OVF template deployment through vCenter fails when upload stops midway

Products

• VMware vCenter Server

Issue/Introduction

An OVF template deployment through vCenter fails before completion. The upload stops midway and the deployment does not complete successfully.

During deployment, vCenter may report that the OVF or VMDK upload failed.

You observe one or more of the following:

• OVF template deployment fails through the vSphere Client

• Upload of one or more VMDK files stops before completion

• Deployment fails after partial data transfer

• Large OVF or VMDK uploads fail intermittently

The following entries may appear in /var/log/vmware/content-library/cls.log on the vCenter Server:

ERROR | transferService-http-ae64c7029858668e5ff7190aa3129393-OVF-disk1.vmdk-upload | HttpClientEndpointImpl | Transfer session ae64c7029858668e5ff7190aa3129393: Error uploading to https://###.###.###.###/nfc/.../disk-0.vmdk: Response: 503 Service Unavailable: upstream connect error or disconnect/reset before headers. reset reason: connection termination

ERROR | transferService-http-ae64c7029858668e5ff7190aa3129393-OVF-disk2.vmdk-upload | HttpClientEndpointImpl | Transfer session ae64c7029858668e5ff7190aa3129393: Error uploading to https://###.###.###.###nfc/.../disk-1.vmdk: Response: 503 Service Unavailable: upstream connect error or disconnect/reset before headers. reset reason: connection termination

INFO  | Transfer failed! item: OVF-disk1.vmdk; bytes transferred: 3069747680; total bytes: 25918836224; error: Invalid response code: 503

INFO  | Transfer failed! item: OVF-disk2.vmdk; bytes transferred: 3079057117; total bytes: 5930519552; error: Invalid response code: 503

Environment

VMware vCenter Server

VMware ESXi

Cause

This issue occurs when the NFC upload session between vCenter Server and the target ESXi host is interrupted during transfer.

In the log example above, vCenter attempts to upload VMDK files to the ESXi NFC endpoint:

• https://###.###.###.###/nfc/.../disk-0.vmdk

• https://###.###.###.###/nfc/.../disk-1.vmdk

The target host returns:

• 503 Service Unavailable

• upstream connect error or disconnect/reset before headers

• reset reason: connection termination

This indicates that the upload session is terminated before the file transfer completes.

Common environmental causes include:

• Network interruption between vCenter Server and the target ESXi host

• Firewall session timeout during long-running uploads

• Load balancer or proxy terminating the TCP session

• L4/L7 network device resetting or closing idle or long-lived connections

• High latency or unstable network path between upload source, vCenter, and ESXi host

This behavior is commonly seen when an intermediate network device, such as a proxy or load balancer, interrupts long-running NFC transfers.

Resolution

This issue is generally environmental and not caused by a vCenter functional defect.

To resolve the issue, review the network path between the upload source, vCenter Server, and the target ESXi host.

Recommended actions:

1. Perform the upload from a system closer to the environment
   Use a jump server or virtual machine located on the same VLAN or in the same datacenter network segment as the vCenter Server and ESXi host. This reduces latency and minimizes intermediate network hops.

2. Check for firewalls, proxies, or load balancers
   Verify whether any intermediate device exists between the source system and the ESXi host. Review these devices for:

   • TCP session resets

   • idle session timeouts

   • upload/session duration limits

   • proxy termination events

3. Review timeout settings on network devices
   Large VMDK transfers can take significant time. Increase timeout values if the session timeout is shorter than the upload duration.

4. Validate network stability between vCenter and ESXi
   Confirm there are no intermittent network drops, packet loss, or connection resets during the transfer.

Additional Information

The cls.log entries show that the transfer starts successfully and progresses for both VMDK files, but fails after only part of the data is uploaded. This confirms that the deployment failure occurs during the NFC data transfer phase rather than at template validation or inventory creation.

Example from the log:

• OVF-disk1.vmdk transferred about 3.06 GB of 25.9 GB

• OVF-disk2.vmdk transferred about 3.07 GB of 5.93 GB

Because the transfer is only partially completed before receiving HTTP 503, the issue points to interruption of the network path or session handling by an intermediate device.