hadoop slave cannot connect to master:8031 - hadoop

Question

I'm a total hadoop newbee. I set up hadoop on two machines master and slave following this tutorial (I obtained the same error following this other tutorial).
Problem: After starting dfs and yarn, the only node appearing on localhost:50070 is the master, even if the right processes are running on the master (NameNode, DataNode, SecondaryNameNode, ResourceManager) and on the slave (DataNode).
The nodemanager log of the slave reports: INFO org.apache.hadoop.ipc.Client: Retrying connect to server: master/192.168.0.14:8031. Already tried 10 times.
Note that:
I have already edited yarn-site.xml following this thread.
I have disabled the firewall on the master
I ran netstat -anp | grep 8031 on the master and confirmed that there are a couple of processes listening on port 8031 using tcp.

Answer 1

I suffered from the same problem, and these steps may help.
Make sure your namenodes can negotiate with your datanodes.
hadoop#namenode-01:~$ jps
8678 NameNode
9530 WebAppProxyServer
9115 ResourceManager
8940 SecondaryNameNode
9581 Jps
hadoop#datanode-01:~$ jps
8592 NodeManager
8715 Jps
8415 DataNode
Check your nodemanager-datanode-01.log from $HADOOP_HOME/logs reports.
INFO org.apache.hadoop.ipc.Client: Retrying connect to server: namenode-01/192.168.4.2:8031. Already tried 8 time(s);
Check if your yarn.resourcemanager.resource-tracker.address listen on ipv6 instead of ipv4.
hadoop#namenode-01:~$ netstat -natp
tcp6 0 0 127.0.2.1:8088 :::* LISTEN 9115/java
tcp6 0 0 127.0.2.1:8030 :::* LISTEN 9115/java
tcp6 0 0 127.0.2.1:8031 :::* LISTEN 9115/java
tcp6 0 0 127.0.2.1:8032 :::* LISTEN 9115/java
tcp6 0 0 127.0.2.1:8033 :::* LISTEN 9115/java
If your yarn addresses listen on ipv6, maybe you should disable ipv6 first.
sysctl -w net.ipv6.conf.all.disable_ipv6=1
sysctl -w net.ipv6.conf.default.disable_ipv6=1
Finally, the default yarn addresses are like this:
yarn.resourcemanager.resource-tracker.address ${yarn.resourcemanager.hostname}:8031
Check your /ect/hosts to avoid misconfigurations.
hadoop#namenode-01:~$ cat /etc/hosts
127.0.2.1 namenode-01 namenode-01 (for example, this line config hostname as 127.0.2.1, delete this line)
192.168.4.2 namenode-01
192.168.4.3 datanode-01
192.168.4.4 datanode-02
192.168.4.5 datanode-03