Why does validation fail on the 'Cluster connection test' when using the MATLAB Job Scheduler?

Why does validation fail on the "Cluster connection test" when I am using the MATLAB Job Scheduler?

Validation fails with the following error message:

ERROR: Could not contact an MJS lookup service on host 'ah-hostname'. Possible reasons for this problem are:1. MJS has not been started, has crashed, or has been shut down.
2. A firewall is blocking communication between this computer and 'ah-hostname'.
3. This computer cannot resolve the hostname of 'ah-hostname', it resolves it to an incorrect IP address.
4. 'ah-hostname' resolves its own hostname to an incorrect IP address.
5. Network routers are unable to route traffic from this computer to 'ah-hostname'.

The hostname, ah-hostname, corresponds to the fully qualified hostname ah-hostname.dhcp.mathworks.com.
This computer resolves it to the IP address 111.22.33.44.

Answer 1

[MathWorks Support Team]

The 'Cluster Connection Test' stage verifies that the MATLAB client machine is able to communicate with the headnode running the MATLAB Job Scheduler. This tests hostname resolution, that the necessary ports are open and accepting traffic, that the mjs service is running on the headnode.  

If validation fails on this stage, here are some things you can troubleshoot:

1) Verify that the headnode, specified in the cluster profile, is up and running MATLAB Job Scheduler (MJS)

You will need to verify that MJS is running on the headnode and the mjs service has been started. There are a number of ways you can test this:

• Run Admincenter on the headnode and include 'localhost' or the machine's hostname in the host's field.
• Execute $MATLAB/toolbox/parallel/bin/nodestatus on the headnode.
• Run Admincenter on the client machine and enter the headnode hostname into the 'hosts' field
• Execute $MATLAB/toolbox/parallel/bin/nodestatus -remotehost headnode_hostname on the client machine. 

2) Verify that the necessary ports are open and accepting traffic on the MATLAB Parallel Server cluster

More information on the ports required for MATLAB Parallel Server can be found here: https://www.mathworks.com/matlabcentral/answers/94254-how-do-i-configure-matlab-parallel-server-using-the-matlab-job-scheduler-to-work-within-a-firewall

3) Verify that your MATLAB client is able to resolve the MJS hostname.

If 'ping' is enabled on your network, you can perform a ping test by pinging the MJS hostname from the MATLAB client.  Make sure to ping the MJS headnode by the hostname specified in the cluster profile.

Pre R2023a

it is important that the hostname specified in the cluster profile exactly matches the hostname the mjs services were started with. If the mjs services have chosen the wrong hostname then this can be overridden by altering the mjs_def file's HOSTNAME parameter and cleanly restarting the services.

4) Verify the hostname of the machine running MJS resolves to the desired IP address

Verify that the hostname of the machine that MJS is running on is resolving to the correct IP Address.  You can do this by pinging the hostname of the MJS headnode and comparing that to the IP Address from ifconfig, Unix, or ipconfig, Windows.

5) Contact Support

If you are still unable to validate your cluster please contact MathWorks support: https://www.mathworks.com/support/contact_us.html

NOTE: 

In releases older than R2015a the MJS Headnode will need to be able to resolve the MATLAB client's hostname. If it is unable to do this you can alter the hostname the MATLAB client shares with the headnode using:

​pctconfig('hostname', 'desktop24.subnet6.companydomain.com');

 NOTE: Starting in R2019a the following name changes occurred:

• MATLAB Distributed Computing Server was renamed to MATLAB Parallel Server 
• mdce_def was renamed to mjs_def
• mdce binary was renamed to mjs
• mjs scripts are in $MATLAB/R20XXx/toolbox/distcomp/bin for R2019a and earlier