有时，新的消费群体无效 [英] Sometimes a new consumer group does not work
问题描述
我曾经在生产环境中看到过这种情况（我不记得我们是如何解决的），现在我可以在集成测试中重复进行，集成测试总是从全新的Kafka安装开始。步骤如下：
I've seen this in production once (I don't remember how we solved it) and now I can repeat it in the integration tests, which always start with a brand new Kafka installation. Here's how it goes:
步骤1：尚不存在的组的用户订阅了尚不存在的主题并开始轮询。
Step 1: A consumer of a group that doesn't exist yet subscribes to a topic that does not exist yet and starts polling.
self.kafka_consumer = confluent_kafka.Consumer({
'group.id': 'mygroup',
'bootstrap.servers': 'kafka:9092',
'enable.auto.commit': False,
'auto.offset.reset': 'earliest',
})
self.kafka_consumer.subscribe('mytopic')
第2步：生产者向该主题写消息。
Step 2: A producer writes a message to the topic.
结果：
- 大约可以正常工作的一半；
- 另一半时间，消费者似乎被卡住了。我尝试了长达10分钟的等待时间，看它是否会被卡住，但是不会。
- 即使两个步骤都相反，即消费者尝试订阅已经存在的内容主题已经有消息，行为是相同的（但是组始终是新的）。
更多详细信息
消费者正在以2秒的超时进行轮询，如果没有结果，它将循环。
The consumer is polling with a timeout of 2 seconds, and if there's no result it loops over.
虽然该主题不存在，但 poll（）返回 None 。主题存在后， poll（）返回 msg ，其 error（）。code（ ）是 _PARTITION_EOF 。
While the topic doesn't exist, poll() returns None. After the topic exists, poll() returns an msg whose error().code() is _PARTITION_EOF.
当消费者似乎被卡住时，我问kafka怎么回事在 mygroup 上，它告诉我的是：
While the consumer seems stuck, I ask kafka what's going on with mygroup, and here's what it tells me:
root@e7b124b4039c:/# /usr/local/kafka/bin/kafka-consumer-groups.sh --bootstrap-server localhost:9092 --group mygroup --describe
Note: This will not show information about old Zookeeper-based consumers.
TOPIC PARTITION CURRENT-OFFSET LOG-END-OFFSET LAG CONSUMER-ID HOST CLIENT-ID
root@e7b124b4039c:/#
我试图通过读取另一个不存在的主题，例如 mygroup 来使其不被卡住： p>
I try to make it unstuck by trying to read another nonexistent topic as mygroup:
root@e7b124b4039c:/# /usr/local/kafka/bin/kafka-console-consumer.sh --bootstrap-server localhost:9092 --group mygroup --topic nonexistent --from-beginning
[2018-03-15 16:36:59,369] WARN [Consumer clientId=consumer-1, groupId=pixelprocessor] Error while fetching metadata with correlation id 2 : {nonexistent=LEADER_NOT_AVAILABLE} (org.apache.kafka.clients.NetworkClient)
^CProcessed a total of 0 messages
root@e7b124b4039c:/#
完成之后，这就是卡夫卡对 mygroup 的评价：
After I do that, here's what Kafka has to say about mygroup:
root@e7b124b4039c:/# /usr/local/kafka/bin/kafka-consumer-groups.sh --bootstrap-server localhost:9092 --group mygroup --describe
Note: This will not show information about old Zookeeper-based consumers.
TOPIC PARTITION CURRENT-OFFSET LOG-END-OFFSET LAG CONSUMER-ID HOST CLIENT-ID
mytopic 0 - 1 - rdkafka-a172d013-08e6-4ee2-92f3-fdb07d163d57 /172.20.0.6 rdkafka
(another topic) 0 - 0 - rdkafka-a172d013-08e6-4ee2-92f3-fdb07d163d57 /172.20.0.6 rdkafka
(a third topic) 0 - 0 - rdkafka-a172d013-08e6-4ee2-92f3-fdb07d163d57 /172.20.0.6 rdkafka
nonexistent 0 0 0 0 - - -
这是Kafka 1.0.1，librdkafka 0.11.3，confluent_kafka 0.11.0，在Ubuntu 16.04泊坞窗（带有操作系统的打包的zookeeper 3.4.8）上运行，它们在Linux 4.9.0-6-amd64的Debian扩展版（9.4）上运行。
This is Kafka 1.0.1, librdkafka 0.11.3, confluent_kafka 0.11.0, on Ubuntu 16.04 dockers (with the OS's packaged zookeeper 3.4.8) which are running on a Debian stretch (9.4) with Linux 4.9.0-6-amd64.
推荐答案
问题似乎出在 Consumer（）参数中。这不能正常工作：
The problem seems to have been in the Consumer() arguments. This doesn't work properly:
self.kafka_consumer = confluent_kafka.Consumer({
'group.id': 'mygroup',
'bootstrap.servers': 'kafka:9092',
'auto.offset.reset': 'earliest',
})
但这确实是：
self.kafka_consumer = confluent_kafka.Consumer({
'group.id': 'mygroup',
'bootstrap.servers': 'kafka:9092',
'default.topic.config': {
'auto.offset.reset': 'earliest',
},
})
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