Make virtual_node label value configurable?

[ShyunnY]

When using service_graph, we usually find that the entry nodes are all virtual_node type (of course, this is expected), and their values ​​are always user/peer values.

Is it possible for us to add a new feature that allows users to step in and configure its value?

Describe the solution you'd like

We always use the user-configured value first, if the user selects empty, we can fall back to the default value.

Can we organize it with the following structure? (Of course, this is just an example, not the final form):

service_graphs:
  virtual_node:
    defaultClientValue: foo
    defaultServerValue: bar

Describe alternatives you've considered

None

Additional context

Related code:

tempo/modules/generator/processor/servicegraphs/servicegraphs.go

Lines 390 to 421 in c34cf3a

	func (p *Processor) onExpire(e *store.Edge) {
	p.metricExpiredEdges.Inc()
	// If an edge is expired, we check if there are signs that the missing span is belongs to a "virtual node".
	// These are nodes that are outside the user's reach (eg. an external service for payment processing),
	// or that are not instrumented (eg. a frontend application).
	e.ConnectionType = store.VirtualNode
	if len(e.ClientService) == 0 {
	// If the client service is not set, it means that the span could have been initiated by an external system,
	// like a frontend application or an engineer via `curl`.
	// We check if the span we have is the root span, and if so, we set the client service to "user".
	if _, parentSpan := parseKey(e.Key()); len(parentSpan) == 0 {
	e.ClientService = "user"
	if p.Cfg.EnableVirtualNodeLabel {
	e.Dimensions[virtualNodeLabel] = "client"
	}
	p.onComplete(e)
	}
	} else if len(e.ServerService) == 0 && len(e.PeerNode) > 0 {
	// If client span does not have its matching server span, but has a peer attribute present,
	// we make the assumption that a call was made to an external service, for which Tempo won't receive spans.
	e.ServerService = e.PeerNode
	if p.Cfg.EnableVirtualNodeLabel {
	e.Dimensions[virtualNodeLabel] = "server"
	}
	p.onComplete(e)
	}
	}

[joe-elliott]

Are you saying you'd like a config option to change the hardcoded defaults? I'm good on that.