README

Kubecat

Kubecat is a utility for directly manipulating the etcd state of a Kubernetes cluster. This is a dangerous operation and should only be done by experienced operators who understand the risks. Directly modifying etcd can lead to inconsistencies in the cluster state and potential data loss.

Use this utility at your own risk. Always take a backup of your etcd cluster before making any changes.

Installation

The project can be built with make.

Usage

Kubecat can be used to extract Kubernetes objects stored in etcd to YAML, and vice versa.

Reading from etcd

To read an object from etcd, use the following command:

kubecat <etcd-key> --etcd-endpoint=<etcd-endpoint> --certfile=<path-to-cert> --keyfile=<path-to-key> --cafile=<path-to-ca> > output.yaml

Writing to etcd

To write an object to etcd, use the following command:

kubecat <etcd-key> --etcd-endpoint=<etcd-endpoint> --certfile=<path-to-cert> --keyfile=<path-to-key> --cafile=<path-to-ca> --write < input.yaml

Environment Variables

Kubecat supports the following environment variables, you can use them instead of flags to configure etcd client:

• ETCDCTL_ENDPOINTS: Comma-separated list of etcd endpoints (default: localhost:2379)
• ETCDCTL_CACERT: Path to the CA certificate file
• ETCDCTL_CERT: Path to the client certificate file
• ETCDCTL_KEY: Path to the client key file

Example: Changing a PersistentVolume's CSI driver

Let's say we want to change a PersistentVolume's CSI driver from "cephfs.csi.ceph.com" to "cephfs.kernel.csi.ceph.com", and the volumeAttributes mounter from "fuse" to "kernel".

First, we extract the PersistentVolume's manifest:

kubecat /registry/persistentvolumes/<pv-name> --certfile=<path-to-cert> --keyfile=<path-to-key> --cafile=<path-to-ca> > pv.yaml

Then, we use jq to change the spec.csi.driver and spec.csi.volumeAttributes.mounter fields in the manifest:

cat pv.yaml | jq '.spec.csi.driver="cephfs.kernel.csi.ceph.com"' | jq '.spec.csi.volumeAttributes.mounter="kernel"' > modified_pv.yaml

(Note: This requires jq installed on your system.)

Finally, we write the modified manifest back to etcd:

kubecat /registry/persistentvolumes/<pv-name> --certfile=<path-to-cert> --keyfile=<path-to-key> --cafile=<path-to-ca> --write < modified_pv.yaml

After these steps, the PersistentVolume's CSI driver and mounter will be updated in the Kubernetes etcd state.

Again, please use this utility with extreme caution. Making direct modifications to the Kubernetes etcd state can lead to data inconsistencies and potential data loss. Always take a backup of your etcd cluster before making any changes.