Harbor replication and external OCI registry: handling manifest lists on schema2‑only targets

Short answer

Harbor does not automatically split an OCI manifest list into single‑arch manifests when the target registry accepts only Docker Image Manifest V2 Schema 2. It attempts to push the list verbatim; if the target rejects it, the replication job marks the artifact as Failed and logs the error in the jobservice logs. There is no built‑in option to convert or filter manifest lists for schema‑2‑only targets.

Detailed explanation

Harbor’s replication engine acts as a proxy: for each artifact it retrieves the manifest from the source and forwards it to the destination. The engine does not inspect or transform the manifest content. When the destination registry enforces Schema 2 only, it will reject an OCI index (manifest list) with a 400 Bad Request or 415 Unsupported Media Type response. Harbor captures this response, records the failure in the replication job, and shows the status in the UI under Replication → Job History.

What the logs look like

2026-10-10 14:08:26.358Z INFO  jobservice   Pulling manifest list for "myorg/myimage:latest"
2026-10-10 14:08:26.360Z ERROR jobservice   Push failed: HTTP 415 Unsupported Media Type – target rejects OCI index

These entries appear in /var/log/harbor/jobservice.log on the Harbor host. You can tail the log while a replication job is running:

sudo tail -f /var/log/harbor/jobservice.log

Verifying the outcome

1. Check the replication UI. In Harbor, navigate to the project, click Replication, and open the job that processed the multi‑arch image. A Failed status indicates that the manifest list was rejected.
2. Inspect the target registry. Use Docker CLI to query the target:

   docker manifest inspect myregistry.io/myorg/myimage:latest
   

   If the target returned 400 or 415, no image will be present.
3. Review jobservice logs. Search for the image name:

   sudo grep -i "myorg/myimage:latest" /var/log/harbor/jobservice.log
   

   The log should contain the HTTP error code.

Configuration options

Harbor offers no flag to automatically convert an OCI index to a set of single‑arch manifests. The only configurable aspects are the replication policy (which artifacts to replicate) and the target registry URL. If you need to replicate multi‑arch images to a schema‑2‑only registry, you must either:

• Push each architecture separately from the source registry, or
• Use a registry that accepts OCI manifests (e.g., Harbor itself, Docker Registry 2.7+, or a compatible OCI registry).

What to do next

If you suspect Harbor is silently skipping the manifest list, check the replication job status and the jobservice logs. If the status is Failed and you see an HTTP 415 in the logs, the behavior is as documented. If the status is Success but the target only shows a single architecture, that would indicate that the target registry silently stripped the list, which is outside Harbor’s control.

Diagnostic detail needed

To fine‑tune the recommendation, could you provide the exact HTTP status code returned by the target registry when Harbor attempted to push the manifest list? That will confirm whether the target is rejecting the list or accepting it partially.