forked from MirrorHub/synapse
Rip out the DNS lookup limiter (#10190)
As I've written in various places in the past (#7113, #9865) I'm pretty sure this is doing nothing useful at all.
This commit is contained in:
Richard van der Hoff
GitHub
parent
8070b893db
commit
9cf6e0eae7
2 changed files with 1 additions and 104 deletions
1
changelog.d/10190.misc
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1
changelog.d/10190.misc
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Remove redundant DNS lookup limiter.
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@ -38,7 +38,6 @@ from synapse.crypto import context_factory
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from synapse.logging.context import PreserveLoggingContext
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from synapse.logging.context import PreserveLoggingContext
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from synapse.metrics.background_process_metrics import wrap_as_background_process
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from synapse.metrics.background_process_metrics import wrap_as_background_process
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from synapse.metrics.jemalloc import setup_jemalloc_stats
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from synapse.metrics.jemalloc import setup_jemalloc_stats
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from synapse.util.async_helpers import Linearizer
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from synapse.util.daemonize import daemonize_process
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from synapse.util.daemonize import daemonize_process
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from synapse.util.rlimit import change_resource_limit
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from synapse.util.rlimit import change_resource_limit
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from synapse.util.versionstring import get_version_string
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from synapse.util.versionstring import get_version_string
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@ -112,8 +111,6 @@ def start_reactor(
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run_command (Callable[]): callable that actually runs the reactor
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run_command (Callable[]): callable that actually runs the reactor
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"""
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"""
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install_dns_limiter(reactor)
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def run():
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def run():
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logger.info("Running")
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logger.info("Running")
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setup_jemalloc_stats()
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setup_jemalloc_stats()
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@ -398,107 +395,6 @@ def setup_sdnotify(hs):
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)
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)
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def install_dns_limiter(reactor, max_dns_requests_in_flight=100):
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"""Replaces the resolver with one that limits the number of in flight DNS
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requests.
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This is to workaround https://twistedmatrix.com/trac/ticket/9620, where we
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can run out of file descriptors and infinite loop if we attempt to do too
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many DNS queries at once
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XXX: I'm confused by this. reactor.nameResolver does not use twisted.names unless
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you explicitly install twisted.names as the resolver; rather it uses a GAIResolver
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backed by the reactor's default threadpool (which is limited to 10 threads). So
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(a) I don't understand why twisted ticket 9620 is relevant, and (b) I don't
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understand why we would run out of FDs if we did too many lookups at once.
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-- richvdh 2020/08/29
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"""
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new_resolver = _LimitedHostnameResolver(
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reactor.nameResolver, max_dns_requests_in_flight
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)
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reactor.installNameResolver(new_resolver)
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class _LimitedHostnameResolver:
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"""Wraps a IHostnameResolver, limiting the number of in-flight DNS lookups."""
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def __init__(self, resolver, max_dns_requests_in_flight):
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self._resolver = resolver
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self._limiter = Linearizer(
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name="dns_client_limiter", max_count=max_dns_requests_in_flight
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)
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def resolveHostName(
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self,
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resolutionReceiver,
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hostName,
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portNumber=0,
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addressTypes=None,
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transportSemantics="TCP",
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):
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# We need this function to return `resolutionReceiver` so we do all the
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# actual logic involving deferreds in a separate function.
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# even though this is happening within the depths of twisted, we need to drop
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# our logcontext before starting _resolve, otherwise: (a) _resolve will drop
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# the logcontext if it returns an incomplete deferred; (b) _resolve will
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# call the resolutionReceiver *with* a logcontext, which it won't be expecting.
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with PreserveLoggingContext():
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self._resolve(
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resolutionReceiver,
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hostName,
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portNumber,
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addressTypes,
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transportSemantics,
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)
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return resolutionReceiver
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@defer.inlineCallbacks
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def _resolve(
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self,
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resolutionReceiver,
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hostName,
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portNumber=0,
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addressTypes=None,
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transportSemantics="TCP",
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):
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with (yield self._limiter.queue(())):
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# resolveHostName doesn't return a Deferred, so we need to hook into
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# the receiver interface to get told when resolution has finished.
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deferred = defer.Deferred()
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receiver = _DeferredResolutionReceiver(resolutionReceiver, deferred)
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self._resolver.resolveHostName(
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receiver, hostName, portNumber, addressTypes, transportSemantics
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)
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yield deferred
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class _DeferredResolutionReceiver:
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"""Wraps a IResolutionReceiver and simply resolves the given deferred when
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resolution is complete
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"""
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def __init__(self, receiver, deferred):
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self._receiver = receiver
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self._deferred = deferred
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def resolutionBegan(self, resolutionInProgress):
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self._receiver.resolutionBegan(resolutionInProgress)
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def addressResolved(self, address):
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self._receiver.addressResolved(address)
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def resolutionComplete(self):
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self._deferred.callback(())
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self._receiver.resolutionComplete()
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sdnotify_sockaddr = os.getenv("NOTIFY_SOCKET")
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sdnotify_sockaddr = os.getenv("NOTIFY_SOCKET")
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