In Juniper Apstra 5.1, a template is a design abstraction used to create a blueprint. It captures the intended topology shape and design rules without tying the design to a specific vendor's CLI. Apstra supports multiple template types to match common data center fabric architectures.

A rack-based template is used for the standard three-stage Clos (leaf--spine) approach. In this model, you define the spine logical devices and one or more rack types (containing leaf devices and optional endpoint constructs). This is the dominant pattern for EVPN-VXLAN IP fabrics: leaf switches provide server attachment, VXLAN encapsulation (VTEP function), and optional IRB gateways, while spines provide high-capacity L3 transit with ECMP.

A collapsed template is used for a spine-less (spineless) topology. Instead of a separate spine tier, a collapsed design models a fabric where leaf nodes interconnect in a mesh-like arrangement (as supported by the template type) to provide underlay reachability and redundancy. This can be useful for smaller environments or edge data centers where a full spine tier is unnecessary.

''Compressed'' and ''device-based'' are not Apstra template types. Junos v24.4 is relevant when the blueprint is instantiated and deployed, but the template type selection is an Apstra design-time decision that determines the fabric topology class.