# Rancher Longhorn Chart

The following document pertains to running Longhorn from the Rancher 2.0 chart.

## Source Code

Longhorn is 100% open source software. Project source code is spread across a number of repos:

1. Longhorn Engine -- Core controller/replica logic https://github.com/rancher/longhorn-engine
2. Longhorn Manager -- Longhorn orchestration, includes Flexvolume driver for Kubernetes https://github.com/rancher/longhorn-manager
3. Longhorn UI -- Dashboard https://github.com/rancher/longhorn-ui

## Prerequisites

1. Docker v1.13+
2. Kubernetes v1.8+ cluster with 1 or more nodes and Mount Propagation feature enabled. If your Kubernetes cluster was provisioned by Rancher v2.0.7+ or later, MountPropagation feature is enabled by default. [Check your Kubernetes environment now](https://github.com/rancher/longhorn#environment-check-script). If MountPropagation is disabled, the Kubernetes Flexvolume driver will be deployed instead of the default CSI driver. Base Image feature will also be disabled if MountPropagation is disabled.
3. Make sure `curl`, `findmnt`, `grep`, `awk` and `blkid` has been installed in all nodes of the Kubernetes cluster.
4. Make sure `open-iscsi` has been installed in all nodes of the Kubernetes cluster. For GKE, recommended Ubuntu as guest OS image since it contains `open-iscsi` already.

## Uninstallation

**Do not attempt to immediately delete Longhorn App from Rancher UI. Longhorn propagates device mounts which can damage the host if not unmounted properly.** Follow this procedure instead.

1. To prevent damage to the Kubernetes cluster, we recommend deleting all Kubernetes workloads using Longhorn volumes (PersistentVolume, PersistentVolumeClaim, StorageClass, Deployment, StatefulSet, DaemonSet, etc).

2. [Rancher v2.0.x users only] From the `Cluster` tab, click `Launch kubectl` and run this command:
	```
	curl -sSfL https://raw.githubusercontent.com/rancher/longhorn-manager/master/deploy/scripts/cleanup.sh | bash
	```

3. From Rancher UI, navigate to `Catalog Apps` tab and delete Longhorn app.

## Troubleshooting

### I deleted the Longhorn App from Rancher UI instead of following the uninstallation procedure

Redeploy the (same version) Longhorn App. Follow the uninstallation procedure above.

### Problems with CRDs

If your CRD instances or the CRDs themselves can't be deleted for whatever reason, run the commands below to clean up. Caution: this will wipe all Longhorn state!

```
# Delete CRD finalizers, instances and definitions
for crd in $(kubectl get crd -o jsonpath={.items[*].metadata.name} | tr ' ' '\n' | grep longhorn.rancher.io); do
  kubectl -n ${NAMESPACE} get $crd -o yaml | sed "s/\- longhorn.rancher.io//g" | kubectl apply -f -
  kubectl -n ${NAMESPACE} delete $crd --all
  kubectl delete crd/$crd
done
```

### Volume can be attached/detached from UI, but Kubernetes Pod/StatefulSet etc cannot use it

Check if volume plugin directory has been set correctly. This is automatically detected unless user explicitly set it.

By default, Kubernetes uses `/usr/libexec/kubernetes/kubelet-plugins/volume/exec/`, as stated in the [official document](https://github.com/kubernetes/community/blob/master/contributors/devel/flexvolume.md#prerequisites).

Some vendors choose to change the directory for various reasons. For example, GKE uses `/home/kubernetes/flexvolume` instead.

User can find the correct directory by running `ps aux|grep kubelet` on the host and check the `--volume-plugin-dir` parameter. If there is none, the default `/usr/libexec/kubernetes/kubelet-plugins/volume/exec/` will be used.

---
Please see [link](https://github.com/rancher/longhorn) for more information.
