Introduction
Volume instances provide the following services for edge nodes:
- storing working copies of apps that can be modified (like installed programs)
- providing space for edge apps to save data while running (like files or logs)
- allowing applications to share data with each other
When deploying an application to an edge node, it’s important to consider how it will handle persistent data. If your application requires data persistence, then you should configure a volume instance accordingly. If the application instance does not have any persistent data requirements, then the content tree will be set up automatically.
Select an Appropriate Volume Instance Type
When you are installing an edge application on an edge node, you will need to choose an appropriate type of volume instance, for example Content Tree or Block Storage.
At a high level, the process of deploying an app to an edge node is similar to the following:
- Download the immutable application image. (For example, this could be an Ubuntu ISO on a DVD that is immutable, meaning it cannot be changed or modified.)
- Create the volume on the edge node. This is the storage space on the edge node. You are basically creating space for the mutable version of the OS on your edge device. This version is capable of storing changes, files, and configs.
- Deploy the application instance. For example, a virtual disk image. This is like creating a working copy of the Ubuntu OS, which can be modified.
- Boot the mutable application instance. This is similar to starting up the modifiable version of Ubuntu.
See here for a full discussion of the storage workflow process. By following this process, you are essentially converting a read-only installation file into a working and mutable (modifiable) system. However, when you are creating the volume instance on the edge node, you must specify which type of volume instance you want to create, and this involves understanding the different types of volume instances and selecting a volume instance type based on the expected use case for your deployment.
Different Types of Volume Instances
Following are the volume instance types:
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Content Tree–Selecting this type of volume instance downloads the application image, which is also known as an immutable volume. The immutable volume is selected in block storage to be converted into a mutable volume. It then gets deployed to the application instance on the edge node.
Sample Use Case: This option works well for scenarios where you want to drop-ship an edge node with the appropriate applications pre-downloaded. This process avoids the bandwidth usage and long delays required to download large files from remote locations with poor connectivity.
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Block Storage–This type of volume instance converts the immutable application image to a mutable application image. This is like converting an ISO image to a virtual disk image. The mutable application image is then spawned to run edge apps.
To create the block storage, a content tree is necessary. The user at the target location chooses the edge node with the appropriate content tree image. If the chosen edge node does not have a content tree image, then a blank storage volume instance will be created and attached to the edge node.
Sample Use Case: This option is well-suited for scenarios where edge nodes need to host applications that require ongoing data changes, such as analytics tools.
Note: In addition to specifying the type of volume instances, you will also have the option to determine whether the volume instance should be persistent or purgeable. Persistent makes the volume instance non-purgeable, meaning that when you purge and update an app, the data in the persistent volume will be retained. However, if a volume instance is purgeable, then everything in that volume instance will be erased. This option can be set on a per-volume basis and is typically done when creating the volume instance in the app image definition in the marketplace.
List View
After you log into ZEDEDA GUI:
- Hover on Library in the side nav on the left of the page.
- Click Volume Instances.
- Click the Expand icon at the top right of your page to view the summary panel.
The ‘Summary Panel’ for volume instances displays the total number of application images under ‘Run State Distribution' and 'Type Distribution' sections. You can hover your cursor over each of the donuts to display the number of each.
The volume instances are shown in list view with columns for name, type, run state, and EVE version.
Detail View
You can drill down further to see additional details about a particular volume instance:
- Click any of the volume instances shown in list view.
- The ‘Status’ tab displays the Run State, Current Size, and Hash value.
- The ‘Basic Info’ tab shows the Identifier, Name, Title, and many other parameters. These fields are described in more detail in the section about creating a volume instance.
Next Steps
This is a series of articles. You will likely follow them in this order.
- Volume Instance Overview - You are here!
- Create a Volume Instance
- Manage a Volume Instance
- Use the ZEDEDA CLI to Manage a Volume Instance
After you’ve completed the series, you might be interested in the following articles.