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# Copyright 2015, 2016 OpenMarket Ltd
#
# 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 random
import synapse.logging.context
from synapse.api.errors import CodeMessageException
logger = logging.getLogger(__name__)
# the initial backoff, after the first transaction fails
MIN_RETRY_INTERVAL = 10 * 60 * 1000
# how much we multiply the backoff by after each subsequent fail
RETRY_MULTIPLIER = 5
# a cap on the backoff. (Essentially none)
MAX_RETRY_INTERVAL = 2 ** 62
class NotRetryingDestination(Exception):
def __init__(self, retry_last_ts, retry_interval, destination):
"""Raised by the limiter (and federation client) to indicate that we are
are deliberately not attempting to contact a given server.
Args:
retry_last_ts (int): the unix ts in milliseconds of our last attempt
to contact the server. 0 indicates that the last attempt was
successful or that we've never actually attempted to connect.
retry_interval (int): the time in milliseconds to wait until the next
attempt.
destination (str): the domain in question
"""
msg = "Not retrying server %s." % (destination,)
super().__init__(msg)
self.retry_last_ts = retry_last_ts
self.retry_interval = retry_interval
self.destination = destination
async def get_retry_limiter(destination, clock, store, ignore_backoff=False, **kwargs):
"""For a given destination check if we have previously failed to
send a request there and are waiting before retrying the destination.
If we are not ready to retry the destination, this will raise a
NotRetryingDestination exception. Otherwise, will return a Context Manager
that will mark the destination as down if an exception is thrown (excluding
CodeMessageException with code < 500)
Args:
destination (str): name of homeserver
clock (synapse.util.clock): timing source
store (synapse.storage.transactions.TransactionStore): datastore
ignore_backoff (bool): true to ignore the historical backoff data and
try the request anyway. We will still reset the retry_interval on success.
Example usage:
try:
limiter = await get_retry_limiter(destination, clock, store)
with limiter:
response = await do_request()
except NotRetryingDestination:
# We aren't ready to retry that destination.
raise
"""
failure_ts = None
retry_last_ts, retry_interval = (0, 0)
retry_timings = await store.get_destination_retry_timings(destination)
if retry_timings:
failure_ts = retry_timings.failure_ts
retry_last_ts = retry_timings.retry_last_ts
retry_interval = retry_timings.retry_interval
now = int(clock.time_msec())
if not ignore_backoff and retry_last_ts + retry_interval > now:
raise NotRetryingDestination(
retry_last_ts=retry_last_ts,
retry_interval=retry_interval,
destination=destination,
)
# if we are ignoring the backoff data, we should also not increment the backoff
# when we get another failure - otherwise a server can very quickly reach the
# maximum backoff even though it might only have been down briefly
backoff_on_failure = not ignore_backoff
return RetryDestinationLimiter(
destination,
clock,
store,
failure_ts,
retry_interval,
backoff_on_failure=backoff_on_failure,
**kwargs,
)
class RetryDestinationLimiter:
def __init__(
self,
destination,
clock,
store,
failure_ts,
retry_interval,
backoff_on_404=False,
backoff_on_failure=True,
):
"""Marks the destination as "down" if an exception is thrown in the
context, except for CodeMessageException with code < 500.
If no exception is raised, marks the destination as "up".
Args:
destination (str)
clock (Clock)
store (DataStore)
failure_ts (int|None): when this destination started failing (in ms since
the epoch), or zero if the last request was successful
retry_interval (int): The next retry interval taken from the
database in milliseconds, or zero if the last request was
successful.
backoff_on_404 (bool): Back off if we get a 404
backoff_on_failure (bool): set to False if we should not increase the
retry interval on a failure.
"""
self.clock = clock
self.store = store
self.destination = destination
self.failure_ts = failure_ts
self.retry_interval = retry_interval
self.backoff_on_404 = backoff_on_404
self.backoff_on_failure = backoff_on_failure
def __enter__(self):
pass
def __exit__(self, exc_type, exc_val, exc_tb):
valid_err_code = False
if exc_type is None:
valid_err_code = True
elif not issubclass(exc_type, Exception):
# avoid treating exceptions which don't derive from Exception as
# failures; this is mostly so as not to catch defer._DefGen.
valid_err_code = True
elif issubclass(exc_type, CodeMessageException):
# Some error codes are perfectly fine for some APIs, whereas other
# APIs may expect to never received e.g. a 404. It's important to
# handle 404 as some remote servers will return a 404 when the HS
# has been decommissioned.
# If we get a 401, then we should probably back off since they
# won't accept our requests for at least a while.
# 429 is us being aggressively rate limited, so lets rate limit
# ourselves.
if exc_val.code == 404 and self.backoff_on_404:
valid_err_code = False
elif exc_val.code in (401, 429):
valid_err_code = False
elif exc_val.code < 500:
valid_err_code = True
else:
valid_err_code = False
if valid_err_code:
# We connected successfully.
if not self.retry_interval:
return
logger.debug(
"Connection to %s was successful; clearing backoff", self.destination
)
self.failure_ts = None
retry_last_ts = 0
self.retry_interval = 0
elif not self.backoff_on_failure:
return
else:
# We couldn't connect.
if self.retry_interval:
self.retry_interval = int(
self.retry_interval * RETRY_MULTIPLIER * random.uniform(0.8, 1.4)
)
if self.retry_interval >= MAX_RETRY_INTERVAL:
self.retry_interval = MAX_RETRY_INTERVAL
else:
self.retry_interval = MIN_RETRY_INTERVAL
logger.info(
"Connection to %s was unsuccessful (%s(%s)); backoff now %i",
self.destination,
exc_type,
exc_val,
self.retry_interval,
)
retry_last_ts = int(self.clock.time_msec())
if self.failure_ts is None:
self.failure_ts = retry_last_ts
async def store_retry_timings():
try:
await self.store.set_destination_retry_timings(
self.destination,
self.failure_ts,
retry_last_ts,
self.retry_interval,
)
except Exception:
logger.exception("Failed to store destination_retry_timings")
# we deliberately do this in the background.
synapse.logging.context.run_in_background(store_retry_timings)
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