Strip number suffix from instance name to consolidate services that traces are spread over (#13729)

The problem with many services is that it makes it hard to find which service has the trace you want, see jaegertracing/jaeger-ui#985

Previously, we split traces out into services based on their instance name like `matrix.org client_reader-1`, etc but there are many worker instances of the same `client_reader` so there is a lot to click through.

With this PR, all of the traces are just collected under the worker type like `client_reader`, `event_persister` 😇

Note: A Synapse worker instance name is an opaque string with the number convention only being our own thing for the `matrix.org` deployment. But seems pretty sensible to group things this way.

Author: MadLittleMods

changelog.d/13729.misc

@@ -0,0 +1 @@
+Strip number suffix from instance name to consolidate services that traces are spread over.

synapse/logging/opentracing.py

@@ -203,6 +203,9 @@ def set_fates(clotho, lachesis, atropos, father="Zues", mother="Themis"):
 
 # Helper class
 
+# Matches the number suffix in an instance name like "matrix.org client_reader-8"
+STRIP_INSTANCE_NUMBER_SUFFIX_REGEX = re.compile(r"[_-]?\d+$")
+
 
 class _DummyTagNames:
     """wrapper of opentracings tags. We need to have them if we
@@ -441,9 +444,17 @@ def init_tracer(hs: "HomeServer") -> None:
 
     from jaeger_client.metrics.prometheus import PrometheusMetricsFactory
 
+    # Instance names are opaque strings but by stripping off the number suffix,
+    # we can get something that looks like a "worker type", e.g.
+    # "client_reader-1" -> "client_reader" so we don't spread the traces across
+    # so many services.
+    instance_name_by_type = re.sub(
+        STRIP_INSTANCE_NUMBER_SUFFIX_REGEX, "", hs.get_instance_name()
+    )
+
     config = JaegerConfig(
         config=hs.config.tracing.jaeger_config,
-        service_name=f"{hs.config.server.server_name} {hs.get_instance_name()}",
+        service_name=f"{hs.config.server.server_name} {instance_name_by_type}",
         scope_manager=LogContextScopeManager(),
         metrics_factory=PrometheusMetricsFactory(),
     )