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March 03, 2025 00:42
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Apache Tomcat Cheatsheet

A quick reference guide to Apache Tomcat, covering essential configurations, deployment, management, and troubleshooting tips for Java web application servers.

Core Configuration

Server.xml Essentials

<Server>: Root element, defines the entire Tomcat server.

  • port: Shutdown port (e.g., 8005).
  • shutdown: Shutdown command (e.g., SHUTDOWN).

Example:

<Server port="8005" shutdown="SHUTDOWN">

<Service>: Contains one or more Connectors and a single Engine.

Example:

<Service name="Catalina">

<Connector>: Defines a port for incoming requests.

  • port: Port number (e.g., 8080, 8443).
  • protocol: Protocol (e.g., HTTP/1.1, org.apache.coyote.http11.Http11NioProtocol).
  • connectionTimeout: Timeout in milliseconds.
  • redirectPort: Port to redirect to for SSL (e.g., 8443).

Example:

<Connector port="8080" protocol="HTTP/1.1"
           connectionTimeout="20000"
           redirectPort="8443" />

<Engine>: Represents the Servlet engine.

  • name: Engine name (e.g., Catalina).
  • defaultHost: Default virtual host.

Example:

<Engine name="Catalina" defaultHost="localhost">

<Host>: Represents a virtual host.

  • name: Hostname (e.g., localhost, example.com).
  • appBase: Application base directory (e.g., webapps).
  • unpackWARs: Unpack WAR files on deploy (true/false).
  • autoDeploy: Automatically deploy web applications (true/false).

Example:

<Host name="localhost"  appBase="webapps"
      unpackWARs="true" autoDeploy="true">

<Context>: Represents a web application.

  • path: Context path (e.g., /, /myapp).
  • docBase: Document base directory or WAR file path.
  • reloadable: Enable auto-reloading on changes (true/false - use with caution in production!).

Example:

<Context path="/myapp" docBase="myapp" reloadable="false"/>

Context Configuration

Context configuration can be defined in server.xml (discouraged for portability) or in individual context XML files under $CATALINA_BASE/conf/Catalina/localhost/.
For example, myapp.xml for a webapp with context path /myapp.

Using context XML files allows for easier deployment and redeployment of web applications without modifying the main server configuration.

Remember to disable auto-deploy and unpackWARs in production environments to avoid unexpected behavior.

Deployment and Management

Web Application Deployment

  1. WAR File Deployment: Copy the WAR file to $CATALINA_BASE/webapps/. Tomcat automatically deploys it.
  1. Exploded WAR Deployment: Copy the exploded WAR directory to $CATALINA_BASE/webapps/.
  1. Context XML Deployment: Create a context XML file in $CATALINA_BASE/conf/Catalina/localhost/ (e.g., myapp.xml) and specify the docBase.

Tomcat Manager Application

Access:

Access the Tomcat Manager application at http://<host>:<port>/manager/html.
Requires authentication configured in $CATALINA_HOME/conf/tomcat-users.xml.

Functions:

Deploy, undeploy, start, stop, and reload web applications. View server status and diagnostics.

Command-Line Management

shutdown.sh / shutdown.bat

Shuts down the Tomcat server.

startup.sh / startup.bat

Starts the Tomcat server.

Security and SSL Configuration

SSL Configuration

  1. Keystore Creation: Use keytool to create a keystore file.

    keytool -genkey -alias tomcat -keyalg RSA -keystore keystore.jks

  1. Connector Configuration: Configure an SSL Connector in server.xml.

    <Connector port="8443" protocol="org.apache.coyote.http11.Http11NioProtocol"
           maxThreads="200" scheme="https" secure="true"
           SSLEnabled="true" keystoreFile="${catalina.home}/conf/keystore.jks"
           keystorePass="changeit" clientAuth="false" sslProtocol="TLS"/>

Key Attributes:

  • keystoreFile: Path to the keystore file.
  • keystorePass: Keystore password.
  • clientAuth: Whether client authentication is required (true/false).
  • sslProtocol: SSL/TLS protocol.

Security Realms

Tomcat supports various security realms for authentication and authorization.
Common realms include:

  • UserDatabaseRealm: Uses the tomcat-users.xml file.
  • JDBCRealm: Uses a JDBC connection to authenticate against a database.
  • JNDIRealm: Uses JNDI to retrieve user information.

Troubleshooting

Common Issues

Port Conflicts: Ensure Tomcat ports (8080, 8005, 8443) are not in use by other applications.

Solution: Change the port numbers in server.xml.

OutOfMemoryError: Tomcat runs out of memory.

Solution: Increase the JVM heap size in CATALINA_OPTS or JAVA_OPTS environment variables.

export CATALINA_OPTS="-Xms512m -Xmx2048m"

Web Application Deployment Failures: Issues during WAR deployment.

Solution: Check Tomcat logs for error messages. Verify the WAR file is valid and the context path is not conflicting with existing applications.

Log Files

  • catalina.out: General Tomcat output, including startup and shutdown messages.
  • localhost_access_log.txt: Access logs for the localhost virtual host.
  • manager.log: Logs for the Tomcat Manager application.
  • Web application logs: Located in the web application’s logging directory (e.g., using Log4j or SLF4J).

Log files are typically located in the $CATALINA_BASE/logs/ directory.