# 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. """ This module controls the reliability for application service transactions. The nominal flow through this module looks like: __________ 1---ASa[e]-->| Service |--> Queue ASa[f] 2----ASb[e]->| Queuer | 3--ASa[f]--->|__________|-----------+ ASa[e], ASb[e] V -````````- +------------+ |````````|<--StoreTxn-|Transaction | |Database| | Controller |---> SEND TO AS `--------` +------------+ What happens on SEND TO AS depends on the state of the Application Service: - If the AS is marked as DOWN, do nothing. - If the AS is marked as UP, send the transaction. * SUCCESS : Increment where the AS is up to txn-wise and nuke the txn contents from the db. * FAILURE : Marked AS as DOWN and start Recoverer. Recoverer attempts to recover ASes who have died. The flow for this looks like: ,--------------------- backoff++ --------------. V | START ---> Wait exp ------> Get oldest txn ID from ----> FAILURE backoff DB and try to send it ^ |___________ Mark AS as | V UP & quit +---------- YES SUCCESS | | | NO <--- Have more txns? <------ Mark txn success & nuke <-+ from db; incr AS pos. Reset backoff. This is all tied together by the AppServiceScheduler which DIs the required components. """ import logging from typing import ( TYPE_CHECKING, Awaitable, Callable, Collection, Dict, List, Optional, Set, ) from synapse.appservice import ApplicationService, ApplicationServiceState from synapse.appservice.api import ApplicationServiceApi from synapse.events import EventBase from synapse.logging.context import run_in_background from synapse.metrics.background_process_metrics import run_as_background_process from synapse.storage.databases.main import DataStore from synapse.types import JsonDict from synapse.util import Clock if TYPE_CHECKING: from synapse.server import HomeServer logger = logging.getLogger(__name__) # Maximum number of events to provide in an AS transaction. MAX_PERSISTENT_EVENTS_PER_TRANSACTION = 100 # Maximum number of ephemeral events to provide in an AS transaction. MAX_EPHEMERAL_EVENTS_PER_TRANSACTION = 100 # Maximum number of to-device messages to provide in an AS transaction. MAX_TO_DEVICE_MESSAGES_PER_TRANSACTION = 100 class ApplicationServiceScheduler: """Public facing API for this module. Does the required DI to tie the components together. This also serves as the "event_pool", which in this case is a simple array. """ def __init__(self, hs: "HomeServer"): self.clock = hs.get_clock() self.store = hs.get_datastore() self.as_api = hs.get_application_service_api() self.txn_ctrl = _TransactionController(self.clock, self.store, self.as_api) self.queuer = _ServiceQueuer(self.txn_ctrl, self.clock) async def start(self) -> None: logger.info("Starting appservice scheduler") # check for any DOWN ASes and start recoverers for them. services = await self.store.get_appservices_by_state( ApplicationServiceState.DOWN ) for service in services: self.txn_ctrl.start_recoverer(service) def enqueue_for_appservice( self, appservice: ApplicationService, events: Optional[Collection[EventBase]] = None, ephemeral: Optional[Collection[JsonDict]] = None, to_device_messages: Optional[Collection[JsonDict]] = None, ) -> None: """ Enqueue some data to be sent off to an application service. Args: appservice: The application service to create and send a transaction to. events: The persistent room events to send. ephemeral: The ephemeral events to send. to_device_messages: The to-device messages to send. These differ from normal to-device messages sent to clients, as they have 'to_device_id' and 'to_user_id' fields. """ # We purposefully allow this method to run with empty events/ephemeral # collections, so that callers do not need to check iterable size themselves. if not events and not ephemeral and not to_device_messages: return if events: self.queuer.queued_events.setdefault(appservice.id, []).extend(events) if ephemeral: self.queuer.queued_ephemeral.setdefault(appservice.id, []).extend(ephemeral) if to_device_messages: self.queuer.queued_to_device_messages.setdefault(appservice.id, []).extend( to_device_messages ) # Kick off a new application service transaction self.queuer.start_background_request(appservice) class _ServiceQueuer: """Queue of events waiting to be sent to appservices. Groups events into transactions per-appservice, and sends them on to the TransactionController. Makes sure that we only have one transaction in flight per appservice at a given time. """ def __init__(self, txn_ctrl: "_TransactionController", clock: Clock): # dict of {service_id: [events]} self.queued_events: Dict[str, List[EventBase]] = {} # dict of {service_id: [events]} self.queued_ephemeral: Dict[str, List[JsonDict]] = {} # dict of {service_id: [to_device_message_json]} self.queued_to_device_messages: Dict[str, List[JsonDict]] = {} # the appservices which currently have a transaction in flight self.requests_in_flight: Set[str] = set() self.txn_ctrl = txn_ctrl self.clock = clock def start_background_request(self, service: ApplicationService) -> None: # start a sender for this appservice if we don't already have one if service.id in self.requests_in_flight: return run_as_background_process( "as-sender-%s" % (service.id,), self._send_request, service ) async def _send_request(self, service: ApplicationService) -> None: # sanity-check: we shouldn't get here if this service already has a sender # running. assert service.id not in self.requests_in_flight self.requests_in_flight.add(service.id) try: while True: all_events = self.queued_events.get(service.id, []) events = all_events[:MAX_PERSISTENT_EVENTS_PER_TRANSACTION] del all_events[:MAX_PERSISTENT_EVENTS_PER_TRANSACTION] all_events_ephemeral = self.queued_ephemeral.get(service.id, []) ephemeral = all_events_ephemeral[:MAX_EPHEMERAL_EVENTS_PER_TRANSACTION] del all_events_ephemeral[:MAX_EPHEMERAL_EVENTS_PER_TRANSACTION] all_to_device_messages = self.queued_to_device_messages.get( service.id, [] ) to_device_messages_to_send = all_to_device_messages[ :MAX_TO_DEVICE_MESSAGES_PER_TRANSACTION ] del all_to_device_messages[:MAX_TO_DEVICE_MESSAGES_PER_TRANSACTION] if not events and not ephemeral and not to_device_messages_to_send: return try: await self.txn_ctrl.send( service, events, ephemeral, to_device_messages_to_send ) except Exception: logger.exception("AS request failed") finally: self.requests_in_flight.discard(service.id) class _TransactionController: """Transaction manager. Builds AppServiceTransactions and runs their lifecycle. Also starts a Recoverer if a transaction fails. (Note we have only have one of these in the homeserver.) """ def __init__(self, clock: Clock, store: DataStore, as_api: ApplicationServiceApi): self.clock = clock self.store = store self.as_api = as_api # map from service id to recoverer instance self.recoverers: Dict[str, "_Recoverer"] = {} # for UTs self.RECOVERER_CLASS = _Recoverer async def send( self, service: ApplicationService, events: List[EventBase], ephemeral: Optional[List[JsonDict]] = None, to_device_messages: Optional[List[JsonDict]] = None, ) -> None: """ Create a transaction with the given data and send to the provided application service. Args: service: The application service to send the transaction to. events: The persistent events to include in the transaction. ephemeral: The ephemeral events to include in the transaction. to_device_messages: The to-device messages to include in the transaction. """ try: txn = await self.store.create_appservice_txn( service=service, events=events, ephemeral=ephemeral or [], to_device_messages=to_device_messages or [], ) service_is_up = await self._is_service_up(service) if service_is_up: sent = await txn.send(self.as_api) if sent: await txn.complete(self.store) else: run_in_background(self._on_txn_fail, service) except Exception: logger.exception("Error creating appservice transaction") run_in_background(self._on_txn_fail, service) async def on_recovered(self, recoverer: "_Recoverer") -> None: logger.info( "Successfully recovered application service AS ID %s", recoverer.service.id ) self.recoverers.pop(recoverer.service.id) logger.info("Remaining active recoverers: %s", len(self.recoverers)) await self.store.set_appservice_state( recoverer.service, ApplicationServiceState.UP ) async def _on_txn_fail(self, service: ApplicationService) -> None: try: await self.store.set_appservice_state(service, ApplicationServiceState.DOWN) self.start_recoverer(service) except Exception: logger.exception("Error starting AS recoverer") def start_recoverer(self, service: ApplicationService) -> None: """Start a Recoverer for the given service Args: service: """ logger.info("Starting recoverer for AS ID %s", service.id) assert service.id not in self.recoverers recoverer = self.RECOVERER_CLASS( self.clock, self.store, self.as_api, service, self.on_recovered ) self.recoverers[service.id] = recoverer recoverer.recover() logger.info("Now %i active recoverers", len(self.recoverers)) async def _is_service_up(self, service: ApplicationService) -> bool: state = await self.store.get_appservice_state(service) return state == ApplicationServiceState.UP or state is None class _Recoverer: """Manages retries and backoff for a DOWN appservice. We have one of these for each appservice which is currently considered DOWN. Args: clock (synapse.util.Clock): store (synapse.storage.DataStore): as_api (synapse.appservice.api.ApplicationServiceApi): service (synapse.appservice.ApplicationService): the service we are managing callback (callable[_Recoverer]): called once the service recovers. """ def __init__( self, clock: Clock, store: DataStore, as_api: ApplicationServiceApi, service: ApplicationService, callback: Callable[["_Recoverer"], Awaitable[None]], ): self.clock = clock self.store = store self.as_api = as_api self.service = service self.callback = callback self.backoff_counter = 1 def recover(self) -> None: def _retry() -> None: run_as_background_process( "as-recoverer-%s" % (self.service.id,), self.retry ) delay = 2 ** self.backoff_counter logger.info("Scheduling retries on %s in %fs", self.service.id, delay) self.clock.call_later(delay, _retry) def _backoff(self) -> None: # cap the backoff to be around 8.5min => (2^9) = 512 secs if self.backoff_counter < 9: self.backoff_counter += 1 self.recover() async def retry(self) -> None: logger.info("Starting retries on %s", self.service.id) try: while True: txn = await self.store.get_oldest_unsent_txn(self.service) if not txn: # nothing left: we're done! await self.callback(self) return logger.info( "Retrying transaction %s for AS ID %s", txn.id, txn.service.id ) sent = await txn.send(self.as_api) if not sent: break await txn.complete(self.store) # reset the backoff counter and then process the next transaction self.backoff_counter = 1 except Exception: logger.exception("Unexpected error running retries") # we didn't manage to send all of the transactions before we got an error of # some flavour: reschedule the next retry. self._backoff()