sudo nano /etc/systemd/system/tomcat.service

Paste the following contents into your service file. Modify the value of JAVA_HOME if necessary to match the value you found on your system. You may also want to modify the memory allocation settings that are specified in CATALINA_OPTS:

[Unit]
Description=Apache Tomcat Web Application Container
After=network.target

[Service]
Type=forking

Environment=JAVA_HOME=/usr/lib/jvm/java-8-openjdk-amd64/jre
Environment=CATALINA_PID=/opt/tomcat/temp/tomcat.pid
Environment=CATALINA_HOME=/opt/tomcat
Environment=CATALINA_BASE=/opt/tomcat
Environment='CATALINA_OPTS=-Xms512M -Xmx1024M -server -XX:+UseParallelGC'
Environment='JAVA_OPTS=-Djava.awt.headless=true -Djava.security.egd=file:/dev/./urandom'

ExecStart=/opt/tomcat/bin/startup.sh
ExecStop=/opt/tomcat/bin/shutdown.sh

User=root
Group=root
UMask=0007
RestartSec=10
Restart=always

[Install]
WantedBy=multi-user.target

When you are finished, save and close the file.

Reload the systemd daemon so that it knows about our service file

sudo systemctl daemon-reload

Start the Tomcat service

sudo systemctl start tomcat

Double check that it started without errors

sudo systemctl status tomcat | cat

Adjust the Firewall and Test the Tomcat Server

Tomcat uses port 8080 to accept conventional requests. Allow traffic to that port

sudo ufw allow 8080

If you were able to successfully accessed Tomcat, now is a good time to enable the service file so that Tomcat automatically starts at boot

sudo systemctl enable tomcat

Configure Tomcat Web Management Interface

In order to use the manager web app that comes with Tomcat, we must add a login to our Tomcat server.
We will do this by editing the tomcat-users.xml file:

sudo nano /opt/tomcat/conf/tomcat-users.xml

You will want to add a user who can access the manager-gui and admin-gui (web apps that come with Tomcat). You can do so by defining a user, similar to the example below, between the tomcat-users tags.
Be sure to change the username and password to something secure:

<user username="barrouh" password="password@@" roles="manager-gui,admin-gui"/>

Save and close the file when you are finished.

By default, newer versions of Tomcat restrict access to the Manager and Host Manager apps to connections coming from the server itself. Since we are installing on a remote machine, you will probably want to remove or alter this restriction. To change the IP address restrictions on these, open the appropriate context.xml files.

For the Manager app, type:

sudo nano /opt/tomcat/webapps/manager/META-INF/context.xml

For the Host Manager app, type:

sudo nano /opt/tomcat/webapps/host-manager/META-INF/context.xml

Inside, comment out the IP address restriction to allow connections from anywhere. Alternatively, if you would like to allow access only to connections coming from your own IP address, you can add your public IP address to the list:
context.xml files for Tomcat webapps

<Context antiResourceLocking="false" privileged="true" >
  <!--<Valve className="org.apache.catalina.valves.RemoteAddrValve"
         allow="127\.\d+\.\d+\.\d+|::1|0:0:0:0:0:0:0:1" />-->
</Context>

Save and close the files when you are finished.

To put our changes into effect, restart the Tomcat service:

sudo systemctl restart tomcat