確認后 GCP 消息保留在 Pub/Sub 中

Question

我將 Pub/Sub 訂閱邏輯包裝在一個訂閱方法中，該方法在每個訂閱的服務初始化期間調用一次：

    def subscribe(self,
                  callback: typing.Callable,
                  subscription_name: str,
                  topic_name: str,
                  project_name: str = None) -> typing.Optional[SubscriberClient]:
        """Subscribes to Pub/Sub topic and return subscriber client

        :param callback: subscription callback method
        :param subscription_name: name of the subscription
        :param topic_name: name of the topic
        :param project_name: optional project name. Uses default project if not set
        :return: subscriber client or None if testing
        """
        project = project_name if project_name else self.pubsub_project_id
        self.logger.info('Subscribing to project `{}`, topic `{}`'.format(project, topic_name))

        project_path = self.pubsub_subscriber.project_path(project)
        topic_path = self.pubsub_subscriber.topic_path(project, topic_name)
        subscription_path = self.pubsub_subscriber.subscription_path(project, subscription_name)

        # check if there is an existing subscription, if not, create it
        if subscription_path not in [s.name for s in self.pubsub_subscriber.list_subscriptions(project_path)]:
            self.logger.info('Creating new subscription `{}`, topic `{}`'.format(subscription_name, topic_name))
            self.pubsub_subscriber.create_subscription(subscription_path, topic_path)

        # subscribe to the topic
        self.pubsub_subscriber.subscribe(
            subscription_path, callback=callback,
            scheduler=self.thread_scheduler
        )
        return self.pubsub_subscriber

這個方法是這樣調用的：

        self.subscribe_client = self.subscribe(
            callback=self.pubsub_callback,
            subscription_name='subscription_topic',
            topic_name='topic'
        )

回調方法做了很多事情，發送 2 封電子郵件，然后確認消息

    def pubsub_callback(self, data: gcloud_pubsub_subscriber.Message):
        self.logger.debug('Processing pub sub message')

        try:
            self.do_something_with_message(data)

            self.logger.debug('Acknowledging the message')
            data.ack()
            self.logger.debug('Acknowledged')
            return

        except:
            self.logger.warning({
                "message": "Failed to process Pub/Sub message",
                "request_size": data.size,
                "data": data.data
            }, exc_info=True)

        self.logger.debug('Acknowledging the message 2')
        data.ack()

當我向訂閱運行推送某些內容時，回調運行，打印所有調試消息，包括Acknowledged 。 但是，消息保留在 Pub/Sub 中，回調被再次調用，並且每次重試后都需要指數級的時間。 問題是，即使在調用ack之后，什么可能導致消息保留在 pub/sub 中？

我有幾個這樣的訂閱，它們都按預期工作。 截止日期不是一個選項，回調幾乎立即完成，無論如何我都玩了確認截止日期，沒有任何幫助。

當我嘗試從連接到該 pub-sub 的本地運行的應用程序處理這些消息時，它完成得很好，並且確認按預期將消息從隊列中取出。

• 所以問題只在部署的服務中表現出來（在 kubernetes pod 內運行）
• 回調執行 buck ack 似乎什么都不做
• 來自本地運行的腳本（...並執行完全相同的操作）或通過 GCP UI 的確認消息按預期工作。

有任何想法嗎？

Answer 1

確認是 Pub/Sub 中的最大努力，因此重新傳遞消息是可能的，但不常見。

如果您一直收到重復消息，則可能是由於相同消息內容的重復發布。 就 Pub/Sub 而言，這些是不同的消息，將被分配不同的消息 ID。 檢查 Pub/Sub 提供的消息 ID，以確保您實際上多次收到相同的消息。

使用流式拉取處理大量積壓的小消息有一個極端情況（這是 Python 客戶端庫使用的）。 如果您正在運行多個訂閱同一訂閱的客戶端，則此邊緣情況可能是相關的。

您還可以檢查訂閱的Stackdriver 指標以查看：

• 如果它的確認發送成功（ subscription/ack_message_count ）
• 如果它的積壓正在減少（ subscription/backlog_bytes積壓字節）
• 如果您的訂閱者錯過了確認截止日期（通過 response_code 過濾的subscription/streaming_pull_ack_message_operation_count response_code != "success" ）

如果您沒有錯過確認截止日期並且您的積壓工作保持穩定，您應該聯系 Google Cloud 支持並提供您的項目名稱、訂閱名稱和重復消息 ID 的示例。 他們將能夠調查為什么會發生這些重復。

Answer 2

我做了一些額外的測試，終於找到了問題所在。

TL;DR：我對所有訂閱都使用相同的google.cloud.pubsub_v1.subscriber.scheduler.ThreadScheduler 。

這是我用來測試它的代碼片段。 這是損壞的版本：

服務器.py

import concurrent.futures.thread
import os
import time

from google.api_core.exceptions import AlreadyExists
from google.cloud import pubsub_v1
from google.cloud.pubsub_v1.subscriber.scheduler import ThreadScheduler


def create_subscription(project_id, topic_name, subscription_name):
    """Create a new pull subscription on the given topic."""
    subscriber = pubsub_v1.SubscriberClient()
    topic_path = subscriber.topic_path(project_id, topic_name)
    subscription_path = subscriber.subscription_path(
        project_id, subscription_name)

    subscription = subscriber.create_subscription(
        subscription_path, topic_path)

    print('Subscription created: {}'.format(subscription))


def receive_messages(project_id, subscription_name, t_scheduler):
    """Receives messages from a pull subscription."""
    subscriber = pubsub_v1.SubscriberClient()
    subscription_path = subscriber.subscription_path(
        project_id, subscription_name)

    def callback(message):
        print('Received message: {}'.format(message.data))
        message.ack()

    subscriber.subscribe(subscription_path, callback=callback, scheduler=t_scheduler)
    print('Listening for messages on {}'.format(subscription_path))


project_id = os.getenv("PUBSUB_PROJECT_ID")

publisher = pubsub_v1.PublisherClient()
project_path = publisher.project_path(project_id)

# Create both topics
try:
    topics = [topic.name.split('/')[-1] for topic in publisher.list_topics(project_path)]
    if 'topic_a' not in topics:
        publisher.create_topic(publisher.topic_path(project_id, 'topic_a'))
    if 'topic_b' not in topics:
        publisher.create_topic(publisher.topic_path(project_id, 'topic_b'))
except AlreadyExists:
    print('Topics already exists')

# Create subscriptions on both topics
sub_client = pubsub_v1.SubscriberClient()
project_path = sub_client.project_path(project_id)

try:
    subs = [sub.name.split('/')[-1] for sub in sub_client.list_subscriptions(project_path)]
    if 'topic_a_sub' not in subs:
        create_subscription(project_id, 'topic_a', 'topic_a_sub')
    if 'topic_b_sub' not in subs:
        create_subscription(project_id, 'topic_b', 'topic_b_sub')
except AlreadyExists:
    print('Subscriptions already exists')

scheduler = ThreadScheduler(concurrent.futures.thread.ThreadPoolExecutor(10))

receive_messages(project_id, 'topic_a_sub', scheduler)
receive_messages(project_id, 'topic_b_sub', scheduler)

while True:
    time.sleep(60)

客戶端.py

import datetime
import os
import random
import sys
from time import sleep

from google.cloud import pubsub_v1


def publish_messages(pid, topic_name):
    """Publishes multiple messages to a Pub/Sub topic."""
    publisher = pubsub_v1.PublisherClient()
    topic_path = publisher.topic_path(pid, topic_name)

    for n in range(1, 10):
        data = '[{} - {}] Message number {}'.format(datetime.datetime.now().isoformat(), topic_name, n)
        data = data.encode('utf-8')
        publisher.publish(topic_path, data=data)
        sleep(random.randint(10, 50) / 10.0)


project_id = os.getenv("PUBSUB_PROJECT_ID")
publish_messages(project_id, sys.argv[1])

我連接到雲發布/訂閱，服務器創建主題和訂閱。 然后我為這兩個主題並行運行了多次客戶端腳本。 過了一會兒，一旦我更改服務器代碼以在receive_messages scope 中實例化新的線程調度程序，服務器清理了兩個主題並按預期運行。

令人困惑的是，無論哪種情況，服務器都會打印出所有消息的接收消息。

我將把這個發布到https://github.com/googleapis/google-cloud-python/issues