Opentracing across workers (#5771)

Propagate opentracing contexts across workers


Also includes some Convenience modifications to opentracing for servlets, notably:
- Add boolean to skip the whitelisting check on inject
  extract methods. - useful when injecting into carriers
  locally. Otherwise we'd always have to include our
  own servername and whitelist our servername
- start_active_span_from_request instead of header
- Add boolean to decide whether to extract context
  from a request to a servlet

synapse/federation/transport/server.py

@@ -38,7 +38,12 @@ from synapse.http.servlet import (
     parse_string_from_args,
 )
 from synapse.logging.context import run_in_background
-from synapse.logging.opentracing import start_active_span_from_context, tags
+from synapse.logging.opentracing import (
+    start_active_span,
+    start_active_span_from_request,
+    tags,
+    whitelisted_homeserver,
+)
 from synapse.types import ThirdPartyInstanceID, get_domain_from_id
 from synapse.util.ratelimitutils import FederationRateLimiter
 from synapse.util.versionstring import get_version_string
@@ -288,20 +293,28 @@ class BaseFederationServlet(object):
                 logger.warn("authenticate_request failed: %s", e)
                 raise
 
-            # Start an opentracing span
-            with start_active_span_from_context(
-                request.requestHeaders,
-                "incoming-federation-request",
-                tags={
-                    "request_id": request.get_request_id(),
-                    tags.SPAN_KIND: tags.SPAN_KIND_RPC_SERVER,
-                    tags.HTTP_METHOD: request.get_method(),
-                    tags.HTTP_URL: request.get_redacted_uri(),
-                    tags.PEER_HOST_IPV6: request.getClientIP(),
-                    "authenticated_entity": origin,
-                    "servlet_name": request.request_metrics.name,
-                },
-            ):
+            request_tags = {
+                "request_id": request.get_request_id(),
+                tags.SPAN_KIND: tags.SPAN_KIND_RPC_SERVER,
+                tags.HTTP_METHOD: request.get_method(),
+                tags.HTTP_URL: request.get_redacted_uri(),
+                tags.PEER_HOST_IPV6: request.getClientIP(),
+                "authenticated_entity": origin,
+                "servlet_name": request.request_metrics.name,
+            }
+
+            # Only accept the span context if the origin is authenticated
+            # and whitelisted
+            if origin and whitelisted_homeserver(origin):
+                scope = start_active_span_from_request(
+                    request, "incoming-federation-request", tags=request_tags
+                )
+            else:
+                scope = start_active_span(
+                    "incoming-federation-request", tags=request_tags
+                )
+
+            with scope:
                 if origin:
                     with ratelimiter.ratelimit(origin) as d:
                         await d