A stack is a collection of desktops. Currently Windows VDIs are stackable and in the near future we will add this feature for linux VDI environments as well.
Why make a stack?
A stack can be very useful for when you want to keep a fixed number of VDI's on hand. Say, for example, that you have 10 employees who need VDI's, with stacks they can simply reserve one VDI each and have immediate access since they are pre-built. Without a stack they would need to build the VDI's (a process that takes roughly 10 minutes) before they can have access.
The other reason to have a stack is because it makes it easier to destroy the VDI once you are done using it. Destruction can be performed manually by the user that reserved the stack (or an admin) or be handled automatically on a daily or weekly schedule. The schedule is set at the creation time of the stack. This prevents vdis from becoming stale, making them vulnerable to attack.
A stack will maintain it's size. A stack of 3 machines will always try to have 3 machines on it. If all three machines are reserved then the stack will not add more machines, you may want to consider making the stack larger if you notice all machines are often reserved on the stack. If the users destroy their VDIs on the stack a new VDIs will be provisioned until the stack has reached the desired size.
Upcoming feature: The size of the stack will be editable after creation.
TTL (Time To Live) is an advanced feature that can be used to restrict how long a user who reserves a VDI from a stack has access to it. As an example: If TTL is set to 3, then a user who reserves a vdi from the stack will only be allowed to use the vdi for 3 hours, the machine will then be destroyed and a new one will begin building.
We currently only support Windows VDI's. Linux will be coming shortly. We can do custom images with a bit of manual tinkering for organizations that require it. Get in touch.
One of the main reasons to use a stack is if you want to have users that, by design, only have access to VDI's. We call these users VDI-Users and you can read more about them here. VDI-Users receive their VDI's by being on an enclave that has only one stack and having access to nothing else on the console. The stack is the thing that feeds them their reserved VDI's.