Untitled :: Jolokia

Jakarta EE Agent (WAR)

Installation and Configuration

The WAR agent is the most popular variant, and can be deployed in a servlet container just like any other Jakarta EE web application.

Tomcat example

A simple example for deploying the WAR agent on Tomcat can be found in the Jolokia quickstart.

Often, installation is simply a matter of copying the agent WAR to a deployment directory (webapps/ directory on Tomcat). On other platforms an administrative Web GUI or a command line tool need to be used for deployment. Providing detailed installation instructions for every servlet container is out of scope for this document.

The servlet itself can be configured in two ways:

Servlet Init Parameters

Jolokia can be configured with init-param declarations within the servlet definition in WEB-INF/web.xml. The known parameters are described in Table 1, “Servlet init parameters”. The stock agent needs to be repackaged, though, in order to modify the internal web.xml.

Servlet Context Parameters

A more convenient possibility might be to use servlet context parameters, which can be configured outside the WAR archive. This is done differently for each servlet container but involves typically the editing of a configuration file. E.g. for Tomcat 10.1, the context for the Jolokia agent can be adapted by putting a file jolokia.xml below $TC/conf/Catalina/localhost/ with a content like:

<Context>
  <Parameter name="maxDepth" value="1"/>
</Context>

Additionally, the configuration options discoveryEnabled and discoveryAgentUrl can be provided via environment variables or system properties, too. See below for details.

Table 1. Servlet init parameters
Parameter	Description	Example
`jsr160ProxyAllowedTargets`	Path to a white list of patterns which are matched against possible JMX service URL for incoming requests. If no white list is specified, default blacklist is effective which includes `service:jmx:rmi:///jndi/ldap:.*`.	`/opt/jolokia/jsr160-proxy-allowed-patterns.txt`
`policyLocation`	Location of the policy file to use. This is either a URL which can read from (like a `file:` or `http:` URL) or with the special protocol `classpath:` which is used for looking up the policy file in the web application’s classpath. See Policy Location for details about this parameter.	`file:/home/jolokia/jolokia-access.xml` for a file based access to the policy file. Default is `classpath:/jolokia-access.xml`.
`restrictorClass`	Full classname of an implementation of `org.jolokia.server.core.service.api.Restrictor` which is used as a custom restrictor for securing access via Jolokia.	`com.mycompany.jolokia.CustomRestrictor` (which must be included in the war file and must implement `org.jolokia.server.core.service.api.Restrictor`)
`allowDnsReverseLookup`	Access can be restricted based on the remote host accessing Jolokia. This host can be specified as address or an hostname. However, using the hostname normally requires a reverse DNS lookup which might slow down operations. If you want to use reverse DNS lookup set this property to `true`.	Default: `false`
`debug`	Debugging state after startup. Can be changed via the config MBean during runtime.	Default: `false`
`logHandlerClass`	Loghandler to use for providing logging output. By default logging is written to standard out and error but you can provide here a Java class implementing `org.jolokia.server.core.service.api.LogHandler` for an alternative log output. Few implementations are included in WAR this agent: `org.jolokia.server.core.service.impl.StdoutLogHandler` which logs to standard output `org.jolokia.server.core.service.impl.QuietLogHandler` which switches off logging completely. `org.jolokia.server.core.service.impl.JulLogHandler` which uses a `java.util.logging` Logger with name `org.jolokia` `org.jolokia.server.core.http.AgentServlet.ServletLogHandler` is used by default and delegates to `jakarta.servlet.GenericServlet.log()` methods	Default: `org.jolokia.server.core.http.AgentServlet.ServletLogHandler`
`logHandlerName`	A parameter which may be used to configure logger name which may be used with some `org.jolokia.server.core.service.api.LogHandler` implementations.	Default: `org.jolokia`
`historyMaxEntries`	Entries to keep in the history. Can be changed at runtime via the config MBean.	Default: `10`
`debugMaxEntries`	Maximum number of entries to keep in the local debug history (if enabled). Can be changed via the config MBean at runtime.	Default: `100`
`maxDepth`	Maximum depth when traversing bean properties. If set to 0, depth checking is disabled	Default: `15`
`maxCollectionSize`	Maximum size of collections returned when serializing to JSON. When set to 0, collections are never truncated.	Default: `0`
`maxObjects`	Maximum number of objects which are traversed when serializing a single response. Use this as an airbag to avoid boosting your memory and network traffic. Nevertheless, when set to 0 no limit is imposed.	Default: `0`
`mbeanQualifier`	Qualifier to add to the ObjectName of Jolokia’s own MBeans. This can become necessary if more than one agent is active within a servlet container. This qualifier is added to the `ObjectName` of this agent with a comma. For example a `mbeanQualifier` with the value `qualifier=own` will result in Jolokia server handler MBean with the name `jolokia:type=ServerHandler,qualifier=own`
`mimeType`	MIME to use for the JSON responses. Only `application/json` and `text/plain` are allowed. If any other type is given, Jolokia falls back to `text/plain`.	Default: `text/plain`
`canonicalNaming`	This option specifies in which order the key-value properties within ObjectNames as returned by `list` or `search` are returned. By default this is the so called 'canonical order' in which the keys are sorted alphabetically. If this option is set to `false`, then the natural order is used, i.e. the object name as it was registered. This option can be overridden with a query parameter of the same name.	Default: `true`
`includeStackTrace`	Whether to include a stacktrace of an exception in case of an error. By default it it set to `true` in which case the stacktrace is always included. If set to `false`, no stacktrace is included. If the value is `runtime` a stacktrace is only included for RuntimeExceptions. This global option can be overridden with a query parameter.	Default: `false`
`serializeException`	When this parameter is set to `true`, then an exception thrown will be serialized as JSON and included in the response under the key `error_value`. No stacktrace information will be included, though. This global option can be overridden by a query parameter of the same name.	Default: `false`
`allowErrorDetails`	If set to `false` then no error details like a stack trace (when `includeStackTrace` is set) or a serialized exception (when `serializeExceptin` is set) are included. This can be user as a startup option to avoid exposure of error details regardless of other options.	Default: `true`
`detectorOptions`	Extra options passed to a detector after successful detection of an application server. See below for an explanation.
`discoveryEnabled`	If set to `true` then this servlet will listen for multicast request (multicast-group 239.192.48.84, port 24884 by default, but can be changed). By default this option is disabled in order to avoid conflicts with an Jakarta EE standards (though this should’t harm anyways). This option can also be switched on with an environment variable `JOLOKIA_DISCOVERY_ENABLED` or the system property `jolokia.discoveryEnabled` set to `true`.	Default: `false`
`discoveryAgentUrl`	Sets the URL to respond for multicast discovery requests. If given, `discoveryEnabled` is set implicitly to `true`. This URL can also be provided by an environment variable `JOLOKIA_DISCOVERY_AGENT_URL` or the system property `jolokia.discoveryAgentUrl`. Within the value you can use the placeholders `${host}` and `${ip}` which gets replaced by the autodetected local host name/address. Also with `${env:ENV_VAR}` and `${sys:property}` environment and system properties can be referenced, respectively.	`http://10.9.11.87:8080/jolokia`
`multicastGroup`	The multicast group IPv4 address. This group IP can be also given as an environment variable `JOLOKIA_MULTICAST_GROUP` or a system property `jolokia.multicastGroup`	Default: `239.192.48.84`
`multicastPort`	The multicast port. This port can be also given as an environment variable `JOLOKIA_MULTICAST_PORT` or a system property `jolokia.multicastPort`	Default: `24884`
`agentId`	A unique ID for this agent. By default a unique id is calculated. If provided it should be ensured that this id is unique among all agent reachable via multicast requests used by the discovery mechanism. It is recommended not to set this value. Within the `agentId` specification you can use the same placeholders as in `discoveryAgentUrl`.	`my-unique-agent-id`
`agentDescription`	An optional description which can be used for clients to present a human readable label for this agent.	`Monitoring agent`

Jolokia has various detectors which can detect the brand and version of an application server it is running in. This version is revealed with the version command. With the configuration parameter detectorOptions extra options can be passed to the detectors. These options take the form of a JSON object, where the keys are productnames and the values other JSON objects containing the specific configuration. This configuration is feed to a successful detector which can do some extra initialization on agent startup. Currently the following extra options are supported:

Table 2. Detector Options
Product	Option	Description
glassfish	bootAmx	If `false` and the agent is running on GlassFish, this will cause the AMX subsystem not to be booted during startup. By default, AMX which contains all relevant MBeans for monitoring GlassFish is booted.

Security Setup

The WAR agent comes in two flavors:

jolokia-agent-war.war: The standard agent which is secured with the role jolokia. You have to setup your servlet container to connect this role to the authentication.
jolokia-agent-war-unsecured.war: A demo agent, which is completely unsecured. Please use this agent only for evaluation purposes, but it is highly recommended that use the security enabled agent jolokia.war.

Jakarta EE security is enabled by default by adding the required information within the web.xml.

Using jmx4perl’s jolokia tool

jmx4perl comes with a nice command line utility called jolokia which allows for an easy setup of security within a given jolokia.war.

All current client libraries are able to use BASIC HTTP authentication with user and password. The <login-config> should be set accordingly. The <security-constraint> specifies the URL pattern (which is in the default setup specify all resources provided by the Jolokia servlet) and a role name jolokia which is used to find the proper authentication credentials. This role must be referenced outside the agent WAR within the servlet container, e.g. for Tomcat the role definition can be found in $TOMCAT/config/tomcat-users.xml.

Programmatic usage of the Jolokia agent servlet

The Jolokia agent servlet can be integrated into one’s own web applications as well. Simply add a servlet with the servlet class org.jolokia.server.core.http.AgentServlet to your own web.xml. The following example maps the agent to the context /jolokia:

<servlet>
  <servlet-name>jolokia-agent</servlet-name>
  <servlet-class>org.jolokia.server.core.http.AgentServlet</servlet-class>
  <load-on-startup>1</load-on-startup>
</servlet>

<servlet-mapping>
  <servlet-name>jolokia-agent</servlet-name>
  <url-pattern>/jolokia/*</url-pattern>
</servlet-mapping>

Of course, any init parameter as described in Table 1, “Servlet init parameters” can be used here as well.

In order for this servlet definition to find the referenced Java class, the JAR jolokia-server-core.jar must be included. Maven users can declare a dependency on this jar artifact:

<project>
  <!-- ....  -->
  <dependencies>
    <dependency>
      <groupId>org.jolokia</groupId>
      <artifactId>jolokia-server-core</artifactId>
      <version>2.0.2</version>
    </dependency>
  </dependencies>
  <!-- .... -->
</project>

The org.jolokia.server.core.http.AgentServlet can be subclassed, too in order to provide a custom restrictor or a custom log handler. See Jolokia Restrictors for details.

Also, multiple Jolokia agents can be deployed in the same JVM without problem. However, since the agent deploys some Jolokia-specific MBeans on the single PlatformMBeansServer, for multi-agent deployments it is important to use the mbeanQualifier init parameter to distinguish multiple Jolokia MBeans by adding an extra property to those MBeans' names. This also needs to be done if multiple webapps containing Jolokia agents are deployed on the same Jakarta EE server.