Application Snapshot

Overview

Application Snapshot is a feature of ZEDEDA Cloud that enables you to save the current state (take a snapshot) of an application instance and then to rollback that instance to that state. Snapshots and rollbacks will help you recover from problems your application instance might encounter during upgrade, data migration, or normal operation. The rest of this guide will get you started with Application Snapshot.

When you take a snapshot of an application instance, ZEDEDA Cloud saves the instance’s current configuration and volume instance data. When you roll your application instance back to its snapshot, ZEDEDA Cloud will shut down your instance, restore it to the snapshot’s state, and reboot it. You can take separate snapshots for each application instance running on an edge node, giving you the flexibility to roll each instance back to a specific point in time.

Volume instance names

Volume instance names are post-fixed with a version number: “_0”, for example. The Purge and Update operation automatically increments this number when it creates new volume instances, indicating that the application instance is using the new volume instances. Normally, the Purge and Update process will delete the older versions. When you create a new snapshot, however, the Purge and Update process will leave the older versions. When you rollback to a volume instance’s snapshot, the Purge and Update process will delete the newer volume instance version and reactivate the older instance version.

Operational considerations

Before you begin using snapshots in your enterprise, there are a few important things to consider.

• Each application instance can only have a single snapshot.
• Each snapshot can only be used for a rollback a single time.
• Snapshots always apply to all volume instances associated with the application instance.
• Snapshots of entire edge nodes is not supported.
• When you create a snapshot, the Purge and Update process will delete an existing snapshot to make room for the new one.
• After you delete a snapshot, the associated files are not immediately deleted from your device's drives. These files will not be deleted until the application instance reboots.

Note that Application Snapshots are not meant to replace your existing disaster recovery strategies. ZEDEDA recommends that you continue to use the disaster recovery strategies provided by your underlying infrastructure. For example, your database provider likely has more comprehensive backups than what snapshots can provide. Instead, please use snapshots to supplement your existing strategies.

Note also that if the state of your edge node changes significantly after you take a snapshot, the snapshot may no longer be compatible with your node. For example, if certain hardware resources, such as a network interface, have been removed from the node or allocated to another entity (e.g., another application) on the same node, it may not be possible to rollback to the snapshot.

Prerequisites

User prerequisites:

• You should have Administrative privileges in your enterprise.
• You should be familiar with edge applications and edge application instances.

System prerequisites:

• Application Snapshot is available only for EVE-OS versions 10.8.0 and newer.
• You must be using ext4 volumes.

Workflows

The following procedures will familiarize you with the fundamental operations of Application Snapshot.

Be aware that at this time, Application Snapshot is available exclusively through the ZEDEDA GUI. ZCLI support is not available.

View snapshots

You can view an application instance's snapshots in its Storage page. To do so, follow these steps:

1. Click on Edge App Instances in the side-nav.
2. Select your edge app instance from those available.
3. Click on your instance’s Storage tab.
4. See the list of App Instance Volume Snapshots.

Create a snapshot

You can optionally create snapshots during the purge and update process. To do so, follow these steps:

1. Click on Edge App Instances in the side-nav.
2. Select your edge app instance from those available. 
3. Click on the meatball icon at the top-right corner of the page.
4. Select Purge & Update. A confirmation message will appear.
5. Select the Create a snapshot on purge & update checkbox.
6. Click Purge & Update.
   • This process will take a few minutes because the app instance needs to restart.

Note that changes to an application image’s configuration in the Application Marketplace will cause an “Update Available” prompt to appear in the associated application instance pages. This prompt will ask if you want to initiate a purge and update process. You can also optionally create a snapshot when you trigger a purge and update in this way.

Delete a snapshot

You can delete an application instance's snapshots in its Storage page. To do so, follow these steps:

1. Click on Edge App Instances in the side-nav.
2. Select your edge app instance from those available.
3. Click on your instance’s Storage tab.
4. Scroll down to the App Instance Volume Snapshots section.
5. Identify the snapshot you will delete.
6. Click the associated trash bin icon in the Action column.
7. Optional: if you want to delete all of the snapshot-related files from your node’s drive, restart the app instance.

Rollback to a snapshot

You can rollback an application instance from its Storage page. To do so, follow these steps:

1. Click on Edge App Instances in the side-nav.
2. Select your edge app instance from those available.
3. Click on your instance’s Storage tab.
4. Scroll down to the App Instance Volume Snapshots section.
5. Identify the snapshot you will rollback to.
6. Click the back arrow icon. A confirmation box will appear.
7. Click Rollback.

Observe the status of the rollback operation in the snapshot’s Status column. After a successful rollback, it will read “Activated” and the rollback button will become inactive.