flume-ng 中 selector的使用

方案一

在一个flume的agent中，启用2个source，2个channel以及2个sink。组成两条独立的flow。一条flow接收一种报文类型，互不干扰。这种方案无需重写任何flume的组件，仅需修改flume的配置文件。发送方根据报文类型的不同（这里要求发送方自己必须了解报文类型）发往不同的flume监听端口（即不同flow的netcat source）。

方案二

采用selector multiplexing的方式进行选择。对收到的报文进行分类，发往不同的channel，最终送给相应的sink。

官网对于selector multiplexing的介绍大致是：selector会根据event中某个header对应的value来将event发往不同的channel（header与value就是KV结构）。刚看到这里的时候我就有个疑惑，这个header在哪里进行设置的呢？

后来查看源码后，我猜测是source在收到报文后，封装event时，打入的header。这也就意味着如果是这样的话，需要改写项目中的netcat source。netcat source需要能够区分报文的类型，或者能够得到报文发送方提供的报文类型信息，并将报文类型设置到event的header中。完成以上功能，将flume提供的NetcatSource中原来生成event的地方修改为：

bytes.get(body);
String line = new String(body);
String[] records = line.split("\t", 2);
String header = records[0];
String strBody = records[1];
Map<String, String> headers = new HashMap<String, String>();
headers.put("LOG_FILE", header);

这个headers就是一个KV结构的map。

改写好之后，只需修改配置文件即可实现

# with the License.  You may obtain a copy of the License at
#
#  http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing,
# software distributed under the License is distributed on an
# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
# KIND, either express or implied.  See the License for the
# specific language governing permissions and limitations
# under the License.

# The configuration file needs to define the sources,
# the channels and the sinks.
# Sources, channels and sinks are defined per agent,
# in this case called ‘agent‘

agent1.sources = seqGenSrc
agent1.channels = memoryChannel1 memoryChannel2
agent1.sinks = msgRollingSink1 msgRollingSink2

# For each one of the sources, the type is defined
agent1.sources.seqGenSrc.type = com.flume.source.NetcatSource
agent1.sources.seqGenSrc.bind = 192.168.19.107
agent1.sources.seqGenSrc.port = 44444
agent1.sources.seqGenSrc.header = LOG_TYPE
agent1.sources.seqGenSrc.selector.type = multiplexing
agent1.sources.seqGenSrc.selector.header = LOG_TYPE
agent1.sources.seqGenSrc.selector.mapping.CREDIT = memoryChannel1
agent1.sources.seqGenSrc.selector.mapping.OTHER = memoryChannel2
agent1.sources.seqGenSrc.selector.default = memoryChannel2

# The channel can be defined as follows.
agent1.sources.seqGenSrc.channels = memoryChannel1 memoryChannel2

# Each sink‘s type must be defined
#agent1.sinks.msgRollingSink.type = logger
agent1.sinks.msgRollingSink1.type = com.flume.sink.RollingFileSink
agent1.sinks.msgRollingSink1.sink.directory = /home/disk1/somebody/multiplexing/credit_log
#agent1.sinks.msgRollingSink.sink.directory = /home/somebody/realtime-charge-stat/input_test
agent1.sinks.msgRollingSink1.sink.rollInterval = 60

#Specify the channel the sink should use
agent1.sinks.msgRollingSink1.channel = memoryChannel1

根据如上配置文件。客户端在发送报文到flume服务器的时候，仅需在报文正文前加上CREDIT或OTHER的报文头，与报文正文用"\t"分隔开来。这样改写的netcat
source即可将报文头打入event的header，而后selector再根据header发往不同的channel/sink。

flume-ng 中 selector multiplexing 的使用