为什么logstash多行筛选器不匹配日志?

我正在使用海狸将日志发送到logstash。 这些日志本质上是多行的,所以我使用多行筛选器,但不知何故筛选器无法匹配日志。 logstash的输出中没有错误。 以下是我在logstash中看到的内容:

{"@source":"udp://10.238.161.213:36655/","@tags":[],"@fields":{},"@timestamp":"2013-09-23T16:37:56.653Z","@source_host":"10.238.161.213","@source_path":"/","@message":"{\"@source\": \"file://app1.example.org/ebs/app.log\", \"@source_host\": \"app1.example.org\", \"@message\": \" This is line3\", \"@tags\": [], \"@fields\": {}, \"@timestamp\": \"2013-09-23T16:38:18.150822Z\", \"@source_path\": \"/ebs/app.log\", \"@type\": \"file\"}","@type":"app"} 

示例日志行:

 This is a log line This is line2 This is line3 

Logstash conf:

 input { udp { type => "app" port => 9996 } } filter { multiline { type => "app" pattern => "^\s" what => "previous" } } output { elasticsearch { host => "127.0.0.1" } } 

海狸正在远程应用程序主机上运行,​​并被调用为:

 /usr/bin/python /usr/bin/beaver -D -P /var/lock/beaver.pid -c /etc/beaver/conf -t udp -p /ebs/ 

和/ etc / beaver看起来像:

 [beaver] udp_host: logstash.example.org udp_port: 9996 

任何想法为什么multiinefilter不匹配日志?