Use the CUBA project tree > Project > Deployment > WAR Settings dialog in Studio or just manually add the buildWar task to the end of build.gradle. You can specify a separate war-context.xml project file to specify connection settings to the production database or provide that file later on the server:

task buildWar(type: CubaWarBuilding) {
    singleWar = true
    includeContextXml = true
    includeJdbcDriver = true
    appProperties = ['cuba.automaticDatabaseUpdate': true]
    webXmlPath = 'modules/web/web/WEB-INF/single-war-web.xml'
    coreContextXmlPath = 'modules/core/web/META-INF/war-context.xml'
}

task buildWar(type: CubaWarBuilding) {
    singleWar = false
    includeContextXml = true
    includeJdbcDriver = true
    appProperties = [
        'cuba.automaticDatabaseUpdate': true,
        'cuba.webPort': 9999,
        'cuba.connectionUrlList': 'http://localhost:9999/app-core'
    ]
}

Run the buildWar gradle task. As a result, app.war file (or several files if you build separate WARs) will be generated in the build/distributions directory of your project.

gradlew buildWar

Install Tomcat 9 package:

sudo apt install tomcat9

Copy the generated app.war file to the /var/lib/tomcat9/webapps directory of the server. You can also remove the /var/lib/tomcat9/webapps/ROOT sample webapp folder if it exists.

Create the application home directory, e.g. /opt/app_home and make the Tomcat server user (tomcat) to be the owner of this folder:

sudo mkdir /opt/app_home
sudo chown tomcat:tomcat /opt/app_home

Tomcat 9 service (unlike earlier versions of the Tomcat Debian package) is sandboxed by systemd and has limited write access to the file system. You can read more about this in the /usr/share/doc/tomcat9/README.Debian file. It is necessary to modify systemd configuration to allow Tomcat service write access to the application home folder:

Create configuration file /usr/share/tomcat9/bin/setenv.sh with the following text:

CATALINA_OPTS="$CATALINA_OPTS -Xmx1024m"
CATALINA_OPTS="$CATALINA_OPTS -Dapp.home=/opt/app_home"

CATALINA_OPTS="$CATALINA_OPTS -Djava.security.egd=file:/dev/./urandom"

If you want to provide production database connection properties with a local file on the server, you can create a file in the /var/lib/tomcat9/conf/Catalina/localhost/ folder. The name of the file depends on the WAR file name, e.g. app.xml for single WAR and app-core.xml if separate WAR files are deployed. Copy contents of the context.xml to this file.

With the default configuration all application log messages are appended to the /var/log/syslog system journal. You have two options how to customize logging configuration of the application:

Restart the Tomcat service:

sudo systemctl restart tomcat9

Open http://localhost:8080/app in your web browser.