Version: 9.3.29.v20201019 |

Chapter 14. Java Management Extensions (JMX)
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## Chapter 14. Java Management Extensions (JMX)

The Java Management Extensions (JMX) API is a standard API for managing and monitoring resources such as applications, devices, services, and the Java virtual machine.

Typical uses of the JMX technology include:

- Consulting and changing application configuration
- Accumulating and making available statistics about application behavior
- Notifying of state changes and erroneous conditions

The JMX API includes remote access, so a remote management program can interact with a running application for these purposes.

## Using JMX with Jetty

Jetty JMX integration uses the platform MBean server implementation that Java VM provides. The integration is based on the `ObjectMBean` implementation of `DynamicMBean`. This implementation allows you to wrap an arbitrary POJO in an MBean and annotate it appropriately to expose it via JMX. See Jetty JMX Annotations.

The `MBeanContainer` implementation of the `Container.Listener` interface coordinates creation of MBeans. The Jetty Server and it’s components use a Container to maintain a containment tree of components and to support notification of changes to that tree. The `MBeanContainer` class listens for Container events and creates and destroys MBeans as required to wrap all Jetty components.

You can access the MBeans that Jetty publishes both through built-in Java VM connector via JConsole or JMC, or by registering a remote JMX connector and using a remote JMX agent to monitor Jetty.

### Configuring JMX

This guide describes how to initialize and configure the Jetty JMX integration.

To monitor an application using JMX, perform the following steps:

- Configure the application to instantiate an MBean container.
- Instrument objects to be MBeans.
- Provide access for JMX agents to MBeans.

#### Using JConsole to Access Jetty MBeans

The simplest way to access the MBeans that Jetty publishes is to use the JConsole utility the Java Virtual Machine supplies. See Managing Jetty with JConsole and JMC for instructions on how to configure JVM for use with JConsole or JMC.

To access Jetty MBeans via JConsole or JMC, you must:

- Enable the registration of Jetty MBeans into the platform MBeanServer.
- Enable a `JMXConnectorServer` so that JConsole/JMC can connect and visualize the MBeans.

#### Registering Jetty MBeans

Configuring Jetty JMX integration differs for standalone and embedded Jetty.

##### Standalone Jetty

JMX is not enabled by default in the Jetty distribution. To enable JMX in the Jetty distribution, run the following, where `{$jetty.home}` is the directory where you have the Jetty distribution located (see the documentation for Jetty base vs. home examples):

    $ java -jar {$jetty.home}/start.jar --add-to-start=jmx

Running the above command will append the available configurable elements of the JMX module to the `{$jetty.base}/start.ini` file. If you are managing separate ini files for your modules in the distribution, use `--add-to-start.d=jmx` instead.

If you wish to add remote access for JMX, you will also need to enable the JMX-Remote module:

    $ java -jar {$jetty.home}/start.jar --add-to-start=jmx-remote

##### Embedded Jetty

When running Jetty embedded into an application, create and configure an MBeanContainer instance as follows:

    Server server = new Server();

    // Setup JMX
    MBeanContainer mbContainer=new MBeanContainer(ManagementFactory.getPlatformMBeanServer());
    server.addEventListener(mbContainer);
    server.addBean(mbContainer);

    // Add loggers MBean to server (will be picked up by MBeanContainer above)
    server.addBean(Log.getLog());

Notice that Jetty creates the `MBeanContainer` immediately after creating the Server, and immediately after registering it as an `EventListener` of the Server object (which is also a Container object).

Because logging is initialized prior to the `MBeanContainer` (even before the Server itself), it is necessary to register the logger manually via `server.addBean()` so that the loggers may show up in the JMX tree.

#### Using the Jetty Maven Plugin with JMX

If you are using the Jetty Maven plugin you should copy the `/etc/jetty-jmx.xml` file into your webapp project somewhere, such as `/src/etc,` then add a `<jettyconfig>` element to the plugin `<configuration>`:

    <plugin>
      <groupid>org.eclipse.jetty</groupid>
      <artifactid>jetty-maven-plugin</artifactid>
      <version>9.3.29.v20201019</version>
      <configuration>
        <scanintervalseconds>10</scanintervalseconds>
        <jettyXml>src/etc/jetty-jmx.xml</jettyXml>
      </configuration>
    </plugin>

### Enabling JMXConnectorServer for Remote Access

There are two ways of enabling remote connectivity so that JConsole or JMC can connect to visualize MBeans.

- Use the `com.sun.management.jmxremote` system property on the command line. Unfortunately, this solution does not work well with firewalls and is not flexible.
- Use Jetty’s `ConnectorServer` class. To enable use of this class, uncomment the correspondent portion in `/etc/jetty-jmx.xml,` like this:

    <New id="ConnectorServer" class="org.eclipse.jetty.jmx.ConnectorServer">
      <Arg>
        <New class="javax.management.remote.JMXServiceURL">
          <Arg type="java.lang.String">rmi</Arg>
          <Arg type="java.lang.String" />
          <Arg type="java.lang.Integer"><SystemProperty name="jetty.jmxrmiport" default="1099"/></Arg>
          <Arg type="java.lang.String">/jndi/rmi://<SystemProperty name="jetty.jmxrmihost" default="localhost"/>:<SystemProperty name="jetty.jmxrmiport" default="1099"/>/jmxrmi</Arg>
        </New>
      </Arg>
      <Arg>org.eclipse.jetty.jmx:name=rmiconnectorserver</Arg>
      <Call name="start" />
    </New>

This configuration snippet starts an `RMIRegistry` and a `JMXConnectorServer` both on port 1099 (by default), so that firewalls should open just that one port to allow connections from JConsole or JMC.

### Securing Remote Access

`JMXConnectorServer` several options to restrict access. For a complete guide to controlling authentication and authorization in JMX, see Authentication and Authorization in JMX RMI connectors in Luis-Miguel Alventosa’s blog.

To restrict access to the `JMXConnectorServer`, you can use this configuration, where the `jmx.password` and `jmx.access` files have the format specified in the blog entry above:

    <New id="ConnectorServer" class="org.eclipse.jetty.jmx.ConnectorServer">
      <Arg>
        <New class="javax.management.remote.JMXServiceURL">
          <Arg type="java.lang.String">rmi</Arg>
          <Arg type="java.lang.String" />
          <Arg type="java.lang.Integer"><SystemProperty name="jetty.jmxrmiport" default="1099"/></Arg>
          <Arg type="java.lang.String">/jndi/rmi://<SystemProperty name="jetty.jmxrmihost" default="localhost"/>:<SystemProperty name="jetty.jmxrmiport" default="1099"/>/jmxrmi</Arg>
        </New>
      </Arg>
      <Arg>
        <Map>
          <Entry>
            <Item>jmx.remote.x.password.file</Item>
            <Item>
              <New class="java.lang.String"><Arg><Property name="jetty.home" default="." />/resources/jmx.password</Arg></New>
            </Item>
          </Entry>
          <Entry>
            <Item>jmx.remote.x.access.file</Item>
            <Item>
              <New class="java.lang.String"><Arg><Property name="jetty.home" default="." />/resources/jmx.access</Arg></New>
            </Item>
          </Entry>
        </Map>
      </Arg>
      <Arg>org.eclipse.jetty.jmx:name=rmiconnectorserver</Arg>
      <Call name="start" />
    </New>

### Custom Monitor Application

Using the JMX API, you can also write a custom application to monitor your Jetty server. To allow this application to connect to your Jetty server, you need to uncomment the last section of the `/etc/jetty-jmx.xml` configuration file and optionally modify the endpoint name. Doing so creates a JMX HTTP connector and registers a JMX URL that outputs to the `Stderr` log.

You should provide the URL that appears in the log to your monitor application in order to create an `MBeanServerConnection.` You can use the same URL to connect to your Jetty instance from a remote machine using JConsole or JMC. See the configuration file for more details.

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