Add basic opentracing support (#5544)

* Configure and initialise tracer

Includes config options for the tracer and sets up JaegerClient.

* Scope manager using LogContexts

We piggy-back our tracer scopes by using log context.
The current log context gives us the current scope. If new scope is
created we create a stack of scopes in the context.

* jaeger is a dependency now

* Carrier inject and extraction for Twisted Headers

* Trace federation requests on the way in and out.

The span is created in _started_processing and closed in
_finished_processing because we need a meaningful log context.

* Create logcontext for new scope.

Instead of having a stack of scopes in a logcontext we create a new
context for a new scope if the current logcontext already has a scope.

* Remove scope from logcontext if logcontext is top level

* Disable tracer if not configured

* typo

* Remove dependence on jaeger internals

* bools

* Set service name

* :Explicitely state that the tracer is disabled

* Black is the new black

* Newsfile

* Code style

* Use the new config setup.

* Generate config.

* Copyright

* Rename config to opentracing

* Remove user whitelisting

* Empty whitelist by default

* User ConfigError instead of RuntimeError

* Use isinstance

* Use tag constants for opentracing.

* Remove debug comment and no need to explicitely record error

* Two errors a "s(c)entry"

* Docstrings!

* Remove debugging brainslip

* Homeserver Whitlisting

* Better opentracing config comment

* linting

* Inclue worker name in service_name

* Make opentracing an optional dependency

* Neater config retreival

* Clean up dummy tags

* Instantiate tracing as object instead of global class

* Inlcude opentracing as a homeserver member.

* Thread opentracing to the request level

* Reference opetnracing through hs

* Instantiate dummy opentracin g for tests.

* About to revert, just keeping the unfinished changes just in case

* Revert back to global state, commit number:

9ce4a3d9067bf9889b86c360c05ac88618b85c4f

* Use class level methods in tracerutils

* Start and stop requests spans in a place where we
have access to the authenticated entity

* Seen it, isort it

* Make sure to close the active span.

* I'm getting black and blue from this.

* Logger formatting

Co-Authored-By: Erik Johnston <erik@matrix.org>

* Outdated comment

* Import opentracing at the top

* Return a contextmanager

* Start tracing client requests from the servlet

* Return noop context manager if not tracing

* Explicitely say that these are federation requests

* Include servlet name in client requests

* Use context manager

* Move opentracing to logging/

* Seen it, isort it again!

* Ignore twisted return exceptions on context exit

* Escape the scope

* Scopes should be entered to make them useful.

* Nicer decorator names

* Just one init, init?

* Don't need to close something that isn't open

* Docs make you smarter

12 files changed, 633 insertions, 12 deletions

diff --git a/changelog.d/5544.misc b/changelog.d/5544.misc
new file mode 100644
index 0000000000..81d6f74c31
--- /dev/null
+++ b/changelog.d/5544.misc
@@ -0,0 +1 @@
+Added opentracing and configuration options.
diff --git a/docs/sample_config.yaml b/docs/sample_config.yaml
index 7fe7c94ac4..0462f0a17a 100644
--- a/docs/sample_config.yaml
+++ b/docs/sample_config.yaml
@@ -1395,3 +1395,20 @@ password_config:
 #  module: "my_custom_project.SuperRulesSet"
 #  config:
 #    example_option: 'things'
+
+
+## Opentracing ##
+# These settings enable opentracing which implements distributed tracing
+# This allows you to observe the causal chain of events across servers
+# including requests, key lookups etc. across any server running
+# synapse or any other other services which supports opentracing.
+# (specifically those implemented with jaeger)
+
+#opentracing:
+#  # Enable / disable tracer
+#  tracer_enabled: false
+#  # The list of homeservers we wish to expose our current traces to.
+#  # The list is a list of regexes which are matched against the
+#  # servername of the homeserver
+#  homeserver_whitelist:
+#    - ".*"
diff --git a/synapse/app/_base.py b/synapse/app/_base.py
index 1ebb7ae539..bd285122ea 100644
--- a/synapse/app/_base.py
+++ b/synapse/app/_base.py
@@ -243,6 +243,9 @@ def start(hs, listeners=None):
         # Load the certificate from disk.
         refresh_certificate(hs)
 
+        # Start the tracer
+        synapse.logging.opentracing.init_tracer(hs.config)
+
         # It is now safe to start your Synapse.
         hs.start_listening(listeners)
         hs.get_datastore().start_profiling()
diff --git a/synapse/config/homeserver.py b/synapse/config/homeserver.py
index acadef4fd3..72acad4f18 100644
--- a/synapse/config/homeserver.py
+++ b/synapse/config/homeserver.py
@@ -40,6 +40,7 @@ from .spam_checker import SpamCheckerConfig
 from .stats import StatsConfig
 from .third_party_event_rules import ThirdPartyRulesConfig
 from .tls import TlsConfig
+from .tracer import TracerConfig
 from .user_directory import UserDirectoryConfig
 from .voip import VoipConfig
 from .workers import WorkerConfig
@@ -75,5 +76,6 @@ class HomeServerConfig(
     ServerNoticesConfig,
     RoomDirectoryConfig,
     ThirdPartyRulesConfig,
+    TracerConfig,
 ):
     pass
diff --git a/synapse/config/tracer.py b/synapse/config/tracer.py
new file mode 100644
index 0000000000..63a637984a
--- /dev/null
+++ b/synapse/config/tracer.py
@@ -0,0 +1,50 @@
+# -*- coding: utf-8 -*-
+# Copyright 2019 The Matrix.org Foundation C.I.C.d
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from ._base import Config, ConfigError
+
+
+class TracerConfig(Config):
+    def read_config(self, config, **kwargs):
+        self.tracer_config = config.get("opentracing")
+
+        self.tracer_config = config.get("opentracing", {"tracer_enabled": False})
+
+        if self.tracer_config.get("tracer_enabled", False):
+            # The tracer is enabled so sanitize the config
+            # If no whitelists are given
+            self.tracer_config.setdefault("homeserver_whitelist", [])
+
+            if not isinstance(self.tracer_config.get("homeserver_whitelist"), list):
+                raise ConfigError("Tracer homesererver_whitelist config is malformed")
+
+    def generate_config_section(cls, **kwargs):
+        return """\
+        ## Opentracing ##
+        # These settings enable opentracing which implements distributed tracing
+        # This allows you to observe the causal chain of events across servers
+        # including requests, key lookups etc. across any server running
+        # synapse or any other other services which supports opentracing.
+        # (specifically those implemented with jaeger)
+
+        #opentracing:
+        #  # Enable / disable tracer
+        #  tracer_enabled: false
+        #  # The list of homeservers we wish to expose our current traces to.
+        #  # The list is a list of regexes which are matched against the
+        #  # servername of the homeserver
+        #  homeserver_whitelist:
+        #    - ".*"
+        """
diff --git a/synapse/federation/transport/server.py b/synapse/federation/transport/server.py
index 2efdcff7ef..c45d458d94 100644
--- a/synapse/federation/transport/server.py
+++ b/synapse/federation/transport/server.py
@@ -21,6 +21,7 @@ import re
 from twisted.internet import defer
 
 import synapse
+import synapse.logging.opentracing as opentracing
 from synapse.api.errors import Codes, FederationDeniedError, SynapseError
 from synapse.api.room_versions import RoomVersions
 from synapse.api.urls import (
@@ -288,14 +289,29 @@ class BaseFederationServlet(object):
                 logger.warn("authenticate_request failed: %s", e)
                 raise
 
-            if origin:
-                with ratelimiter.ratelimit(origin) as d:
-                    yield d
+            # Start an opentracing span
+            with opentracing.start_active_span_from_context(
+                request.requestHeaders,
+                "incoming-federation-request",
+                tags={
+                    "request_id": request.get_request_id(),
+                    opentracing.tags.SPAN_KIND: opentracing.tags.SPAN_KIND_RPC_SERVER,
+                    opentracing.tags.HTTP_METHOD: request.get_method(),
+                    opentracing.tags.HTTP_URL: request.get_redacted_uri(),
+                    opentracing.tags.PEER_HOST_IPV6: request.getClientIP(),
+                    "authenticated_entity": origin,
+                },
+            ):
+                if origin:
+                    with ratelimiter.ratelimit(origin) as d:
+                        yield d
+                        response = yield func(
+                            origin, content, request.args, *args, **kwargs
+                        )
+                else:
                     response = yield func(
                         origin, content, request.args, *args, **kwargs
                     )
-            else:
-                response = yield func(origin, content, request.args, *args, **kwargs)
 
             defer.returnValue(response)
 
diff --git a/synapse/http/matrixfederationclient.py b/synapse/http/matrixfederationclient.py
index dee3710f68..e60334547e 100644
--- a/synapse/http/matrixfederationclient.py
+++ b/synapse/http/matrixfederationclient.py
@@ -36,6 +36,7 @@ from twisted.internet.task import _EPSILON, Cooperator
 from twisted.web._newclient import ResponseDone
 from twisted.web.http_headers import Headers
 
+import synapse.logging.opentracing as opentracing
 import synapse.metrics
 import synapse.util.retryutils
 from synapse.api.errors import (
@@ -339,9 +340,25 @@ class MatrixFederationHttpClient(object):
         else:
             query_bytes = b""
 
-        headers_dict = {b"User-Agent": [self.version_string_bytes]}
+        # Retreive current span
+        scope = opentracing.start_active_span(
+            "outgoing-federation-request",
+            tags={
+                opentracing.tags.SPAN_KIND: opentracing.tags.SPAN_KIND_RPC_CLIENT,
+                opentracing.tags.PEER_ADDRESS: request.destination,
+                opentracing.tags.HTTP_METHOD: request.method,
+                opentracing.tags.HTTP_URL: request.path,
+            },
+            finish_on_close=True,
+        )
+
+        # Inject the span into the headers
+        headers_dict = {}
+        opentracing.inject_active_span_byte_dict(headers_dict, request.destination)
 
-        with limiter:
+        headers_dict[b"User-Agent"] = [self.version_string_bytes]
+
+        with limiter, scope:
             # XXX: Would be much nicer to retry only at the transaction-layer
             # (once we have reliable transactions in place)
             if long_retries:
@@ -419,6 +436,10 @@ class MatrixFederationHttpClient(object):
                         response.phrase.decode("ascii", errors="replace"),
                     )
 
+                    opentracing.set_tag(
+                        opentracing.tags.HTTP_STATUS_CODE, response.code
+                    )
+
                     if 200 <= response.code < 300:
                         pass
                     else:
@@ -499,8 +520,7 @@ class MatrixFederationHttpClient(object):
                         _flatten_response_never_received(e),
                     )
                     raise
-
-            defer.returnValue(response)
+        defer.returnValue(response)
 
     def build_auth_headers(
         self, destination, method, url_bytes, content=None, destination_is=None
diff --git a/synapse/http/servlet.py b/synapse/http/servlet.py
index cd8415acd5..889038ff25 100644
--- a/synapse/http/servlet.py
+++ b/synapse/http/servlet.py
@@ -20,6 +20,7 @@ import logging
 from canonicaljson import json
 
 from synapse.api.errors import Codes, SynapseError
+from synapse.logging.opentracing import trace_servlet
 
 logger = logging.getLogger(__name__)
 
@@ -290,7 +291,11 @@ class RestServlet(object):
             for method in ("GET", "PUT", "POST", "OPTIONS", "DELETE"):
                 if hasattr(self, "on_%s" % (method,)):
                     method_handler = getattr(self, "on_%s" % (method,))
-                    http_server.register_paths(method, patterns, method_handler)
+                    http_server.register_paths(
+                        method,
+                        patterns,
+                        trace_servlet(self.__class__.__name__, method_handler),
+                    )
 
         else:
             raise NotImplementedError("RestServlet must register something.")
diff --git a/synapse/logging/context.py b/synapse/logging/context.py
index 30dfa1d6b2..b456c31f70 100644
--- a/synapse/logging/context.py
+++ b/synapse/logging/context.py
@@ -186,6 +186,7 @@ class LoggingContext(object):
         "alive",
         "request",
         "tag",
+        "scope",
     ]
 
     thread_local = threading.local()
@@ -238,6 +239,7 @@ class LoggingContext(object):
         self.request = None
         self.tag = ""
         self.alive = True
+        self.scope = None
 
         self.parent_context = parent_context
 
@@ -322,10 +324,12 @@ class LoggingContext(object):
         another LoggingContext
         """
 
-        # 'request' is the only field we currently use in the logger, so that's
-        # all we need to copy
+        # we track the current request
         record.request = self.request
 
+        # we also track the current scope:
+        record.scope = self.scope
+
     def start(self):
         if get_thread_id() != self.main_thread:
             logger.warning("Started logcontext %s on different thread", self)
diff --git a/synapse/logging/opentracing.py b/synapse/logging/opentracing.py
new file mode 100644
index 0000000000..f0ceea2a64
--- /dev/null
+++ b/synapse/logging/opentracing.py
@@ -0,0 +1,362 @@
+# -*- coding: utf-8 -*-
+# Copyright 2019 The Matrix.org Foundation C.I.C.d
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.import opentracing
+
+
+# NOTE
+# This is a small wrapper around opentracing because opentracing is not currently
+# packaged downstream (specifically debian). Since opentracing instrumentation is
+# fairly invasive it was awkward to make it optional. As a result we opted to encapsulate
+# all opentracing state in these methods which effectively noop if opentracing is
+# not present. We should strongly consider encouraging the downstream distributers
+# to package opentracing and making opentracing a full dependency. In order to facilitate
+# this move the methods have work very similarly to opentracing's and it should only
+# be a matter of few regexes to move over to opentracing's access patterns proper.
+
+try:
+    import opentracing
+except ImportError:
+    opentracing = None
+try:
+    from jaeger_client import Config as JaegerConfig
+    from synapse.logging.scopecontextmanager import LogContextScopeManager
+except ImportError:
+    JaegerConfig = None
+    LogContextScopeManager = None
+
+import contextlib
+import logging
+import re
+from functools import wraps
+
+from twisted.internet import defer
+
+logger = logging.getLogger(__name__)
+
+
+class _DumTagNames(object):
+    """wrapper of opentracings tags. We need to have them if we
+    want to reference them without opentracing around. Clearly they
+    should never actually show up in a trace. `set_tags` overwrites
+    these with the correct ones."""
+
+    INVALID_TAG = "invalid-tag"
+    COMPONENT = INVALID_TAG
+    DATABASE_INSTANCE = INVALID_TAG
+    DATABASE_STATEMENT = INVALID_TAG
+    DATABASE_TYPE = INVALID_TAG
+    DATABASE_USER = INVALID_TAG
+    ERROR = INVALID_TAG
+    HTTP_METHOD = INVALID_TAG
+    HTTP_STATUS_CODE = INVALID_TAG
+    HTTP_URL = INVALID_TAG
+    MESSAGE_BUS_DESTINATION = INVALID_TAG
+    PEER_ADDRESS = INVALID_TAG
+    PEER_HOSTNAME = INVALID_TAG
+    PEER_HOST_IPV4 = INVALID_TAG
+    PEER_HOST_IPV6 = INVALID_TAG
+    PEER_PORT = INVALID_TAG
+    PEER_SERVICE = INVALID_TAG
+    SAMPLING_PRIORITY = INVALID_TAG
+    SERVICE = INVALID_TAG
+    SPAN_KIND = INVALID_TAG
+    SPAN_KIND_CONSUMER = INVALID_TAG
+    SPAN_KIND_PRODUCER = INVALID_TAG
+    SPAN_KIND_RPC_CLIENT = INVALID_TAG
+    SPAN_KIND_RPC_SERVER = INVALID_TAG
+
+
+def only_if_tracing(func):
+    """Executes the function only if we're tracing. Otherwise return.
+    Assumes the function wrapped may return None"""
+
+    @wraps(func)
+    def _only_if_tracing_inner(*args, **kwargs):
+        if opentracing:
+            return func(*args, **kwargs)
+        else:
+            return
+
+    return _only_if_tracing_inner
+
+
+# Block everything by default
+_homeserver_whitelist = None
+
+tags = _DumTagNames
+
+
+def init_tracer(config):
+    """Set the whitelists and initialise the JaegerClient tracer
+
+    Args:
+        config (Config)
+        The config used by the homeserver. Here it's used to set the service
+        name to the homeserver's.
+    """
+    global opentracing
+    if not config.tracer_config.get("tracer_enabled", False):
+        # We don't have a tracer
+        opentracing = None
+        return
+
+    if not opentracing:
+        logger.error(
+            "The server has been configure to use opentracing but opentracing is not installed."
+        )
+        raise ModuleNotFoundError("opentracing")
+
+    if not JaegerConfig:
+        logger.error(
+            "The server has been configure to use opentracing but opentracing is not installed."
+        )
+
+    # Include the worker name
+    name = config.worker_name if config.worker_name else "master"
+
+    set_homeserver_whitelist(config.tracer_config["homeserver_whitelist"])
+    jaeger_config = JaegerConfig(
+        config={"sampler": {"type": "const", "param": 1}, "logging": True},
+        service_name="{} {}".format(config.server_name, name),
+        scope_manager=LogContextScopeManager(config),
+    )
+    jaeger_config.initialize_tracer()
+
+    # Set up tags to be opentracing's tags
+    global tags
+    tags = opentracing.tags
+
+
+@contextlib.contextmanager
+def _noop_context_manager(*args, **kwargs):
+    """Does absolutely nothing really well. Can be entered and exited arbitrarily.
+    Good substitute for an opentracing scope."""
+    yield
+
+
+# Could use kwargs but I want these to be explicit
+def start_active_span(
+    operation_name,
+    child_of=None,
+    references=None,
+    tags=None,
+    start_time=None,
+    ignore_active_span=False,
+    finish_on_close=True,
+):
+    """Starts an active opentracing span. Note, the scope doesn't become active
+    until it has been entered, however, the span starts from the time this
+    message is called.
+    Args:
+        See opentracing.tracer
+    Returns:
+        scope (Scope) or noop_context_manager
+    """
+    if opentracing is None:
+        return _noop_context_manager()
+    else:
+        # We need to enter the scope here for the logcontext to become active
+        return opentracing.tracer.start_active_span(
+            operation_name,
+            child_of=child_of,
+            references=references,
+            tags=tags,
+            start_time=start_time,
+            ignore_active_span=ignore_active_span,
+            finish_on_close=finish_on_close,
+        )
+
+
+@only_if_tracing
+def close_active_span():
+    """Closes the active span. This will close it's logcontext if the context
+    was made for the span"""
+    opentracing.tracer.scope_manager.active.__exit__(None, None, None)
+
+
+@only_if_tracing
+def set_tag(key, value):
+    """Set's a tag on the active span"""
+    opentracing.tracer.active_span.set_tag(key, value)
+
+
+@only_if_tracing
+def log_kv(key_values, timestamp=None):
+    """Log to the active span"""
+    opentracing.tracer.active_span.log_kv(key_values, timestamp)
+
+
+# Note: we don't have a get baggage items because we're trying to hide all
+# scope and span state from synapse. I think this method may also be useless
+# as a result
+@only_if_tracing
+def set_baggage_item(key, value):
+    """Attach baggage to the active span"""
+    opentracing.tracer.active_span.set_baggage_item(key, value)
+
+
+@only_if_tracing
+def set_operation_name(operation_name):
+    """Sets the operation name of the active span"""
+    opentracing.tracer.active_span.set_operation_name(operation_name)
+
+
+@only_if_tracing
+def set_homeserver_whitelist(homeserver_whitelist):
+    """Sets the whitelist
+
+    Args:
+        homeserver_whitelist (iterable of strings): regex of whitelisted homeservers
+    """
+    global _homeserver_whitelist
+    if homeserver_whitelist:
+        # Makes a single regex which accepts all passed in regexes in the list
+        _homeserver_whitelist = re.compile(
+            "({})".format(")|(".join(homeserver_whitelist))
+        )
+
+
+@only_if_tracing
+def whitelisted_homeserver(destination):
+    """Checks if a destination matches the whitelist
+    Args:
+        destination (String)"""
+    global _homeserver_whitelist
+    if _homeserver_whitelist:
+        return _homeserver_whitelist.match(destination)
+    return False
+
+
+def start_active_span_from_context(
+    headers,
+    operation_name,
+    references=None,
+    tags=None,
+    start_time=None,
+    ignore_active_span=False,
+    finish_on_close=True,
+):
+    """
+    Extracts a span context from Twisted Headers.
+    args:
+        headers (twisted.web.http_headers.Headers)
+    returns:
+        span_context (opentracing.span.SpanContext)
+    """
+    # Twisted encodes the values as lists whereas opentracing doesn't.
+    # So, we take the first item in the list.
+    # Also, twisted uses byte arrays while opentracing expects strings.
+    if opentracing is None:
+        return _noop_context_manager()
+
+    header_dict = {k.decode(): v[0].decode() for k, v in headers.getAllRawHeaders()}
+    context = opentracing.tracer.extract(opentracing.Format.HTTP_HEADERS, header_dict)
+
+    return opentracing.tracer.start_active_span(
+        operation_name,
+        child_of=context,
+        references=references,
+        tags=tags,
+        start_time=start_time,
+        ignore_active_span=ignore_active_span,
+        finish_on_close=finish_on_close,
+    )
+
+
+@only_if_tracing
+def inject_active_span_twisted_headers(headers, destination):
+    """
+    Injects a span context into twisted headers inplace
+
+    Args:
+        headers (twisted.web.http_headers.Headers)
+        span (opentracing.Span)
+
+    Returns:
+        Inplace modification of headers
+
+    Note:
+        The headers set by the tracer are custom to the tracer implementation which
+        should be unique enough that they don't interfere with any headers set by
+        synapse or twisted. If we're still using jaeger these headers would be those
+        here:
+        https://github.com/jaegertracing/jaeger-client-python/blob/master/jaeger_client/constants.py
+    """
+
+    if not whitelisted_homeserver(destination):
+        return
+
+    span = opentracing.tracer.active_span
+    carrier = {}
+    opentracing.tracer.inject(span, opentracing.Format.HTTP_HEADERS, carrier)
+
+    for key, value in carrier.items():
+        headers.addRawHeaders(key, value)
+
+
+@only_if_tracing
+def inject_active_span_byte_dict(headers, destination):
+    """
+    Injects a span context into a dict where the headers are encoded as byte
+    strings
+
+    Args:
+        headers (dict)
+        span (opentracing.Span)
+
+    Returns:
+        Inplace modification of headers
+
+    Note:
+        The headers set by the tracer are custom to the tracer implementation which
+        should be unique enough that they don't interfere with any headers set by
+        synapse or twisted. If we're still using jaeger these headers would be those
+        here:
+        https://github.com/jaegertracing/jaeger-client-python/blob/master/jaeger_client/constants.py
+    """
+    if not whitelisted_homeserver(destination):
+        return
+
+    span = opentracing.tracer.active_span
+
+    carrier = {}
+    opentracing.tracer.inject(span, opentracing.Format.HTTP_HEADERS, carrier)
+
+    for key, value in carrier.items():
+        headers[key.encode()] = [value.encode()]
+
+
+def trace_servlet(servlet_name, func):
+    """Decorator which traces a serlet. It starts a span with some servlet specific
+    tags such as the servlet_name and request information"""
+
+    @wraps(func)
+    @defer.inlineCallbacks
+    def _trace_servlet_inner(request, *args, **kwargs):
+        with start_active_span_from_context(
+            request.requestHeaders,
+            "incoming-client-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(),
+                "servlet_name": servlet_name,
+            },
+        ):
+            result = yield defer.maybeDeferred(func, request, *args, **kwargs)
+        defer.returnValue(result)
+
+    return _trace_servlet_inner
diff --git a/synapse/logging/scopecontextmanager.py b/synapse/logging/scopecontextmanager.py
new file mode 100644
index 0000000000..91e14462f3
--- /dev/null
+++ b/synapse/logging/scopecontextmanager.py
@@ -0,0 +1,140 @@
+# -*- coding: utf-8 -*-
+# Copyright 2019 The Matrix.org Foundation C.I.C.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.import logging
+
+import logging
+
+from opentracing import Scope, ScopeManager
+
+import twisted
+
+from synapse.logging.context import LoggingContext, nested_logging_context
+
+logger = logging.getLogger(__name__)
+
+
+class LogContextScopeManager(ScopeManager):
+    """
+    The LogContextScopeManager tracks the active scope in opentracing
+    by using the log contexts which are native to synapse. This is so
+    that the basic opentracing api can be used across twisted defereds.
+    (I would love to break logcontexts and this into an OS package. but
+    let's wait for twisted's contexts to be released.)
+    """
+
+    def __init__(self, config):
+        # Set the whitelists
+        logger.info(config.tracer_config)
+        self._homeserver_whitelist = config.tracer_config["homeserver_whitelist"]
+
+    @property
+    def active(self):
+        """
+        Returns the currently active Scope which can be used to access the
+        currently active Scope.span.
+        If there is a non-null Scope, its wrapped Span
+        becomes an implicit parent of any newly-created Span at
+        Tracer.start_active_span() time.
+
+        Return:
+            (Scope) : the Scope that is active, or None if not
+            available.
+        """
+        ctx = LoggingContext.current_context()
+        if ctx is LoggingContext.sentinel:
+            return None
+        else:
+            return ctx.scope
+
+    def activate(self, span, finish_on_close):
+        """
+        Makes a Span active.
+        Args
+            span (Span): the span that should become active.
+            finish_on_close (Boolean): whether Span should be automatically
+                finished when Scope.close() is called.
+
+        Returns:
+            Scope to control the end of the active period for
+            *span*. It is a programming error to neglect to call
+            Scope.close() on the returned instance.
+        """
+
+        enter_logcontext = False
+        ctx = LoggingContext.current_context()
+
+        if ctx is LoggingContext.sentinel:
+            # We don't want this scope to affect.
+            logger.error("Tried to activate scope outside of loggingcontext")
+            return Scope(None, span)
+        elif ctx.scope is not None:
+            # We want the logging scope to look exactly the same so we give it
+            # a blank suffix
+            ctx = nested_logging_context("")
+            enter_logcontext = True
+
+        scope = _LogContextScope(self, span, ctx, enter_logcontext, finish_on_close)
+        ctx.scope = scope
+        return scope
+
+
+class _LogContextScope(Scope):
+    """
+    A custom opentracing scope. The only significant difference is that it will
+    close the log context it's related to if the logcontext was created specifically
+    for this scope.
+    """
+
+    def __init__(self, manager, span, logcontext, enter_logcontext, finish_on_close):
+        """
+        Args:
+            manager (LogContextScopeManager):
+                the manager that is responsible for this scope.
+            span (Span):
+                the opentracing span which this scope represents the local
+                lifetime for.
+            logcontext (LogContext):
+                the logcontext to which this scope is attached.
+            enter_logcontext (Boolean):
+                if True the logcontext will be entered and exited when the scope
+                is entered and exited respectively
+            finish_on_close (Boolean):
+                if True finish the span when the scope is closed
+        """
+        super(_LogContextScope, self).__init__(manager, span)
+        self.logcontext = logcontext
+        self._finish_on_close = finish_on_close
+        self._enter_logcontext = enter_logcontext
+
+    def __enter__(self):
+        if self._enter_logcontext:
+            self.logcontext.__enter__()
+
+    def __exit__(self, type, value, traceback):
+        if type == twisted.internet.defer._DefGen_Return:
+            super(_LogContextScope, self).__exit__(None, None, None)
+        else:
+            super(_LogContextScope, self).__exit__(type, value, traceback)
+        if self._enter_logcontext:
+            self.logcontext.__exit__(type, value, traceback)
+        else:  # the logcontext existed before the creation of the scope
+            self.logcontext.scope = None
+
+    def close(self):
+        if self.manager.active is not self:
+            logger.error("Tried to close a none active scope!")
+            return
+
+        if self._finish_on_close:
+            self.span.finish()
diff --git a/synapse/python_dependencies.py b/synapse/python_dependencies.py
index 6324c00ef1..e7618057be 100644
--- a/synapse/python_dependencies.py
+++ b/synapse/python_dependencies.py
@@ -95,6 +95,7 @@ CONDITIONAL_REQUIREMENTS = {
     "url_preview": ["lxml>=3.5.0"],
     "test": ["mock>=2.0", "parameterized"],
     "sentry": ["sentry-sdk>=0.7.2"],
+    "opentracing": ["jaeger-client>=4.0.0", "opentracing>=2.2.0"],
     "jwt": ["pyjwt>=1.6.4"],
 }