386 lines
13 KiB
Python
386 lines
13 KiB
Python
# Copyright 2015, 2016 OpenMarket Ltd
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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import collections
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import contextlib
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import logging
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import threading
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import typing
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from typing import (
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Any,
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Callable,
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DefaultDict,
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Dict,
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Iterator,
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List,
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Mapping,
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Optional,
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Set,
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Tuple,
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)
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from prometheus_client.core import Counter
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from typing_extensions import ContextManager
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from twisted.internet import defer
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from synapse.api.errors import LimitExceededError
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from synapse.config.ratelimiting import FederationRatelimitSettings
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from synapse.logging.context import (
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PreserveLoggingContext,
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make_deferred_yieldable,
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run_in_background,
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)
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from synapse.logging.opentracing import start_active_span
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from synapse.metrics import Histogram, LaterGauge
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from synapse.util import Clock
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if typing.TYPE_CHECKING:
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from contextlib import _GeneratorContextManager
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logger = logging.getLogger(__name__)
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# Track how much the ratelimiter is affecting requests
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rate_limit_sleep_counter = Counter(
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"synapse_rate_limit_sleep",
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"Number of requests slept by the rate limiter",
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["rate_limiter_name"],
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)
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rate_limit_reject_counter = Counter(
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"synapse_rate_limit_reject",
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"Number of requests rejected by the rate limiter",
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["rate_limiter_name"],
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)
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queue_wait_timer = Histogram(
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"synapse_rate_limit_queue_wait_time_seconds",
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"Amount of time spent waiting for the rate limiter to let our request through.",
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["rate_limiter_name"],
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buckets=(
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0.005,
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0.01,
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0.025,
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0.05,
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0.1,
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0.25,
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0.5,
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0.75,
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1.0,
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2.5,
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5.0,
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10.0,
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20.0,
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"+Inf",
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),
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)
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_rate_limiter_instances: Set["FederationRateLimiter"] = set()
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# Protects the _rate_limiter_instances set from concurrent access
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_rate_limiter_instances_lock = threading.Lock()
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def _get_counts_from_rate_limiter_instance(
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count_func: Callable[["FederationRateLimiter"], int]
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) -> Mapping[Tuple[str, ...], int]:
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"""Returns a count of something (slept/rejected hosts) by (metrics_name)"""
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# Cast to a list to prevent it changing while the Prometheus
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# thread is collecting metrics
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with _rate_limiter_instances_lock:
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rate_limiter_instances = list(_rate_limiter_instances)
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# Map from (metrics_name,) -> int, the number of something like slept hosts
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# or rejected hosts. The key type is Tuple[str], but we leave the length
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# unspecified for compatability with LaterGauge's annotations.
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counts: Dict[Tuple[str, ...], int] = {}
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for rate_limiter_instance in rate_limiter_instances:
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# Only track metrics if they provided a `metrics_name` to
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# differentiate this instance of the rate limiter.
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if rate_limiter_instance.metrics_name:
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key = (rate_limiter_instance.metrics_name,)
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counts[key] = count_func(rate_limiter_instance)
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return counts
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# We track the number of affected hosts per time-period so we can
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# differentiate one really noisy homeserver from a general
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# ratelimit tuning problem across the federation.
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LaterGauge(
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"synapse_rate_limit_sleep_affected_hosts",
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"Number of hosts that had requests put to sleep",
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["rate_limiter_name"],
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lambda: _get_counts_from_rate_limiter_instance(
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lambda rate_limiter_instance: sum(
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ratelimiter.should_sleep()
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for ratelimiter in rate_limiter_instance.ratelimiters.values()
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)
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),
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)
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LaterGauge(
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"synapse_rate_limit_reject_affected_hosts",
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"Number of hosts that had requests rejected",
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["rate_limiter_name"],
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lambda: _get_counts_from_rate_limiter_instance(
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lambda rate_limiter_instance: sum(
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ratelimiter.should_reject()
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for ratelimiter in rate_limiter_instance.ratelimiters.values()
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)
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),
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)
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class FederationRateLimiter:
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"""Used to rate limit request per-host."""
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def __init__(
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self,
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clock: Clock,
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config: FederationRatelimitSettings,
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metrics_name: Optional[str] = None,
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):
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"""
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Args:
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clock
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config
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metrics_name: The name of the rate limiter so we can differentiate it
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from the rest in the metrics. If `None`, we don't track metrics
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for this rate limiter.
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"""
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self.metrics_name = metrics_name
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def new_limiter() -> "_PerHostRatelimiter":
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return _PerHostRatelimiter(
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clock=clock, config=config, metrics_name=metrics_name
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)
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self.ratelimiters: DefaultDict[
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str, "_PerHostRatelimiter"
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] = collections.defaultdict(new_limiter)
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with _rate_limiter_instances_lock:
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_rate_limiter_instances.add(self)
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def ratelimit(self, host: str) -> "_GeneratorContextManager[defer.Deferred[None]]":
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"""Used to ratelimit an incoming request from a given host
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Example usage:
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with rate_limiter.ratelimit(origin) as wait_deferred:
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yield wait_deferred
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# Handle request ...
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Args:
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host: Origin of incoming request.
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Returns:
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context manager which returns a deferred.
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"""
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return self.ratelimiters[host].ratelimit(host)
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class _PerHostRatelimiter:
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def __init__(
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self,
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clock: Clock,
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config: FederationRatelimitSettings,
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metrics_name: Optional[str] = None,
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):
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"""
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Args:
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clock
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config
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metrics_name: The name of the rate limiter so we can differentiate it
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from the rest in the metrics. If `None`, we don't track metrics
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for this rate limiter.
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from the rest in the metrics
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"""
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self.clock = clock
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self.metrics_name = metrics_name
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self.window_size = config.window_size
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self.sleep_limit = config.sleep_limit
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self.sleep_sec = config.sleep_delay / 1000.0
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self.reject_limit = config.reject_limit
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self.concurrent_requests = config.concurrent
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# request_id objects for requests which have been slept
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self.sleeping_requests: Set[object] = set()
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# map from request_id object to Deferred for requests which are ready
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# for processing but have been queued
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self.ready_request_queue: collections.OrderedDict[
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object, defer.Deferred[None]
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] = collections.OrderedDict()
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# request id objects for requests which are in progress
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self.current_processing: Set[object] = set()
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# times at which we have recently (within the last window_size ms)
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# received requests.
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self.request_times: List[int] = []
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@contextlib.contextmanager
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def ratelimit(self, host: str) -> "Iterator[defer.Deferred[None]]":
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# `contextlib.contextmanager` takes a generator and turns it into a
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# context manager. The generator should only yield once with a value
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# to be returned by manager.
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# Exceptions will be reraised at the yield.
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self.host = host
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request_id = object()
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# Ideally we'd use `Deferred.fromCoroutine()` here, to save on redundant
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# type-checking, but we'd need Twisted >= 21.2.
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ret = defer.ensureDeferred(self._on_enter_with_tracing(request_id))
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try:
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yield ret
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finally:
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self._on_exit(request_id)
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def should_reject(self) -> bool:
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"""
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Whether to reject the request if we already have too many queued up
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(either sleeping or in the ready queue).
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"""
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queue_size = len(self.ready_request_queue) + len(self.sleeping_requests)
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return queue_size > self.reject_limit
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def should_sleep(self) -> bool:
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"""
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Whether to sleep the request if we already have too many requests coming
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through within the window.
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"""
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return len(self.request_times) > self.sleep_limit
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async def _on_enter_with_tracing(self, request_id: object) -> None:
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maybe_metrics_cm: ContextManager = contextlib.nullcontext()
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if self.metrics_name:
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maybe_metrics_cm = queue_wait_timer.labels(self.metrics_name).time()
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with start_active_span("ratelimit wait"), maybe_metrics_cm:
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await self._on_enter(request_id)
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def _on_enter(self, request_id: object) -> "defer.Deferred[None]":
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time_now = self.clock.time_msec()
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# remove any entries from request_times which aren't within the window
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self.request_times[:] = [
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r for r in self.request_times if time_now - r < self.window_size
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]
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# reject the request if we already have too many queued up (either
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# sleeping or in the ready queue).
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if self.should_reject():
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logger.debug("Ratelimiter(%s): rejecting request", self.host)
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if self.metrics_name:
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rate_limit_reject_counter.labels(self.metrics_name).inc()
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raise LimitExceededError(
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retry_after_ms=int(self.window_size / self.sleep_limit)
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)
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self.request_times.append(time_now)
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def queue_request() -> "defer.Deferred[None]":
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if len(self.current_processing) >= self.concurrent_requests:
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queue_defer: defer.Deferred[None] = defer.Deferred()
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self.ready_request_queue[request_id] = queue_defer
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logger.info(
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"Ratelimiter(%s): queueing request (queue now %i items)",
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self.host,
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len(self.ready_request_queue),
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)
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return queue_defer
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else:
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return defer.succeed(None)
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logger.debug(
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"Ratelimit(%s) [%s]: len(self.request_times)=%d",
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self.host,
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id(request_id),
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len(self.request_times),
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)
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if self.should_sleep():
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logger.debug(
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"Ratelimiter(%s) [%s]: sleeping request for %f sec",
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self.host,
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id(request_id),
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self.sleep_sec,
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)
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if self.metrics_name:
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rate_limit_sleep_counter.labels(self.metrics_name).inc()
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ret_defer = run_in_background(self.clock.sleep, self.sleep_sec)
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self.sleeping_requests.add(request_id)
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def on_wait_finished(_: Any) -> "defer.Deferred[None]":
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logger.debug(
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"Ratelimit(%s) [%s]: Finished sleeping", self.host, id(request_id)
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)
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self.sleeping_requests.discard(request_id)
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queue_defer = queue_request()
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return queue_defer
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ret_defer.addBoth(on_wait_finished)
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else:
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ret_defer = queue_request()
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def on_start(r: object) -> object:
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logger.debug(
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"Ratelimit(%s) [%s]: Processing req", self.host, id(request_id)
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)
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self.current_processing.add(request_id)
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return r
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def on_err(r: object) -> object:
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# XXX: why is this necessary? this is called before we start
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# processing the request so why would the request be in
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# current_processing?
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self.current_processing.discard(request_id)
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return r
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def on_both(r: object) -> object:
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# Ensure that we've properly cleaned up.
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self.sleeping_requests.discard(request_id)
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self.ready_request_queue.pop(request_id, None)
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return r
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ret_defer.addCallbacks(on_start, on_err)
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ret_defer.addBoth(on_both)
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return make_deferred_yieldable(ret_defer)
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def _on_exit(self, request_id: object) -> None:
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logger.debug("Ratelimit(%s) [%s]: Processed req", self.host, id(request_id))
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# When requests complete synchronously, we will recursively start the next
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# request in the queue. To avoid stack exhaustion, we defer starting the next
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# request until the next reactor tick.
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def start_next_request() -> None:
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# We only remove the completed request from the list when we're about to
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# start the next one, otherwise we can allow extra requests through.
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self.current_processing.discard(request_id)
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try:
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# start processing the next item on the queue.
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_, deferred = self.ready_request_queue.popitem(last=False)
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with PreserveLoggingContext():
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deferred.callback(None)
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except KeyError:
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pass
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self.clock.call_later(0.0, start_next_request)
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