Elastic Compute Service (ECS) uses automatic snapshot policies to periodically create automatic snapshots and back up data stored on system and data disks. You can use automatic snapshot policies to improve data security and fault tolerance.

Use scenarios

Automatic snapshot policies allow ECS to create snapshots on a regular basis at scheduled points in time to protect data stored on disks and improve system security and fault tolerance. When applications such as individual websites or databases deployed on an ECS instance are exposed to attacks due to system vulnerabilities, you may not be able to manually create snapshots in a timely manner. In these cases, you can use the most recent automatic snapshots to roll back the affected disks to reduce loss.

You can also specify an automatic snapshot policy to create snapshots before you perform regular system maintenance tasks. This ensures that snapshots are created and eliminates the need to manually create snapshots.

Limits

When you use automatic snapshot policies, take note of the following items:

  • For information about the quota of automatic snapshot policies per region for an Alibaba Cloud account and the maximum number of automatic snapshots that can be retained for a disk, see the "Snapshot limits" section in Limits.
  • If the maximum number of automatic snapshots has been reached, the oldest automatic snapshot is automatically deleted when a new automatic snapshot is created.
  • If you modify the retention period of automatic snapshots in an automatic snapshot policy, the modification is applied to subsequent snapshots but not to existing snapshots.
  • You can create automatic snapshots only for disks that are in the In Use state.
  • Automatic snapshot policies cannot be applied to local disks.
  • Automatic snapshot policies can create only normal snapshots. They cannot create local snapshots.
  • If a snapshot is being manually or automatically created at a scheduled point in time of an automatic snapshot policy, the automatic snapshot policy does not create an automatic snapshot at this scheduled point in time.
  • When an automatic snapshot is being created for a disk, manual snapshots cannot be created for the disk.

Common operations

The following figure shows the common operations that you can perform for automatic snapshots from the time when an automatic snapshot policy is created to the time when the automatic snapshots are released. Automatic snapshot
Operation Description References
Create an automatic snapshot policy Create an automatic snapshot policy and specify in it when to create automatic snapshots and how long to retain the snapshots.
Apply an automatic snapshot policy Apply an automatic snapshot policy to a disk to automatically create snapshots for the disk on a regular basis.
Modify an automatic snapshot policy Modify the information of an automatic snapshot policy, such as the creation time and retention period of automatic snapshots.
Create automatic snapshots on a regular basis ECS creates snapshots on a regular basis based on automatic snapshot policies. None
Release automatic snapshots Automatic snapshots can be deleted by using one of the following methods:
  • Automatic deletion:
    • When the retention period specified in the associated automatic snapshot policy for an automatic snapshot ends, the snapshot is deleted.
    • If the maximum number of automatic snapshots has been reached, the oldest automatic snapshot is deleted when a new automatic snapshot is created.
    • After Delete Automatic Snapshots While Releasing Disk is enabled for a disk, the automatic snapshots of the disk are deleted when the disk is released.
  • Manual deletion: You can manually specify and delete automatic snapshots.