Longhorn is a distributed block storage system for Kubernetes. Longhorn is lightweight, reliable, and easy-to-use. You can deploy Longhorn on an existing Kubernetes cluster with one simple command. Once Longhorn is deployed, it adds persistent volume support to the Kubernetes cluster.
Longhorn implements distributed block storage using containers and microservices. Longhorn creates a dedicated storage controller for each block device volume and sychronously replicates the volume across multiple replicas stored on multiple nodes. The storage controller and replicas are themselves orchestrated using Kubernetes. Longhorn supports snapshots, backups, and even allows you to schedule recurring snapshots and backups!
3. 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.
Longhorn can be used in Kubernetes to provide persistent storage through either Longhorn Container Storage Interface (CSI) driver or Longhorn FlexVolume driver. Longhorn will automatically deploy one of the drivers, depending on the Kubernetes cluster configuration. User can also specify the driver in the deployment yaml file. CSI is preferred.
If the Kubernetes Cluster supports creating LoadBalancer, user can then use `EXTERNAL-IP`(`100.200.200.123` in the case above) of `longhorn-frontend` to access the Longhorn UI. Otherwise the user can use `<node_ip>:<port>` (port is `30697`in the case above) to access the UI.
Longhorn UI would connect to the Longhorn manager API, provides the overview of the system, the volume operations, and the snapshot/backup operations. It's highly recommended for the user to check out Longhorn UI.
Longhorn provides the persistent volume directly to Kubernetes through one of the Longhorn drivers. No matter which driver you're using, you can use Kubernetes StorageClass to provision your persistent volumes.
A snapshot in Longhorn represents a volume state at a given time, stored in the same location of volume data on physical disk of the host. Snapshot creation is instant in Longhorn.
User can revert to any previous taken snapshot using the UI. Since Longhorn is a distributed block storage, please make sure the Longhorn volume is umounted from the host when revert to any previous snapshot, otherwise it will confuse the node filesystem and cause filesystem corruption.
It's normal for the OS to keep content in the cache before writing into the block layer. However, it also means if the all the replicas are down, then Longhorn may not contain the immediate change before the shutdown, since the content was kept in the OS level cache and hadn't transfered to Longhorn system yet. It's similar to if your desktop was down due to a power outage, after resuming the power, you may find some weird files in the hard drive.
To force the data being written to the block layer at any given moment, the user can run `sync` command on the node manually, or umount the disk. OS would write the content from the cache to the block layer in either situation.
A backup in Longhorn represents a volume state at a given time, stored in the secondary storage (backupstore in Longhorn word) which is outside of the Longhorn system. Backup creation will involving copying the data through the network, so it will take time.
2. Follow the [guide](https://docs.aws.amazon.com/IAM/latest/UserGuide/id_users_create.html#id_users_create_console) to create a new AWS IAM user, with the following permissions set:
```
{
"Version": "2012-10-17",
"Statement": [
{
"Sid": "GrantLonghornBackupstoreAccess0",
"Effect": "Allow",
"Action": [
"s3:PutObject",
"s3:GetObject",
"s3:ListBucket",
"s3:DeleteObject"
],
"Resource": [
"arn:aws:s3:::<your-bucket-name>",
"arn:aws:s3:::<your-bucket-name>/*"
]
}
]
}
```
3. Create a Kubernetes secret with a name such as `aws-secret` in the namespace where longhorn is placed(`longhorn-system` by default). Put the following keys in the secret:
Longhorn supports recurring snapshot and backup for volumes. User only need to set when he/she wish to take the snapshot and/or backup, and how many snapshots/backups needs to be retains, then Longhorn will automatically create snapshot/backup for the user at that time, as long as the volume is attached to a node.
User can find the setting for the recurring snapshot and backup in the `Volume Detail` page.
Longhorn stores its data in the Kubernetes API server, in the format of CRD. Longhorn CRDs have finalizers; user should delete the volumes and related resource first to give the managers a chance to clean up.
Before uninstalling Longhorn, the user need to delete all the PVC and PV resources which refer to a Longhorn volume in Kubernetes. Otherwise, Kubernetes may get confused because the underlying storage is gone but the PV/PVC remains.
Note that you will lose all volume data after done this. If you intend on keeping any volume data, make backups (and test restoring a volume) before proceeding.
The cleanup script removes most components, but leaves RBAC related resources and the `longhorn-system` Namespace behind. Run this command to remove these resources.
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