Implement a structured logging output system. (#5680)

1 files changed, 278 insertions, 0 deletions

diff --git a/synapse/logging/_terse_json.py b/synapse/logging/_terse_json.py
new file mode 100644
index 0000000000..7f1e8f23fe
--- /dev/null
+++ b/synapse/logging/_terse_json.py
@@ -0,0 +1,278 @@
+# -*- 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.
+
+"""
+Log formatters that output terse JSON.
+"""
+
+import sys
+from collections import deque
+from ipaddress import IPv4Address, IPv6Address, ip_address
+from math import floor
+from typing.io import TextIO
+
+import attr
+from simplejson import dumps
+
+from twisted.application.internet import ClientService
+from twisted.internet.endpoints import (
+    HostnameEndpoint,
+    TCP4ClientEndpoint,
+    TCP6ClientEndpoint,
+)
+from twisted.internet.protocol import Factory, Protocol
+from twisted.logger import FileLogObserver, Logger
+from twisted.python.failure import Failure
+
+
+def flatten_event(event: dict, metadata: dict, include_time: bool = False):
+    """
+    Flatten a Twisted logging event to an dictionary capable of being sent
+    as a log event to a logging aggregation system.
+
+    The format is vastly simplified and is not designed to be a "human readable
+    string" in the sense that traditional logs are. Instead, the structure is
+    optimised for searchability and filtering, with human-understandable log
+    keys.
+
+    Args:
+        event (dict): The Twisted logging event we are flattening.
+        metadata (dict): Additional data to include with each log message. This
+            can be information like the server name. Since the target log
+            consumer does not know who we are other than by host IP, this
+            allows us to forward through static information.
+        include_time (bool): Should we include the `time` key? If False, the
+            event time is stripped from the event.
+    """
+    new_event = {}
+
+    # If it's a failure, make the new event's log_failure be the traceback text.
+    if "log_failure" in event:
+        new_event["log_failure"] = event["log_failure"].getTraceback()
+
+    # If it's a warning, copy over a string representation of the warning.
+    if "warning" in event:
+        new_event["warning"] = str(event["warning"])
+
+    # Stdlib logging events have "log_text" as their human-readable portion,
+    # Twisted ones have "log_format". For now, include the log_format, so that
+    # context only given in the log format (e.g. what is being logged) is
+    # available.
+    if "log_text" in event:
+        new_event["log"] = event["log_text"]
+    else:
+        new_event["log"] = event["log_format"]
+
+    # We want to include the timestamp when forwarding over the network, but
+    # exclude it when we are writing to stdout. This is because the log ingester
+    # (e.g. logstash, fluentd) can add its own timestamp.
+    if include_time:
+        new_event["time"] = round(event["log_time"], 2)
+
+    # Convert the log level to a textual representation.
+    new_event["level"] = event["log_level"].name.upper()
+
+    # Ignore these keys, and do not transfer them over to the new log object.
+    # They are either useless (isError), transferred manually above (log_time,
+    # log_level, etc), or contain Python objects which are not useful for output
+    # (log_logger, log_source).
+    keys_to_delete = [
+        "isError",
+        "log_failure",
+        "log_format",
+        "log_level",
+        "log_logger",
+        "log_source",
+        "log_system",
+        "log_time",
+        "log_text",
+        "observer",
+        "warning",
+    ]
+
+    # If it's from the Twisted legacy logger (twisted.python.log), it adds some
+    # more keys we want to purge.
+    if event.get("log_namespace") == "log_legacy":
+        keys_to_delete.extend(["message", "system", "time"])
+
+    # Rather than modify the dictionary in place, construct a new one with only
+    # the content we want. The original event should be considered 'frozen'.
+    for key in event.keys():
+
+        if key in keys_to_delete:
+            continue
+
+        if isinstance(event[key], (str, int, bool, float)) or event[key] is None:
+            # If it's a plain type, include it as is.
+            new_event[key] = event[key]
+        else:
+            # If it's not one of those basic types, write out a string
+            # representation. This should probably be a warning in development,
+            # so that we are sure we are only outputting useful data.
+            new_event[key] = str(event[key])
+
+    # Add the metadata information to the event (e.g. the server_name).
+    new_event.update(metadata)
+
+    return new_event
+
+
+def TerseJSONToConsoleLogObserver(outFile: TextIO, metadata: dict) -> FileLogObserver:
+    """
+    A log observer that formats events to a flattened JSON representation.
+
+    Args:
+        outFile: The file object to write to.
+        metadata: Metadata to be added to each log object.
+    """
+
+    def formatEvent(_event: dict) -> str:
+        flattened = flatten_event(_event, metadata)
+        return dumps(flattened, ensure_ascii=False, separators=(",", ":")) + "\n"
+
+    return FileLogObserver(outFile, formatEvent)
+
+
+@attr.s
+class TerseJSONToTCPLogObserver(object):
+    """
+    An IObserver that writes JSON logs to a TCP target.
+
+    Args:
+        hs (HomeServer): The Homeserver that is being logged for.
+        host: The host of the logging target.
+        port: The logging target's port.
+        metadata: Metadata to be added to each log entry.
+    """
+
+    hs = attr.ib()
+    host = attr.ib(type=str)
+    port = attr.ib(type=int)
+    metadata = attr.ib(type=dict)
+    maximum_buffer = attr.ib(type=int)
+    _buffer = attr.ib(default=attr.Factory(deque), type=deque)
+    _writer = attr.ib(default=None)
+    _logger = attr.ib(default=attr.Factory(Logger))
+
+    def start(self) -> None:
+
+        # Connect without DNS lookups if it's a direct IP.
+        try:
+            ip = ip_address(self.host)
+            if isinstance(ip, IPv4Address):
+                endpoint = TCP4ClientEndpoint(
+                    self.hs.get_reactor(), self.host, self.port
+                )
+            elif isinstance(ip, IPv6Address):
+                endpoint = TCP6ClientEndpoint(
+                    self.hs.get_reactor(), self.host, self.port
+                )
+        except ValueError:
+            endpoint = HostnameEndpoint(self.hs.get_reactor(), self.host, self.port)
+
+        factory = Factory.forProtocol(Protocol)
+        self._service = ClientService(endpoint, factory, clock=self.hs.get_reactor())
+        self._service.startService()
+
+    def _write_loop(self) -> None:
+        """
+        Implement the write loop.
+        """
+        if self._writer:
+            return
+
+        self._writer = self._service.whenConnected()
+
+        @self._writer.addBoth
+        def writer(r):
+            if isinstance(r, Failure):
+                r.printTraceback(file=sys.__stderr__)
+                self._writer = None
+                self.hs.get_reactor().callLater(1, self._write_loop)
+                return
+
+            try:
+                for event in self._buffer:
+                    r.transport.write(
+                        dumps(event, ensure_ascii=False, separators=(",", ":")).encode(
+                            "utf8"
+                        )
+                    )
+                    r.transport.write(b"\n")
+                self._buffer.clear()
+            except Exception as e:
+                sys.__stderr__.write("Failed writing out logs with %s\n" % (str(e),))
+
+            self._writer = False
+            self.hs.get_reactor().callLater(1, self._write_loop)
+
+    def _handle_pressure(self) -> None:
+        """
+        Handle backpressure by shedding events.
+
+        The buffer will, in this order, until the buffer is below the maximum:
+            - Shed DEBUG events
+            - Shed INFO events
+            - Shed the middle 50% of the events.
+        """
+        if len(self._buffer) <= self.maximum_buffer:
+            return
+
+        # Strip out DEBUGs
+        self._buffer = deque(
+            filter(lambda event: event["level"] != "DEBUG", self._buffer)
+        )
+
+        if len(self._buffer) <= self.maximum_buffer:
+            return
+
+        # Strip out INFOs
+        self._buffer = deque(
+            filter(lambda event: event["level"] != "INFO", self._buffer)
+        )
+
+        if len(self._buffer) <= self.maximum_buffer:
+            return
+
+        # Cut the middle entries out
+        buffer_split = floor(self.maximum_buffer / 2)
+
+        old_buffer = self._buffer
+        self._buffer = deque()
+
+        for i in range(buffer_split):
+            self._buffer.append(old_buffer.popleft())
+
+        end_buffer = []
+        for i in range(buffer_split):
+            end_buffer.append(old_buffer.pop())
+
+        self._buffer.extend(reversed(end_buffer))
+
+    def __call__(self, event: dict) -> None:
+        flattened = flatten_event(event, self.metadata, include_time=True)
+        self._buffer.append(flattened)
+
+        # Handle backpressure, if it exists.
+        try:
+            self._handle_pressure()
+        except Exception:
+            # If handling backpressure fails,clear the buffer and log the
+            # exception.
+            self._buffer.clear()
+            self._logger.failure("Failed clearing backpressure")
+
+        # Try and write immediately.
+        self._write_loop()