Add service node name

Whenever a service is composed of multiple instances, there may be a need to distinguish between them for filtering and aggregation purposes.

The context for this issue is https://github.com/elastic/kibana/issues/43765 - a service (eg a web application) may be composed from multiple instances. In APM, we recently introduced dedicated UI for showing JVM specific metrics. Currently, in order to drill down to see specific JVMs, you would need to use the query bar with other fields, that do not always guarantee uniqueness of JVMs (ie service instances). We now want to further enhance the Metrics feature and provide better options for drilling down to individual JVMs. For this purpose, we want to store a unique service instance name.

We are already using the agent fields and in terms of data-correctness we could use agent.id, but it doesn’t really reflect the meaning of that field, which is naming the service instance, and not the agent, so we are not keen on using that. Besides, service instance fields may be valid for agent-less scenarios as well.

Would adding service.instance.name be proper? If so, I assume it would make sense to add service.instance.id as well, but we currently only need the name (we are going to require uniqueness, but it should be a human readable name, therefore - a name rather than an ID).

[roncohen]

OK, let’s start with service.node.name then? Maybe we can have a separate discussion on the elasticsearch node situation. I’d rather not add service.node.id now unless we’re going to make the change to the Elasticsearch module to make use of it imminently.

[simitt]

From the description of service.name:

    The name of the service is normally user given. This allows if two
    instances of the same service are running on the same machine
    they can be differentiated by the `service.name`.

    Also it allows for distributed services that run on multiple hosts to
    correlate the related instances based on the name.

To me this reads contradicting. On the one hand the service.name is supposed to be unique for multiple processes on one machine, on the other hand it should be the same so services over multiple hosts can be matched.

When adding service.node.name I suggest to change the description for service.name to remove this first paragraph from it, as this is exactly what service.node.name is introduced for.