Web browser times out when trying to connect to remote Hadoop NameNode web UI - hadoop

Question

No firewall is active on the remote machine:
[p512788#dev09901 ~]$ sudo systemctl status firewalld
[sudo] password for p512788:
● firewalld.service - firewalld - dynamic firewall daemon
Loaded: loaded (/usr/lib/systemd/system/firewalld.service; disabled; vendor preset: enabled)
Active: inactive (dead)
Docs: man:firewalld(1)
The port is open and the application is listening on the port as far as I can tell:
[p512788#dev09901 ~]$ lsof -i:9870
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
java 11183 p512788 265u IPv4 67057 0t0 TCP dev09901.resbank.co.za:9870 (LISTEN)
My core-site.xml configuration is:
<configuration>
<property>
<name>fs.defaultFS</name>
<value>hdfs://dev09901.resbank.co.za:8020</value>
</property>
</configuration>
My hdfs-site.xml configuration is:
<configuration>
<property>
<name>dfs.namenode.name.dir</name>
<value>file:/home/p512788/hadoop_store/hdfs/namenode</value>
</property>
<property>
<name>dfs.namenode.http-address</name>
<value>dev09901.resbank.co.za:9870</value>
</property>
</configuration>
Running jps returns:
[p512788#dev09901 ~]$ jps
12960 Jps
11425 SecondaryNameNode
12649 ResourceManager
11183 NameNode
The (partial) output of $HADOOP_HOME/logs/hadoop-p512788-namenode-dev09901.resbank.co.za.log:
2020-10-20 02:20:11,885 INFO org.apache.hadoop.hdfs.DFSUtil: Starting Web-server for hdfs at: http://dev09901.resbank.co.za:9870
2020-10-20 02:20:11,895 INFO org.eclipse.jetty.util.log: Logging initialized #766ms
2020-10-20 02:20:11,967 INFO org.apache.hadoop.security.authentication.server.AuthenticationFilter: Unable to initialize FileSignerSecretProvider, falling back to use random secrets.
2020-10-20 02:20:11,975 INFO org.apache.hadoop.http.HttpRequestLog: Http request log for http.requests.namenode is not defined
2020-10-20 02:20:11,982 INFO org.apache.hadoop.http.HttpServer2: Added global filter 'safety' (class=org.apache.hadoop.http.HttpServer2$QuotingInputFilter)
2020-10-20 02:20:11,983 INFO org.apache.hadoop.http.HttpServer2: Added filter static_user_filter (class=org.apache.hadoop.http.lib.StaticUserWebFilter$StaticUserFilter) to context hdfs
2020-10-20 02:20:11,983 INFO org.apache.hadoop.http.HttpServer2: Added filter static_user_filter (class=org.apache.hadoop.http.lib.StaticUserWebFilter$StaticUserFilter) to context logs
2020-10-20 02:20:11,984 INFO org.apache.hadoop.http.HttpServer2: Added filter static_user_filter (class=org.apache.hadoop.http.lib.StaticUserWebFilter$StaticUserFilter) to context static
2020-10-20 02:20:11,999 INFO org.apache.hadoop.http.HttpServer2: Added filter 'org.apache.hadoop.hdfs.web.AuthFilter' (class=org.apache.hadoop.hdfs.web.AuthFilter)
2020-10-20 02:20:11,999 INFO org.apache.hadoop.http.HttpServer2: addJerseyResourcePackage: packageName=org.apache.hadoop.hdfs.server.namenode.web.resources;org.apache.hadoop.hdfs.web.resources, pathSpec=/webhdfs/v1/*
2020-10-20 02:20:12,005 INFO org.apache.hadoop.http.HttpServer2: Jetty bound to port 9870
2020-10-20 02:20:12,007 INFO org.eclipse.jetty.server.Server: jetty-9.3.24.v20180605, build timestamp: 2018-06-05T19:11:56+02:00, git hash: 84205aa28f11a4f31f2a3b86d1bba2cc8ab69827
2020-10-20 02:20:12,028 INFO org.eclipse.jetty.server.handler.ContextHandler: Started o.e.j.s.ServletContextHandler#4b741d6d{/logs,file:///home/p512788/hadoop-3.2.1/logs/,AVAILABLE}
2020-10-20 02:20:12,029 INFO org.eclipse.jetty.server.handler.ContextHandler: Started o.e.j.s.ServletContextHandler#8f2ef19{/static,file:///home/p512788/hadoop-3.2.1/share/hadoop/hdfs/webapps/static/,AVAILABLE}
2020-10-20 02:20:12,074 INFO org.eclipse.jetty.server.handler.ContextHandler: Started o.e.j.w.WebAppContext#5d908d47{/,file:///home/p512788/hadoop-3.2.1/share/hadoop/hdfs/webapps/hdfs/,AVAILABLE}{/hdfs}
2020-10-20 02:20:12,078 INFO org.eclipse.jetty.server.AbstractConnector: Started ServerConnector#9816741{HTTP/1.1,[http/1.1]}{dev09901.resbank.co.za:9870}
The output of telnet and nmap from one of the DataNodes
[p512788#dev09902 ~]$ nmap -p 9870 dev09901.resbank.co.za
Starting Nmap 6.40 ( http://nmap.org ) at 2020-10-20 00:36 SAST
Nmap scan report for dev09901.resbank.co.za (10.36.16.101)
Host is up (0.00027s latency).
PORT STATE SERVICE
9870/tcp open unknown
Nmap done: 1 IP address (1 host up) scanned in 0.03 seconds
[p512788#dev09902 ~]$ telnet dev09901.resbank.co.za 9870
Trying 10.36.16.101...
Connected to dev09901.resbank.co.za.
Escape character is '^]'.
Connection closed by foreign host.
Running jps on a DataNode gives:
[p512788#dev09902 ~]$ jps
24741 NodeManager
23578 DataNode
25455 Jps

Answer 1

Just faced the same problem. You can try with:
sudo ufw allow 9870/tcp
Then verify that the port is open using:
sudo ufw status verbose

Answer 2

you can try to add a row in /etc/hosts file which content is "IP Hostname"