I have installed a Kubernetes cluster of 3 nodes with the calico network plugin. For some reason I decided to remove totally kubernetes and reisntall it with a different network plugin: Flannel.

All seemed fine until I tried to deploy my first container.

kubectl describe pod/cassandra return the following error:

Unknown desc = [failed to set up sandbox container "957f68c3cbe9b230b0e2bd6729a12c340f903de568622e28e335f7b48563a445" network for pod "cassandra-d7db46b86-dz7ck": networkPlugin cni failed to set up pod "cassandra-d7db46b86-dz7ck_default" network: error getting ClusterInformation: Get https://[10.96.0.1]:443/apis/crd.projectcalico.org/v1/clusterinformations/default: x509: certificate signed by unknown authority (possibly because of "crypto/rsa: verification error" while trying to verify candidate authority certificate "kubernetes"), failed to clean up sandbox container "957f68c3cbe9b230b0e2bd6729a12c340f903de568622e28e335f7b48563a445" network for pod "cassandra-d7db46b86-dz7ck": networkPlugin cni failed to teardown pod "cassandra-d7db46b86-dz7ck_default" network: error getting ClusterInformation: Get https://[10.96.0.1]:443/apis/crd.projectcalico.org/v1/clusterinformations/default: x509: certificate signed by unknown authority (possibly because of "crypto/rsa: verification error" while trying to verify candidate authority certificate "kubernetes")]
  Normal   SandboxChanged          3s (x3 over 18s)  kubelet, <node name>  Pod sandbox changed, it will be killed and re-created.

By reading at the errors it seems that the calico plugin is still used by Kubernetes, although I removed it and installed the Flannel plugin.

How can I clean this mess ?