背景
初学filebeat和logstash，于是根据官方文档，做了个最简单的filebeat采集日志，然后输出到logstash的最简配置。本以为可以愉快的输出“helloworld”的…
问题
启动配置好的filebeat和logstash，正想见证奇迹的时刻，没想到logstash启动完之后，紧接着给我来个当头棒喝，抛了下面一个很长的异常：
io.netty.handler.codec.DecoderException: org.logstash.beats.BeatsParser$InvalidFrameProtocolException: Invalid Frame Type, received: 69
at io.netty.handler.codec.ByteToMessageDecoder.callDecode(ByteToMessageDecoder.java:472) ~[netty-all-4.1.30.Final.jar:4.1.30.Final]
at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:278) ~[netty-all-4.1.30.Final.jar:4.1.30.Final]
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:362) ~[netty-all-4.1.30.Final.jar:4.1.30.Final]
at io.netty.channel.AbstractChannelHandlerContext.access$600(AbstractChannelHandlerContext.java:38) ~[netty-all-4.1.30.Final.jar:4.1.30.Final]
at io.netty.channel.AbstractChannelHandlerContext$7.run(AbstractChannelHandlerContext.java:353) ~[netty-all-4.1.30.Final.jar:4.1.30.Final]
at io.netty.util.concurrent.DefaultEventExecutor.run(DefaultEventExecutor.java:66) ~[netty-all-4.1.30.Final.jar:4.1.30.Final]
at io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:897) [netty-all-4.1.30.Final.jar:4.1.30.Final]
at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30) [netty-all-4.1.30.Final.jar:4.1.30.Final]
at java.lang.Thread.run(Thread.java:834) [?:?]
Caused by: org.logstash.beats.BeatsParser$InvalidFrameProtocolException: Invalid Frame Type, received: 69
at org.logstash.beats.BeatsParser.decode(BeatsParser.java:92) ~[logstash-input-beats-6.0.0.jar:?]
at io.netty.handler.codec.ByteToMessageDecoder.decodeRemovalReentryProtection(ByteToMessageDecoder.java:502) ~[netty-all-4.1.30.Final.jar:4.1.30.Final]
at io.netty.handler.codec.ByteToMessageDecoder.callDecode(ByteToMessageDecoder.java:441) ~[netty-all-4.1.30.Final.jar:4.1.30.Final]
... 8 more
////////////////////////////此处省略一些异常////////////////////////////////////
[INFO ] 2020-03-03 10:39:29.943 [defaultEventExecutorGroup-4-1] BeatsHandler - [local: 127.0.0.1:5044, remote: 127.0.0.1:44356] Handling exception: org.logstash.beats.BeatsParser$InvalidFrameProtocolException: Invalid Frame Type, received: 84
[WARN ] 2020-03-03 10:39:29.943 [nioEventLoopGroup-2-2] DefaultChannelPipeline - An exceptionCaught() event was fired, and it reached at the tail of the pipeline. It usually means the last handler in the pipeline did not handle the exception.
io.netty.handler.codec.DecoderException: org.logstash.beats.BeatsParser$InvalidFrameProtocolException: Invalid Frame Type, received: 84
at io.netty.handler.codec.ByteToMessageDecoder.callDecode(ByteToMessageDecoder.java:472) ~[netty-all-4.1.30.Final.jar:4.1.30.Final]
at io.netty.handler.codec.ByteToMessageDecoder.channelInputClosed(ByteToMessageDecoder.java:405) ~[netty-all-4.1.30.Final.jar:4.1.30.Final]
at io.netty.handler.codec.ByteToMessageDecoder.channelInputClosed(ByteToMessageDecoder.java:372) ~[netty-all-4.1.30.Final.jar:4.1.30.Final]
at io.netty.handler.codec.ByteToMessageDecoder.channelInactive(ByteToMessageDecoder.java:355) ~[netty-all-4.1.30.Final.jar:4.1.30.Final]
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelInactive(AbstractChannelHandlerContext.java:245) ~[netty-all-4.1.30.Final.jar:4.1.30.Final]
at io.netty.channel.AbstractChannelHandlerContext.access$300(AbstractChannelHandlerContext.java:38) ~[netty-all-4.1.30.Final.jar:4.1.30.Final]
at io.netty.channel.AbstractChannelHandlerContext$4.run(AbstractChannelHandlerContext.java:236) ~[netty-all-4.1.30.Final.jar:4.1.30.Final]
at io.netty.util.concurrent.DefaultEventExecutor.run(DefaultEventExecutor.java:66) ~[netty-all-4.1.30.Final.jar:4.1.30.Final]
at io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:897) [netty-all-4.1.30.Final.jar:4.1.30.Final]
at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30) [netty-all-4.1.30.Final.jar:4.1.30.Final]
at java.lang.Thread.run(Thread.java:834) [?:?]
Caused by: org.logstash.beats.BeatsParser$InvalidFrameProtocolException: Invalid Frame Type, received: 84
at org.logstash.beats.BeatsParser.decode(BeatsParser.java:92) ~[logstash-input-beats-6.0.0.jar:?]
at io.netty.handler.codec.ByteToMessageDecoder.decodeRemovalReentryProtection(ByteToMessageDecoder.java:502) ~[netty-all-4.1.30.Final.jar:4.1.30.Final]
at io.netty.handler.codec.ByteToMessageDecoder.callDecode(ByteToMessageDecoder.java:441) ~[netty-all-4.1.30.Final.jar:4.1.30.Final]
... 10 more
^C[WARN ] 2020-03-03 10:39:32.845 [SIGINT handler] runner - SIGINT received. Shutting down.
看到io.netty.handler.codec.DecoderException，第一感觉就是解码出错，于是把logstash的input的codec换了几个试试，都是一样的报错！
于是没头绪的我，赶紧在某度搜索一番，终于在stackoverflow看到一个类似的异常，里面看到有个回复是这样的：
意思是没有在filebeat.yml里设置logstash。当时我就不以为然：怎么可能呢。不过我还是去看了一眼我的filebeat.yml，这下可自己打脸了：
结果发现是自己还没把logstash配置中的output.logstash前面的注释符给去掉，因为这个默认是注释调的，我配置logstash的时候只管设置了hosts，忘了把上一截注释打开了。
修正之后，再重新启动filebeat，发现logstash已经可以正常接收了。
我不由得感叹，这logstash报的这个异常也太具迷惑性了，直接把我差错的路带偏了，而且偏得离谱。不过事情的发生也是由于自己太粗心！