multi-tier avro agents configuration problem

Hi folks,

I ran into a configuration problem of setting up multi-tier avro agents.
The flow is as follows, and data is generated on tier1(slave3) by using
"flume-ng avro-client --conf conf -H localhost -p 41000 -F /etc/hosts"

tier1: slave3, avro source->avro sink
tier2: slave2, avro source->logger sink

When starting tier1, it always prompts an error "cannot create RPC client".
Please give me a clue how to slove the problem, thanks! I guess the
source/sink.bind is not correct.

Here is my flume conf.
===== flume-avro.conf =====

tier1.sources = source1
tier1.channels = c1
tier1.sinks = sink1

tier2.sources = source2
tier2.channels = c2
tier2.sinks = sink2

#tier1 source
tier1.sources.source1.type = avro
tier1.sources.source1.bind = localhost
tier1.sources.source1.port = 43000
tier1.sources.source1.channels = c1
tier1.channels.c1.type = memory

#tier1 sink
tier1.sinks.sink1.type = avro
tier1.sinks.sink1.hostname = slave2
tier1.sinks.sink1.port = 43000
tier1.sinks.sink1.channel = c1

#tier2 source
tier2.sources.source2.type = avro
tier2.sources.source2.bind = slave3
tier2.sources.source2.port = 43000
tier2.sources.source2.channels= c2

#tier2 sink
tier2.sinks.sink2.type = logger
tier2.sinks.sink2.channel = c2

tier2.channels.c2.type = memory

tier1.channels.c1.capacity = 100
tier2.channels.c2.capacity = 100