VxRail: Error "503 Service Unavailable" when accessing VMware vCenter

Administrators may be unable to access the vCenter. When logging on the UI, the following message is posted:

503 Service Unavailable Failed to connect to endpoint: [N7Vmacore4Http20NamedPipeServiceSpecE:0x00007f975808ee30] _serverNamespace = / action = Allow _pipeName =/var/run/vmware/vpxd-webserver-pipe)

There can be various causes for this error. Below are some possible scenarios:

1.Service are not started correctly and some services are not up and running:

# service-control --status
Running:
 lwsmd vmafdd vmcad vmdird
Stopped:
 applmgmt lookupsvc observability observability-vapi pschealth vlcm vmcam vmonapi vmware-analytics vmware-certificateauthority vmware-certificatemanagement vmware-cis-license vmware-content-library vmware-eam vmware-envoy vmware-hvc vmware-imagebuilder vmware-infraprofile vmware-netdumper vmware-perfcharts vmware-pod vmware-postgres-archiver vmware-rbd-watchdog vmware-rhttpproxy vmware-sca vmware-sps vmware-statsmonitor vmware-stsd vmware-topologysvc vmware-trustmanagement vmware-updatemgr vmware-vapi-endpoint vmware-vcha vmware-vdtc vmware-vmon vmware-vpostgres vmware-vpxd vmware-vpxd-svcs vmware-vsan-health vmware-vsm vsphere-ui vstats vtsdb wcp

2. Certificates are expired. To review the expiration, connect vCenter and run following command:

for store in $(/usr/lib/vmware-vmafd/bin/vecs-cli store list | grep -v TRUSTED_ROOT_CRLS); do echo "[*] Store :" $store; /usr/lib/vmware-vmafd/bin/vecs-cli entry list --store $store --text | grep -ie "Alias" -ie "Not After";done;

Here are different resolutions for scenario 1 and 2 above:

1.Confirm the status of the VMware vCenter Services. Ensure that all required services are up, running and functional.
If services are not started correctly, then restart them using the following KB:

Stopping, Starting or Restarting appliance services
 

2. Check whether the certificates are expired:

VxRail: Unable to Log In to vCenter Due to Expired Certificates
 

3. Review logs for a possible root causes:

/var/log/vmware/vsphere-client/logs/

/var/log/vmware/vpxd 

For further troubleshooting, review the official Broadcom KB:

https://knowledge.broadcom.com/external/article?legacyId=67818

On VxRail 4.7 (vSphere 6.7), there was a historical issue related to ISO with lengthy name mounted on any number of Virtual Machines:

This made it too long for the database, as per the following KB:

Cannot connect host to vCenter due to error: string too large for database (55610)