longhorn/docs/snapshot-backup.md

# Snapshot

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.

#### Note about the block level snapshot

Longhorn is a `crash-consistent` block storage solution.

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.

# Backup
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.

A corresponding snapshot is needed for creating a backup. And user can choose to backup any snapshot previous created.

A backupstore is a NFS server or S3 compatible server.

A backup target represents a backupstore in Longhorn. The backup target can be set at `Settings/General/BackupTarget`

See [here](#set-backuptarget) for details on how to setup backup target.

### Recurring snapshot and backup
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.

## Set BackupTarget

The user can setup a S3 or NFS type backupstore to store the backups of Longhorn volumes.

If the user doesn't have access to AWS S3 or want to give a try first, we've also provided a way to [setup a local S3 testing backupstore](https://github.com/yasker/longhorn/blob/work/docs/backup.md#setup-a-local-testing-backupstore) using [Minio](https://minio.io/).

### Setup AWS S3 backupstore
1. Create a new bucket in AWS S3.

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:

```
AWS_ACCESS_KEY_ID: <your_aws_access_key_id>
AWS_SECRET_ACCESS_KEY: <your_aws_secret_access_key>
```

4. Go to the Longhorn UI and set `Settings/General/BackupTarget` to
```
s3://<your-bucket-name>@<your-aws-region>/
```
Pay attention that you should have `/` at the end, otherwise you will get an error.

Also please make sure you've set **`<your-aws-region>` in the URL**.

For example, for Google Cloud Storage, you can find the region code here: https://cloud.google.com/storage/docs/locations

5.  Set `Settings/General/BackupTargetSecret` to
```
aws-secret
```
Your secret name with AWS keys from 3rd point.

### Setup a local testing backupstore
We provides two testing purpose backupstore based on NFS server and Minio S3 server for testing, in `./deploy/backupstores`.

Use following command to setup a Minio S3 server for BackupStore after `longhorn-system` was created.
```
kubectl create -f https://raw.githubusercontent.com/rancher/longhorn/master/deploy/backupstores/minio-backupstore.yaml
```

Now set `Settings/General/BackupTarget` to
```
s3://backupbucket@us-east-1/backupstore
```
And `Setttings/General/BackupTargetSecret` to
```
minio-secret
```
Click the `Backup` tab in the UI, it should report an empty list without error out.

The `minio-secret` yaml looks like this:
```
apiVersion: v1
kind: Secret
metadata:
  name: minio-secret
  namespace: longhorn-system
type: Opaque
data:
  AWS_ACCESS_KEY_ID: bG9uZ2hvcm4tdGVzdC1hY2Nlc3Mta2V5 # longhorn-test-access-key
  AWS_SECRET_ACCESS_KEY: bG9uZ2hvcm4tdGVzdC1zZWNyZXQta2V5 # longhorn-test-secret-key
  AWS_ENDPOINTS: aHR0cDovL21pbmlvLXNlcnZpY2UuZGVmYXVsdDo5MDAw # http://minio-service.default:9000
```
Notice the secret must be created in the `longhorn-system` namespace for Longhorn to access.


### NFS backupstore

For using NFS server as backupstore, NFS server must support NFSv4.

The target URL would looks like:
```
nfs://longhorn-test-nfs-svc.default:/opt/backupstore
```

You can find an example NFS backupstore for testing purpose [here](https://github.com/rancher/longhorn/blob/master/deploy/backupstores/nfs-backupstore.yaml). 


## Setup recurring snapshot/backup

Longhorn volume supports recurring jobs for automatic backup and snapshot creation.

### Set up recurring jobs for StorageClass

Users can set field `recurringJobs` in StorageClass. Any volume created using this StorageClass will have those recurring jobs automatically set up.

Field `recurringJobs` should follow JSON format. e.g. 

```
kind: StorageClass
apiVersion: storage.k8s.io/v1
metadata:
  name: longhorn
provisioner: rancher.io/longhorn
parameters:
  numberOfReplicas: "3"
  staleReplicaTimeout: "30"
  fromBackup: ""
  recurringJobs: '[{"name":"snap", "task":"snapshot", "cron":"*/1 * * * *", "retain":1},
                   {"name":"backup", "task":"backup", "cron":"*/2 * * * *", "retain":1}]'

```

Explanation:

1. `name`: Name of one job. Do not use duplicate name in one `recurringJobs`. And the length of `name` should be no more than 8 characters.

2. `task`: Type of one job. It supports `snapshot` (periodically create snapshot) or `backup` (periodically create snapshot then do backup) only.

3. `cron`: Cron expression. It tells execution time of one job.

4. `retain`: How many snapshots/backups Longhorn will retain for one job. It should be no less than 1.