Merge pull request #462 from bittrance/kind-compatibility

Kind compatibility notice

docs/COMPATIBILITY.md

@@ -23,6 +23,7 @@ Spegel has been tested on the following Kubernetes distributions for compatibili
 | :green_circle: | Minikube |
 | :yellow_circle: | EKS |
 | :yellow_circle: | K3S |
+| :yellow_circle: | Kind |
 | :yellow_circle: | Talos |
 | :red_circle: | GKE |
 | :red_circle: | DigitalOcean |
@@ -49,6 +50,30 @@ EOL
 /etc/eks/bootstrap.sh
 ```
 
+## Kind
+
+Spegel uses Kind for its end-to-end tests.
+
+Discard unpacked layers is enabled by default, meaning that layers that are not required for the container runtime will be removed after consumed.
+This needs to be disabled as otherwise all of the required layers of an image would not be present on the node.
+
+In order to be more like a "real" Kubernetes cluster, you may want to set [Containerd's metadata sharing policy](https://github.com/containerd/containerd/blob/main/docs/ops.md#bolt-metadata-plugin) to `isolated`.
+
+```yaml
+apiVersion: kind.x-k8s.io/v1alpha4
+kind: Cluster
+containerdConfigPatches:
+- |-
+  [plugins."io.containerd.grpc.v1.cri".registry]
+    config_path = "/etc/containerd/certs.d"
+  [plugins."io.containerd.grpc.v1.cri".containerd]
+    discard_unpacked_layers = false
+  [plugins."io.containerd.metadata.v1.bolt"]
+    content_sharing_policy = "isolated"
+```
+
+For a full example, see the end-to-end tests' [Kind configuration](../test/e2e/kind-config-iptables.yaml) for a full example.
+
 ## K3S
 
 K3S embeds Spegel, refer to their [documentation](https://docs.k3s.io/installation/registry-mirror?_highlight=spegel) for deployment information.