Hello @Samala, Kiran
The 503 Service Unavailable is coming from the HPC monitoring REST service, so this looks more like a head-node monitoring/service issue than an HPC Cluster Manager client problem.
On the head node, first check that the HPC services are running, particularly HpcMonitoringServer, and review the HPC-related Windows Event Logs for errors occurring when Cluster Manager starts.
You can quickly check the services with:
Get-Service *Hpc* | Select Name, Status, StartType
Restarting the failed HPC monitoring service may restore Cluster Manager temporarily, but if the 503 returns, check the monitoring service/database connectivity and certificates rather than repeatedly restarting the client.
Also confirm your HPC Pack 2019 version. Microsoft currently provides HPC Pack 2019 Update 3, with subsequent fixes, so if you're running the original 2019 release or an older update, bringing the cluster to a supported/current build should be considered.
If you can share the output of Get-Service Hpc and your HPC Pack build number, we can narrow down which service is generating the 503.
Reference: Microsoft – HPC Pack 2019 Update 3 https://www.microsoft.com/en-us/download/details.aspx?id=108564
Please "Accept the Answer" if this information helped you. This will help us and others in the community as well.