core: allow oci_layers_on_top with single manifest

[tarilabs]

when downloading single-arch (non-multi-arch) base image into oci-layout, using for example:

• skopeo copy ----multi-arch system ...
• oras copy --platform linux/arm64 --to-oci-layout ...

the base image oci-layout will not reference Index(es) but only OCI Image Manifest, the single image Manifest of the single-arch.

This modification resolves an old TODO in the code.

[tarilabs]

Tested also locally with:

kind create cluster
./e2e/deploy_distribution_registry.sh
kubectl apply -f https://github.com/cert-manager/cert-manager/releases/download/v1.16.1/cert-manager.yaml
e2e/repeat.sh kubectl apply --server-side -f https://github.com/kserve/kserve/releases/download/v0.14.0/kserve.yaml
e2e/repeat.sh kubectl apply --server-side -f https://github.com/kserve/kserve/releases/download/v0.14.0/kserve-cluster-resources.yaml
kubectl patch configmap/inferenceservice-config -n kserve --type=strategic -p '{"data": {"deploy": "{\"defaultDeploymentMode\": \"RawDeployment\"}"}}'
e2e/enable-modelcar.sh
IMAGE_DIR=download
OCI_REGISTRY_SOURCE=quay.io/mmortari/hello-world-wait:latest
OCI_REGISTRY_DESTINATION=localhost:5001/nstestorg/modelcar
# the following is done manually, but python shortcut are available
oras copy --platform linux/arm64 --to-oci-layout ${OCI_REGISTRY_SOURCE} ${IMAGE_DIR}:latest
chmod +w download/blobs/sha256/70378ac6bb0f7e7e39ce50fff837162f5fd38c4e8daf8de1a120df9a7d79d633
chmod +w download/blobs/sha256/c23ed8b7e30f5edd2417e1dd99fedad4445f3e835edb58760b2f83f2c0517878
# ...resume scenario
poetry run olot $IMAGE_DIR --modelcard tests/data/sample-model/README.md tests/data/sample-model/model.joblib
skopeo copy --tls-verify=false --multi-arch all oci:${IMAGE_DIR}:latest docker://${OCI_REGISTRY_DESTINATION}
skopeo copy --src-tls-verify=false docker://localhost:5001/nstestorg/modelcar docker-daemon:localhost:5001/nstestorg/modelcar:v1
e2e/repeat.sh kubectl apply -f e2e/isvc-modelcar.yaml
kubectl wait --for=condition=Ready isvc/my-inference-service --timeout=240s
echo "Starting port-forward..."
kubectl port-forward svc/my-inference-service-predictor 8080:80 &
PID=$!
sleep 2
echo "I have launched port-forward in background with: $PID."
echo "Check that OIP return the expected name"
curl -s http://localhost:8080/v2/models | jq -e '.models | index("my-inference-service") != null'
echo "Check that OIP produces an Inference Prediction"
curl -s -H "Content-Type: application/json" -d @e2e/data/input0.json http://localhost:8080/v2/models/my-inference-service/infer | jq
curl -s -H "Content-Type: application/json" -d @e2e/data/input1.json http://localhost:8080/v2/models/my-inference-service/infer | jq
curl -s -H "Content-Type: application/json" -d @e2e/data/input4.json http://localhost:8080/v2/models/my-inference-service/infer | jq

[Crazyglue]

looks good!

[Crazyglue]

Great cleanup!

[tarilabs]

thanks @Crazyglue @syntaxsdev