"503 Service Unavailable" error on the vSphere Web Client when logging in or accessing the vCenter Server
search cancel

"503 Service Unavailable" error on the vSphere Web Client when logging in or accessing the vCenter Server


Article ID: 337535


Updated On:


VMware vCenter Server


This article provides insights and troubleshooting steps when you encountered this error while logging in and accessing the vCenter Server using your vSphere Web Client.

  • Logging in to the vCenter Server or vCenter Server appliance (VCSA) using the vSphere Web Client fails.
  • Accessing the vCenter Server or vCenter Server appliance using the vSphere Web Client fails.
  • You see these errors similar to:
    503 Service Unavailable.
    503 Service Unavailable (Failed to connect to endpoint: [N7Vmacore4Http20NamedPipeServiceSpecE:0x00007fb7d00200a0] _serverNamespace = / action = Allow _pipeName =/var/run/vmware/vpxd-webserver-pipe)


VMware vCenter Server 6.0.x
VMware vCenter Server Appliance 6.7.x
VMware vCenter Server 6.5.x
VMware vCenter Server 6.7.x
VMware vCenter Server 7.0.x
VMware vCenter Server Appliance 5.5.x
VMware vCenter Server Appliance 6.5.x
VMware vCenter Server Appliance 6.0.x


This issue may occur due to a number of reasons such as:
  • The vCenter Server currently down because of maintenance.
  • The reverse Proxy service on vCenter Server is down.
  • The vSphere web client service is down.
  • Mis-configured Firewall settings.

    This mis-configuration can only occur on a Windows installation of vCenter Server.
    A VCSA installation can only have this problem if deliberate changes were made to firewall settings.


Before troubleshooting, it is critical to understand what a "503 Service Unavailable" error is.
For more insights, see

Disclaimer: VMware is not responsible for the reliability of any data, opinions, advice, or statements made on third-party websites. The inclusion of such links does not imply that VMware endorses, recommends, or accepts any responsibility for the content of such sites.

A 503 Service Unavailable error is an HTTP response status code that indicates that the server is temporarily unable to handle your request. This can be due to a number of reasons already mentioned in the cause section.

There are also different looking 503 pages on other websites:

For example:
  • 503 Service Unavailable (Failed to connect to endpoint: [N7Vmacore4Http20NamedPipeServiceSpecE:0x00007fb7d00200a0] _serverNamespace = / action = Allow _pipeName =/var/run/vmware/vpxd-webserver-pipe)
  • 503 Error
  • Service Unavailable – DNS Failure
  • HTTP Error 503
  • HTTP 503
  • 503 Service Temporarily Available
An important thing to remember is that a 503 error is a server-side error. This means that the problem exists within the vCenter Server or website (server) you are trying to access, and not your computer (client).

Troubleshooting HTTP response status code "503" on the vSphere Web Client when connecting to the vCenter Server. 

  1. Try again in a few minutes.

    Note: it is most likely that the vCenter Server is just busy acknowledging your request. The vCenter server was able to process your request and was able to respond back with the "503 Service Unavailable" error. It is just not able to acknowledge your request either because it is busy with other tasks at the moment or it currently down with very limited services due to maintenance.
  2. Try again in a few minutes on a different client. Confirm if you are still get the same error.
  3. Confirm the status of the VMware vCenter Services. Ensure all required services are up, running and functional for both the vCenter Server device and any external Platform Services Controller (PSC) device also. For more insights, see:
  1. Check if there are disk space issues on the vCenter Server or the vCenter Server Appliance. 


    Disk space issues can cause more than one service to shutdown which can result in the HTTP 503 Error Response Code.
    Disk space issues do not directly cause a 503 Error Response Code, but the services being down due to a failure causes the error.
  1. Check whether certificates are expired.
  1. Other causes of critical services being down can include:
    • Database server disconnected for Windows vCenter Server, due to:
      • database service account password change
      • network change
    • Database corruption
    • Machine account password problems per "invalid credentials LDAP Error Code 49" error when starting Inventory Services in vCenter Server 6.x
    • Very high storage communication latency
    • Very high virtual CPU contention
    • Time synchronization problems
      • between vCenter and PSC
      • between vCenter and database server
      • between vCenter and ESXi hosts
      • between vCenter and domain controllers
From the vCenter Server, investigate the vsphere_client_virgo.log file located at:
Windows vCenter Server - C:\ProgamData\VMware\vCenterServer\logs\vsphere-client\logs\
vCenter Server Appliance - /var/log/vmware/vsphere-client/logs/

Also, look at the vpxd.log file located at:
Windows vCenter Server: C:\ProgramData\VMware\vCenterServer\logs\vmware-vpx
vCenter Server Appliance: /var/log/vmware/vpxd
For more insights on Troubleshooting VMware vCenter Server, the vSphere Web Client, Storage and Networking, see the VMware vSphere Troubleshooting Guide.


For Troubleshooting Work Flow, see:

Flow chart for troubleshooting 503 service unavailable error

Additional Information

VMware strongly recommends on following Performance Best Practices on VMware vSphere 6.x/7.x

Managing the vCenter Server or vCenter Server appliance fails.