1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
|
# -*- coding: utf-8 -*-
# Copyright 2015 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:
_________
---ASa[e]-->| Event |
----ASb[e]->| Grouper |<-poll 1/s--+
--ASa[e]--->|_________| | ASa[e,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.
"""
from twisted.internet import defer
class AppServiceScheduler(object):
""" 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, clock, store, as_api):
self.clock = clock
self.store = store
self.as_api = as_api
self.event_grouper = _EventGrouper()
def create_recoverer(service, callback):
return _Recoverer(clock, store, as_api, service, callback)
self.txn_ctrl = _TransactionController(
clock, store, as_api, self.event_grouper, create_recoverer
)
def start(self):
# check for any DOWN ASes and start recoverers for them.
_Recoverer.start(
self.clock, self.store, self.as_api, self.txn_ctrl.on_recovered
)
self.txn_ctrl.start_polling()
def submit_event_for_as(self, service, event):
self.event_grouper.on_receive(service, event)
class AppServiceTransaction(object):
"""Represents an application service transaction."""
def __init__(self, service, id, events):
self.service = service
self.id = id
self.events = events
def send(self, as_api):
# TODO sends this transaction using this as_api
pass
def complete(self, store):
# TODO increment txn id on AS and nuke txn contents from db
pass
class _EventGrouper(object):
"""Groups events for the same application service together.
"""
def __init__(self):
self.groups = {} # dict of {service: [events]}
def on_receive(self, service, event):
if service not in self.groups:
self.groups[service] = []
self.groups[service].append(event)
def drain_groups(self):
groups = self.groups
self.groups = {}
return groups
class _TransactionController(object):
def __init__(self, clock, store, as_api, event_grouper, recoverer_fn):
self.clock = clock
self.store = store
self.as_api = as_api
self.event_grouper = event_grouper
self.recoverer_fn = recoverer_fn
def start_polling(self):
groups = self.event_grouper.drain_groups()
for service in groups:
txn_id = self._get_next_txn_id(service)
txn = AppServiceTransaction(service, txn_id, groups[service])
self._store_txn(txn)
if self._is_service_up(service):
if txn.send(self.as_api):
txn.complete(self.store)
else:
# TODO mark AS as down
self._start_recoverer(service)
self.clock.call_later(1000, self.start_polling)
def on_recovered(self, service):
# TODO mark AS as UP
pass
def _start_recoverer(self, service):
recoverer = self.recoverer_fn(service, self.on_recovered)
recoverer.recover()
def _is_service_up(self, service):
pass
def _get_next_txn_id(self, service):
pass # TODO work out the next txn_id for this service
def _store_txn(self, txn):
pass
class _Recoverer(object):
@staticmethod
def start(clock, store, as_api, callback):
# TODO check for DOWN ASes and init recoverers
pass
def __init__(self, clock, store, as_api, service, callback):
self.clock = clock
self.store = store
self.as_api = as_api
self.service = service
self.callback = callback
self.backoff_counter = 1
def recover(self):
self.clock.call_later(2000 ** self.backoff_counter, self.retry)
@defer.inlineCallbacks
def retry(self):
txn = yield self._get_oldest_txn()
if txn:
if txn.send(self.as_api):
txn.complete(self.store)
# reset the backoff counter and retry immediately
self.backoff_counter = 1
self.retry()
else:
self.backoff_counter += 1
self.recover()
else:
self._set_service_recovered()
def _set_service_recovered(self):
self.callback(self.service)
@defer.inlineCallbacks
def _get_oldest_txn(self):
txn = yield self.store.get_oldest_txn(self.service)
defer.returnValue(txn)
|
