什么是Flink。

Apache Flink® - Stateful Computations over Data Streams

Flink安装参考(官方文档)[https://ci.apache.org/projects/flink/flink-docs-release-1.7/tutorials/local_setup.html]。

这里使用单机模式。

问题表现

启动Flink

[root@VM_80_180_centos /usr/local/flink-1.7.2]# ./bin/start-cluster.sh 
Starting cluster.
Starting standalonesession daemon on host VM_80_180_centos.
Starting taskexecutor daemon on host VM_80_180_centos.

查看进程

[root@VM_80_180_centos /usr/local/flink-1.7.2]# jps
10442 StandaloneSessionClusterEntrypoint
11067 Jps
10909 TaskManagerRunner
[root@VM_80_180_centos /usr/local/flink-1.7.2]#

查看日志，发现"Could not resolve ResourceManager address"的错误。

[root@VM_80_180_centos /usr/local/flink-1.7.2]# tail -f log/flink-root-taskexecutor-*.log

2019-03-27 19:43:23,804 INFO  org.apache.flink.runtime.taskexecutor.TaskExecutor            - Could not resolve ResourceManager address akka.tcp://flink@localhost:6123/user/resourcemanager, retrying in 10000 ms: Ask timed out on [ActorSelection[Anchor(akka.tcp://flink@localhost:6123/), Path(/user/resourcemanager)]] after [10000 ms]. Sender[null] sent message of type "akka.actor.Identify"..
2019-03-27 19:43:43,843 INFO  org.apache.flink.runtime.taskexecutor.TaskExecutor            - Could not resolve ResourceManager address akka.tcp://flink@localhost:6123/user/resourcemanager, retrying in 10000 ms: Ask timed out on [ActorSelection[Anchor(akka.tcp://flink@localhost:6123/), Path(/user/resourcemanager)]] after [10000 ms]. Sender[null] sent message of type "akka.actor.Identify"..

访问Flink的web页面，发现task数全为0.

flink no task

问题原因：

taskmanager.host

Flink的taskmanager.host默认为空，会使用hostname。

[root@VM_80_180_centos /usr/local/flink-1.7.2]# ping VM_80_180_centos
PING VM_80_180_centos (100.125.80.180) 56(84) bytes of data.
64 bytes from VM_80_180_centos (100.125.80.180): icmp_seq=1 ttl=64 time=0.022 ms
64 bytes from VM_80_180_centos (100.125.80.180): icmp_seq=2 ttl=64 time=0.038 ms
64 bytes from VM_80_180_centos (100.125.80.180): icmp_seq=3 ttl=64 time=0.038 ms

Flink的jobmanager.host默认为localhost。

这里jobmanager和taskmanager绑定的ip不一样，导致出错。

解决办法：

vim conf/flink-conf.yaml

添加下面这行配置
taskmanager.host: localhost

保存退出，然后重新启动Flink，这个时候在web端就可以看到有可用task了。

flink web