在使用fluentd采集数据到kafka时，一直不通，碰到了很多报错。 fluentd版本为：1.2.5 fluent-plugin-kafka版本为：0.7.8 kafka版本为：0.9 最开始碰到了这个报错：
2018-09-05 01:42:06 +0000 [warn]: fluent/log.rb:342:warn: Send exception occurred: unknown topic
2018-09-05 01:42:06 +0000 [warn]: fluent/log.rb:342:warn: Exception Backtrace : /var/lib/gems/2.3.0/gems/ruby-kafka-0.6.8/lib/kafka/protocol/metadata_response.rb:141:in `partitions_for'
/var/lib/gems/2.3.0/gems/ruby-kafka-0.6.8/lib/kafka/cluster.rb:155:in `partitions_for'
/var/lib/gems/2.3.0/gems/fluent-plugin-kafka-0.7.6/lib/fluent/plugin/kafka_producer_ext.rb:190:in `assign_partitions!'
/var/lib/gems/2.3.0/gems/fluent-plugin-kafka-0.7.6/lib/fluent/plugin/kafka_producer_ext.rb:153:in `block in deliver_messages_with_retries'
/var/lib/gems/2.3.0/gems/fluent-plugin-kafka-0.7.6/lib/fluent/plugin/kafka_producer_ext.rb:148:in `loop'
/var/lib/gems/2.3.0/gems/fluent-plugin-kafka-0.7.6/lib/fluent/plugin/kafka_producer_ext.rb:148:in `deliver_messages_with_retries'
/var/lib/gems/2.3.0/gems/fluent-plugin-kafka-0.7.6/lib/fluent/plugin/kafka_producer_ext.rb:102:in `deliver_messages'
/var/lib/gems/2.3.0/gems/fluent-plugin-kafka-0.7.6/lib/fluent/plugin/out_kafka2.rb:220:in `write'
/var/lib/gems/2.3.0/gems/fluentd-1.2.4/lib/fluent/plugin/output.rb:1110:in `try_flush'
/var/lib/gems/2.3.0/gems/fluentd-1.2.4/lib/fluent/plugin/output.rb:1389:in `flush_thread_run'
/var/lib/gems/2.3.0/gems/fluentd-1.2.4/lib/fluent/plugin/output.rb:444:in `block (2 levels) in start'
/var/lib/gems/2.3.0/gems/fluentd-1.2.4/lib/fluent/plugin_helper/thread.rb:78:in `block in thread_create'
2018-09-05 01:42:06 +0000 [info]: fluent/log.rb:322:info: initialized kafka producer: fluentd
2018-09-05 01:42:06 +0000 [debug]: fluent/log.rb:302:debug: taking back chunk for errors. chunk="57515e0ef787da843836cc864f9d1581"
2018-09-05 01:42:06 +0000 [warn]: fluent/log.rb:342:warn: failed to flush the buffer. retry_time=2 next_retry_seconds=2018-09-05 01:42:06 +0000 chunk="57515e0ef787da843836cc864f9d1581" error_class=Kafka::UnknownTopicOrPartition error="unknown topic "
2018-09-05 01:42:06 +0000 [warn]: plugin/output.rb:1157:rescue in try_flush: suppressed same stacktrace
2018-09-05 01:42:09 +0000 [debug]: fluent/log.rb:302:debug: 61 messages send.
2018-09-05 01:42:09 +0000 [warn]: fluent/log.rb:342:warn: Send exception occurred: unknown topic
2018-09-05 01:42:09 +0000 [warn]: fluent/log.rb:342:warn: Exception Backtrace : /var/lib/gems/2.3.0/gems/ruby-kafka-0.6.8/lib/kafka/protocol/metadata_response.rb:141:in `partitions_for'
/var/lib/gems/2.3.0/gems/ruby-kafka-0.6.8/lib/kafka/cluster.rb:155:in `partitions_for'
/var/lib/gems/2.3.0/gems/fluent-plugin-kafka-0.7.6/lib/fluent/plugin/kafka_producer_ext.rb:190:in `assign_partitions!'
/var/lib/gems/2.3.0/gems/fluent-plugin-kafka-0.7.6/lib/fluent/plugin/kafka_producer_ext.rb:153:in `block in deliver_messages_with_retries'
/var/lib/gems/2.3.0/gems/fluent-plugin-kafka-0.7.6/lib/fluent/plugin/kafka_producer_ext.rb:148:in `loop'
/var/lib/gems/2.3.0/gems/fluent-plugin-kafka-0.7.6/lib/fluent/plugin/kafka_producer_ext.rb:148:in `deliver_messages_with_retries'
/var/lib/gems/2.3.0/gems/fluent-plugin-kafka-0.7.6/lib/fluent/plugin/kafka_producer_ext.rb:102:in `deliver_messages'
/var/lib/gems/2.3.0/gems/fluent-plugin-kafka-0.7.6/lib/fluent/plugin/out_kafka2.rb:220:in `write'
/var/lib/gems/2.3.0/gems/fluentd-1.2.4/lib/fluent/plugin/output.rb:1110:in `try_flush'
/var/lib/gems/2.3.0/gems/fluentd-1.2.4/lib/fluent/plugin/output.rb:1389:in `flush_thread_run'
/var/lib/gems/2.3.0/gems/fluentd-1.2.4/lib/fluent/plugin/output.rb:444:in `block (2 levels) in start'
/var/lib/gems/2.3.0/gems/fluentd-1.2.4/lib/fluent/plugin_helper/thread.rb:78:in `block in thread_create'
2018-09-05 01:42:09 +0000 [info]: fluent/log.rb:322:info: initialized kafka producer: fluentd
2018-09-05 01:42:09 +0000 [debug]: fluent/log.rb:302:debug: taking back chunk for errors. chunk="57515e0ef787da843836cc864f9d1581"
2018-09-05 01:42:09 +0000 [warn]: fluent/log.rb:342:warn: failed to flush the buffer. retry_time=3 next_retry_seconds=2018-09-05 01:42:09 +0000
这是因为没有配置default_topic,使用下面的配置指定topic就可以了。
