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Old 08-01-2019, 06:55 AM   #1
miccze
LQ Newbie
 
Registered: Sep 2018
Distribution: Centos
Posts: 17

Rep: Reputation: Disabled
firewalld doesn't open port


Hello all,

I have problem with opening port in firewalld on Centos 7.
Situation:
I have server Alfa on which i run tomcat and i configured jmx port to get data about java on port 9999.
Now, on server Beta, i set up docker container with jmx-scraper image to scrape the data about tomcat on server Alfa ( configured to read data from port 9999 on server Alfa). Problem is that the scraper cannot access the port 9999 when firewall is started on server Alfa. When i stop firewall, then scpraping is happening fine.
Firewall details:
Code:
firewall-cmd --zone=public --list-ports --permanent
10051/tcp 10050/tcp 80/tcp 443/tcp 8080/tcp 9100/tcp 9999/udp 9999/tcp
Code:
firewall-cmd --get-active-zones
public
  interfaces: eth0
Code:
firewall-cmd --zone=public --list-all --permanent
public
  target: default
  icmp-block-inversion: no
  interfaces:
  sources:
  services: dhcpv6-client ssh
  ports: 10051/tcp 10050/tcp 80/tcp 443/tcp 8080/tcp 9100/tcp 9999/udp 9999/tcp
  protocols:
  masquerade: no
  forward-ports:
  source-ports:
  icmp-blocks:
  rich rules:
Code:
netstat -plaunt | grep 9999
tcp        0      0 0.0.0.0:9999            0.0.0.0:*               LISTEN      23434/java

I tried to interfere with direct mode, but it also doesnt seem to help. Iptables service is disabled.
Logs from container:
Code:
SEVERE: JMX scrape failed: java.rmi.ConnectIOException: Exception creating connection to: <server Alfa>; nested exception is:
        java.net.NoRouteToHostException: No route to host (Host unreachable)

When i stop firewall on server alfa, it immediately starts to work..
 
Old 08-01-2019, 08:41 AM   #2
berndbausch
Senior Member
 
Registered: Nov 2013
Location: Tokyo
Distribution: Redhat/Centos, Ubuntu, Raspbian, Fedora, Alpine, Cirros, OpenSuse/SLES
Posts: 3,270

Rep: Reputation: 851Reputation: 851Reputation: 851Reputation: 851Reputation: 851Reputation: 851Reputation: 851
Are you sure that Beta uses 9999? Have you tried connect to Alpha with other clients, such as telnet or netcat?
 
Old 08-01-2019, 10:22 AM   #3
miccze
LQ Newbie
 
Registered: Sep 2018
Distribution: Centos
Posts: 17

Original Poster
Rep: Reputation: Disabled
Once firewall is stopped, the scraper gets data from tomcat, which enables them on port 9999.

Also netstat from scraper:
Code:
bash-4.4# netstat -plaunt | grep 9999
tcp        0      0 ::ffff:172.17.0.3:35600 ::ffff:<alfa'sIP>:9999 TIME_WAIT   -
(means he tries making connection to alfa:9999)

nc from scraper:
Code:
nc -vz alfa 9999
alfa (alfa'sIP:9999) open
Configuration of the scraper:
Code:
cat /opt/jmx_exporter/config.yml
startDelaySeconds: 0
hostPort: alfa:9999
username:
password:
ssl: false
lowercaseOutputName: false
lowercaseOutputLabelNames: false
rules:
- pattern: '.*'

So theoretically, port is open, scraper tries to scrape from port 9999, but the connection TIME_WAITS. Once firewall is stopped, the scraper works and tomcat is exporting the data over JMX port which is 9999, so scraper tries to scrape from alfa:9999.
What does that mean? What is wrong?
 
Old 08-02-2019, 03:26 AM   #4
miccze
LQ Newbie
 
Registered: Sep 2018
Distribution: Centos
Posts: 17

Original Poster
Rep: Reputation: Disabled
The issue is resolved. It turns out that the scraper is using also rmi port for scraping. So it needed 2 ports open. As i didn't know that, tomcat didn't have specified rmi port, so it was using random port for that. And this random port was blocked by firewall obviously.
Some info about it:
http://www.perftactique.com/2018/03/...-the-firewall/

You can configure rmi port the same as the jmx port in tomcat's configuration:
-Dcom.sun.management.jmxremote.port=9999 -Dcom.sun.management.jmxremote.rmi.port=9999

Once the rmi port was specified, and port 9999 was opened in firewall, it worked.

Anyway, thanks for you contribution berndbausch

Cheers.
 
  


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