Untitled :: Jolokia

JVM Agent

The JVM agent is the right agent when it comes to instrument an arbitrary Java application which is not covered by the other agents. This agent can be started by any Java program by providing certain startup options to the JVM. Or it can be dynamically attached (and detached) to an already running Java process. This universal agent uses the JVM Attach API or Java Instrument API and is available for every JVM 1.6 and later.

Dynamic loading of agents will be removed at some point. See JEP 451 for details.

Jolokia as JVM Agent

The JVM agent uses the Java Instrument API for linking into any JVM at startup time. Under the hood it uses an HTTP-Server, which is available on every Oracle/Sun JVM from version 1.6 upwards.

The JDK embedded HTTP-Server is not the fastest one (it is used e.g. for the JAXWS reference implementation), but for our monitoring needs the performance is sufficient. There are several configuration options for tuning the HTTP server’s performance. See below for details.

Installation

This agent gets installed by providing a single startup option -javaagent when starting the Java process.

java -javaagent:/path/to/agent.jar=port=7777,host=localhost

agent.jar is the filename of the Jolokia JVM agent. The agent can be downloaded like the others from the download page. When downloading from a Maven repository you need to check for the classifier javaagent (i.e. the jar to download looks like jolokia-agent-jvm-2.0.2-javaagent.jar, not jolokia-agent-jvm-2.0.2.jar). Options can be appended as a comma separated list. The available options are the same as described in Servlet init parameters plus the one described in table Table 1, “JVM agent configuration options”. If an option contains a comma, an equal sign or a backslash, it must be escaped with a backslash.

Table 1. JVM agent configuration options
Parameter	Description	Example
`agentContext`	Context under which the agent is deployed. The full URL will be `protocol://host:port/agentContext`. The default context is `/jolokia`.	`/j4p`
`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.	`Intranet Timebooking Server`
`host`	Hostaddress to which the HTTP server should bind to. If "*" or "0.0.0.0" is given, the servers binds to every network interface.	`localhost`
`port`	Port the HTTP server should listen to. If set to 0, then an arbitrary free port will be selected.	`8778`
`user`	User to be used for authentication (along with a `password`)
`password`	Password used for authentication (`user` is then required, too)
`realm`	Sets the security realm to use. If the `authMode` is set to `jaas` this is also used as value for the security domain. E.g. for Karaf 3 and later, this realm should be `karaf` since all JMX MBeans are guarded by this security domain.	`jolokia`
`authMode`	Can be either `basic` (the default), `jaas` or `delegate`. If `jaas` is used, the user and password given in the `Authorization:` header are used for login in via JAAS and, if successful, the return subject is used for all Jolokia operation. This has only an effect, if user is set. For authentication mode `delegate`, the authentication decision is delegated to a service specified by `authUrl` (see below for details).	`basic`
`authMatch`	If MultiAuthenticator is used, this config item explains how to combine multiple authenticators. Supported values: `any` at least one authenticator must match, `all` all authenticators must match.	`any`
`authClass`	Fully qualified name of an authenticator class. Class must be on classpath and must extend `com.sun.net.httpserver.Authenticator`. Class can declare a constructor that takes one argument of a type `org.jolokia.server.core.config.Configuration` in which case Jolokia runtime configuration will be passed (useful in cases where authenticator requires additional configuration). If no such constructor is found, default (no-arg) constructor will be use to create an instance.
`authUrl`	URL of a service used for checking the authentication. This configuration option is only effective if `authMode` is set to `delegate`. This URL can have a HTTP or HTTPS scheme. The initially provided `Authorization:` header is copied over to the request against this URL.
`authPrincipalSpec`	Expression used for extracting a principal name from the response of a delegate authentication service. This parameter is only in use when the `authMode` is set to `delegate`. The following expressions are supported: `json:path` a path into a JSON response which points to the principal. E.g. a principal spec `jason:metadata/name` will select the "name" property within the JSON object specified by the "metadata" property. For navigate into arrays, numeric indexes can be used. `empty:` Always extracts an empty (`""`) principal. If this option is not specified, not principal is extracted.
`authIgnoreCerts`	If given, the `authMode` is set to `delegate` and the delegate URL is as HTTPS-URL then the server certificate as well as the server’s DNS name will not be verified. This useful in order to avoid (or introduce) complex keymanagement issues, but is of course less secure. By default certs a verified with the local keystore.
`protocol`	HTTP protocol to use. Should be either `http` or `https`. For the SSL stack there are various additional configuration options.	`http`
`backlog`	Size of request backlog before requests get discarded.	`10`
`executor`	Threading model of the HTTP server: `fixed` Thread pool with a fixed number of threads (see also `threadNr`) `cached` Cached thread pool which creates threads on demand `single` A single thread only	`single`
`threadNamePrefix`	Thread name prefix that executor will use while creating new thread(s).	`jolokia-`
`threadNr`	Number of threads to be used when the `fixed` execution model is chosen.	`5`
`keystore`	Path to the SSL keystore to use (https only)
`keystorePassword`	Keystore password (https only). If the password is given embedded in brackets `[[...]]`, then it is treated as an encrypted password which was encrypted with `java -jar jvm-agent.jar encrypt`. See below for details.
`useSslClientAuthentication`	Whether client certificates should be used for authentication. The presented certificate is validated that it is signed by a known CA which must be in the keystore (https only). (`true` or `false`).	`false`
`secureSocketProtocol`	Secure protocol that will be used for establishing HTTPS connection (https only)	`TLS`
`keyStoreType`	SSL keystore type to use (https only)	`JKS`
`keyManagerAlgorithm`	Key manager algorithm (https only)	`SunX509`
`trustManagerAlgorithm`	Trust manager algorithm (https only)	`SunX509`
`caCert`	If HTTPs is to be used and no `keystore` is given, then `caCert` can be used to point to a PEM encoded CA certification file. This is use to verify client certificates when `useSslClientAuthentication` is switched on (https only)
`serverCert`	For SSL (and when no `keyStore` is used) then this path must point to server certificate which is presented to clients (https only)
`serverKey`	Path to the PEM encoded key file for signing the server cert during TLS handshake. This is only used when no `keyStore` is used. For decrypting the key the password given with `keystorePassword` is used (https only).
`serverKeyAlgorithm`	Encryption algorithm to use for decrypting the key given with `serverKey` (https only)	`RSA`
`clientPrincipal`	The principal which must be given in a client certificate to allow access to the agent. This can be one or or more relative distinguished names (RDN), separated by commas. The subject of a given client certificate must match on all configured RDNs. For example, when the configuration is `O=jolokia.org,OU=Dev` then a client certificate’s subject must contain `O=jolokia.org` and `OU=Dev` to allow the request. Multiple alternative principals can be configured by using additional options with consecutive index suffix like in `clientPrincipal.1`, `clientPrincipal.2`, … Please remember that a `,` separating RDNs must be escaped with a backslash (`\,`) when used on the commandline as agent arguments. (https and useSslAuthentication only)
`extraClientCheck`	If switched on the agent performs an extra check for client authentication that the presented client cert contains a client flag in the extended key usage section which must be present. (https and useSslAuthentication only)
`bootAmx`	If set to `true` and if the agent is attached to a GlassFish server, then during startup the AMX subsystem is booted so that GlassFish specific MBeans are available. Otherwise, if set to `false` the AMX system is not booted.	`true`
`config`	Path to a properties file from where the configuration options should be read. Such a property file can contain the configuration options as described here as key value pairs (except for the `config` property of course :)
`discoveryEnabled`	If set to `false` then this agent will not listen for multicast request (multicast-group 239.192.48.84, port 24884 by default, but can configured individually). By default this option is enabled. 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.discoveryUrl`. 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://10.9.11.87:8778/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`	`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`	`24884`
`sslProtocol`	The list of SSL / TLS protocols enabled. Valid options are available in the documentation on SunJSSEProvider for your JDK version. Using only `TLSv1.1` and `TLSv1.2` is recommended in Java 1.7 and Java 1.8. Using only `TLSv1` is recommended in Java 1.6. Multiple protocols can be configured by using additional options with consecutive index suffixes like in `sslProtocol.1`, `sslProtocol.2`, …	`TLSv1.2`
`sslCipherSuite`	The list of SSL / TLS cipher suites to enable. The table of available cipher suites is available under the "Default Enabled Cipher Suites" at the SunJSSEProvider documentation here. Multiple cipher suites can be configured by using additional options with consecutive index suffixes like in `sslCipherSuite.1`, `sslCipherSuite.2`, …
`policyLocation`	Path to the XML policy file

Upon successful startup the agent will print out a success message with the full URL which can be used by clients for contacting the agent.

Attaching a Jolokia agent on the fly

Dynamic loading of agents will be removed at some point. See JEP 451 for details.

A Jolokia agent can be attached to any running Java process as long as the user has sufficient access privileges for accessing the process. This agent uses the JVM Attach API for dynamically attaching and detaching to and from the process. It works similar to JConsole or jcmd command connecting to a local process. The Jolokia advantage is, that after the start of the agent, it can be reached over the network.

The JAR containing the JVM agent also contains a client application which can be reached via the -jar option. Call it with --help to get a short usage information:

$ java -jar jolokia-agent-jvm-2.0.2-javaagent.jar --help

Jolokia Agent Launcher
======================

Usage: java -jar jolokia-agent-jvm-2.0.2-javaagent.jar [options] <command> <pid/regexp>

where <command> is one of
    start     -- Start a Jolokia agent for the process specified
    stop      -- Stop a Jolokia agent for the process specified
    status    -- Show status of an (potentially) attached agent
    toggle    -- Toggle between start/stop (default when no command is given)
    list      -- List all attachable Java processes (default when no argument is given at all)
    encrypt   -- Encrypt a password which is given as argument or read from standard input

[options] are used for providing runtime information for attaching the agent:

    --host <host>                   Hostname or IP address to which to bind on
                                    (default: InetAddress.getLocalHost())
    --port <port>                   Port to listen on (default: 8778)
    --agentContext <context>        HTTP Context under which the agent is reachable (default: /jolokia)
    --agentId <agent-id>            VM unique identifier used by this agent (default: autogenerated)
    --agentDescription <desc>       Agent description
    --authMode <mode>               Authentication mode: 'basic' (default), 'jaas' or 'delegate'
    --authMatch <match>             If MultiAuthenticator is used, this config item explains how to combine multiple authenticators
                                     "any" -- at least one authenticator must match (default)
                                     "all" -- all authenticators must match
    --authClass <class>             Classname of an custom Authenticator which must be loadable from the classpath
    --authUrl <url>                 URL used for a dispatcher authentication (authMode == delegate)
    --authPrincipalSpec <spec>      Extractor specification for getting the principal (authMode == delegate)
    --authIgnoreCerts               Whether to ignore CERTS when doing a dispatching authentication (authMode == delegate)
    --user <user>                   User used for Basic-Authentication
    --password <password>           Password used for Basic-Authentication
    --quiet                         No output. "status" will exit with code 0 if the agent is running, 1 otherwise
    --verbose                       Verbose output
    --executor <executor>           Executor policy for HTTP Threads to use (default: single)
                                     "fixed"  -- Thread pool with a fixed number of threads (default: 5)
                                     "cached" -- Cached Thread Pool, creates threads on demand
                                     "single" -- Single Thread
    --threadNamePrefix <prefix>     Thread name prefix that executor will use while creating new thread(s)
                                    (default: jolokia-)
    --threadNr <nr threads>         Number of fixed threads if "fixed" is used as executor
    --backlog <backlog>             How many request to keep in the backlog (default: 10)
    --protocol <http|https>         Protocol which must be either "http" or "https" (default: http)
    --keystore <keystore>           Path to keystore (https only)
    --keystorePassword <pwd>        Password to the keystore (https only)
    --useSslClientAuthentication    Use client certificate authentication (https only)
    --secureSocketProtocol <name>   Secure protocol (https only, default: TLS)
    --keyStoreType <name>           Keystore type (https only, default: JKS)
    --keyManagerAlgorithm <name>    Key manager algorithm (https only, default: SunX509)
    --trustManagerAlgorithm <name>  Trust manager algorithm (https only, default: SunX509)
    --caCert <path>                 Path to a PEM encoded CA cert file (https & sslClientAuth only)
    --serverCert <path>             Path to a PEM encoded server cert file (https only)
    --serverKey <path>              Path to a PEM encoded server key file (https only)
    --serverKeyAlgorithm <algo>     Algorithm to use for decrypting the server key (https only, default: RSA)
    --clientPrincipal <principal>   Allow only this principal in the client cert (https & sslClientAuth only)
                                    If supplied multiple times, any one of the clientPrincipals must match
    --extendedClientCheck <t|f>     Additional validation of client certs for the proper key usage (https & sslClientAuth only)
    --discoveryEnabled <t|f>        Enable/Disable discovery multicast responses (default: false)
    --discoveryAgentUrl <url>       The URL to use for answering discovery requests. Will be autodetected if not given.
    --sslProtocol <protocol>        SSL / TLS protocol to enable, can be provided multiple times
    --sslCipherSuite <suite>        SSL / TLS cipher suite to enable, can be provided multiple times
    --debug                         Switch on agent debugging
    --logHandlerClass <class>       Implementation of org.jolokia.server.core.service.api.LogHandler for logging
                                    Available classes: org.jolokia.server.core.service.impl.QuietLogHandler
                                                       org.jolokia.server.core.service.impl.JulLogHandler
    --logHandlerName <logger name>  A logger name to be used with custom logger implementation
    --debugMaxEntries <nr>          Number of debug entries to keep in memory which can be fetched from the Jolokia MBean
    --maxDepth <depth>              Maximum number of levels for serialization of beans
    --maxCollectionSize <size>      Maximum number of element in collections to keep when serializing the response
    --maxObjects <nr>               Maximum number of objects to consider for serialization
    --restrictorClass <class>       Classname of an custom restrictor which must be loadable from the classpath
    --policyLocation <url>          Location of a Jolokia policy file
    --mbeanQualifier <qualifier>    Qualifier to use when registering Jolokia internal MBeans
    --canonicalNaming <t|f>         whether to use canonicalName for ObjectNames in 'list' or 'search' (default: true)
    --includeStackTrace <t|f>       whether to include StackTraces for error messages (default: false)
    --serializeException <t|f>      whether to add a serialized version of the exception in the Jolokia response (default: false)
    --config <configfile>           Path to a property file from where to read the configuration
    --help                          This help documentation
    --version                       Version of this agent (it's 2.0.2 btw :)

<pid/regexp> can be either a numeric process id or a regular expression. A regular expression is matched
against the processes' names (ignoring case) and must be specific enough to select exactly one process.

If no <command> is given but only a <pid> the state of the Agent will be toggled
between "start" and "stop"

If neither <command> nor <pid> is given, a list of Java processes along with their IDs
is printed

There are several possible reasons, why attaching to a process can fail:
   * The UID of this launcher must be the very *same* as the process to attach to. It's not sufficient to be root.
   * The JVM must have HotSpot enabled and be a JVM 1.6 or later.
   * It must be a Java process ;-)

For more documentation please visit www.jolokia.org

Every option described in Table 1, “JVM agent configuration options” is reflected by a command line option for the launcher. Additionally, the option --quiet can be used to keep the launcher silent and --verbose for adding some extra logging.

The launcher knows various operational modes, which needs to be provided as a non-option argument and possibly require an extra argument.

start: Use this to attach an agent to an already running, local Java process. The additional argument is either the process id of the Java process to attach to or a regular expression which is matched against the Java processes names. In the later case, exactly one process must match, otherwise an exception is raised. The command will return with an return code of 0 if an agent has been started. If the agent is already running, nothing happens and the launcher returns with 1. The URL of the Agent will be printed to standard out on an extra line except when the --quiet option is used.
stop: Command for stopping an running and dynamically attached agent. The required argument is the Java process id or an regular expression as described for the start command. If the agent could be stopped, the launcher exits with 0, it exits with 1 if there was no agent running.
toggle: Starts or stops an dynamically attached agent, depending on its current state. The Java process ID is required as an additional argument. If an agent is running, toggle will stop it (and vice versa). The launcher returns with an exit code of 0 except when the operation fails. When the agent is started, the full agent’s URL is printed to standard out. toggle is the default command when only a numeric process id is given as argument or a regular expression which not the same as a known command.
status: Command for showing the current agent status for a given process. The process id or a regular expression is required. The launcher will return with 0 when the agent is running, otherwise with 1.
list: List all local Java processes in a table with the process id and the description as columns. This is the default command if no non-option argument is given at all. list returns with 0 upon normal operation and with 1 otherwise.
encrypt: Encrypt the keystore password. You can add the password to encrypt as an additional argument or, if not given, it is read from standard input. The output of this command is the encrypted password in the format [[....]], which should be used literally (excluding the final newline) for the keystore password when using the option keystorePassword in the agent configuration.

The launcher is especially suited for one-shot, local queries. For example, a simple shell script for printing out the memory usage of a local Java process, including (temporarily) attaching an Jolokia agent looks simply like in the following example. With a complete client library like jmx4perl even more one shot scripts are possible ^[1].

#!/bin/sh

url=`java -jar jolokia-agent-jvm-2.0.2-javaagent.jar start $1 | tail -1`

memory_url="${url}read/java.lang:type=Memory/HeapMemoryUsage"
used=`curl -s "${memory_url}/used" | jq .value`
max=`curl -s "${memory_url}/max" | jq .value`
usage=$((${used}*100/${max}))
echo "Memory Usage: $usage %"

java -jar jolokia-agent-jvm-2.0.2-javaagent.jar --quiet stop $1

1. And in fact, some support for launching this dynamic agent is planned for a forthcoming release of jmx4perl.