collision in App#brokenInstanceMap causes jmx config to be ignored.

[jcrobak]

We have two jmx config files that match (via autodiscovery) a single JVM. During startup, we sometime see errors in the datadog agent log like (note that there are two different checks, check1 and check2):

2019-10-22 15:05:31 UTC | CORE | INFO | (pkg/jmxfetch/jmxfetch.go:216 in func1) | 2019-10-22 15:05:31,684 | INFO | App | Could not initialize instance: check1-x.x.x.x-yyyy: java.util.concurrent.ExecutionException: java.io.IOException: java.io.IOException: Failed to retrieve RMIServer stub: javax.naming.ServiceUnavailableException [Root exception is java.rmi.ConnectException: Connection refused to host: x.x.x.x; nested exception is:
2019-10-22 15:05:31 UTC | CORE | INFO | (pkg/jmxfetch/jmxfetch.go:216 in func1) | 2019-10-22 15:05:31,684 | INFO | App | Could not initialize instance: check2-x.x.x.x-yyyy: java.util.concurrent.ExecutionException: java.io.IOException: java.io.IOException: Failed to retrieve RMIServer stub: javax.naming.ServiceUnavailableException [Root exception is java.rmi.ConnectException: Connection refused to host: x.x.x.x; nested exception is: 

Looking at App.java, two lines after that message, the instance is put in brokenInstanceMap:

https://github.com/DataDog/jmxfetch/blob/f59dacea44d70f6b19a76a4360d752ef4c27b965/src/main/java/org/datadog/jmxfetch/App.java#L1032-L1036

In our case, instance.toString() resolves to ${host}:${port}, which is not unique across the two checks:

https://github.com/DataDog/jmxfetch/blob/f59dacea44d70f6b19a76a4360d752ef4c27b965/src/main/java/org/datadog/jmxfetch/Instance.java#L395

We tried to set Instance.getName() to something unique (see below), but that didn't solve the problem because Instance.toString() doesn't take into account the name...

instances:
  - host: '%%host%%'
    port: '9999'
    name: 'check1-%%host%%-9999'

A workaround is to combine the two JMX check configs into a single file.

[remeh]

Hey @jcrobak , thanks for having opened an issue! We're looking into this and I'll keep you informed.

[remeh]

With #255, I've merged the change to the Instance.toString() method in order to use the configured instance name if one has been provided. I've also released JMXFetch 0.33.1 to ship this change.

It will be available starting with the Datadog Agent 6.16.0 (PR: https://github.com/DataDog/datadog-agent/pull/4530) which should be released soon.

If you want to test it sooner, you can:

• download the latest 0.33.1 on bintray
• use the jmx_custom_jars configuration field in the Datadog Agent to provide the path to e.g.

  
  jmx_custom_jars:

• /path/to/the/custom/jmxfetch-0.33.1-jar-with-dependencies.jar

  
  Nnote that you can also use the environment variable `DD_JMX_CUSTOM_JARS` or that it could also be configured in a check: https://docs.datadoghq.com/integrations/java/?tab=host#configuration-options

Please let me know when you'll have the chance to test this!