Calico is installing routes in the Linux kernel. Those routes are pulled out and distributed using BIRD. BIRD can do OSPF instead if you'd like.
All Calico cares about is that routes are distributed across various systems, they don't necessarily care how you do it (configure BIRD however you'd like).
BGP is surprisingly simple and easy to set up with BIRD. Setting up a route reflector with local hosts on the same L2 all peering with each other and suddenly you can route whatever IP's you want by announcing them to your peers.
Read your own paragraph before this question. Why do I need to run another process to exchange routes and configure a mesh or a route reflector? As an admin that's just another mess of processes and communication to worry about.
Just because BGP is easy for you does not mean it's easy for most server admins and devs without heavy networking backgrounds.
Wait what? How else should we be exchanging routes? Should we shove them into a distributed key value store and then having each of the nodes pull out the routes and installing them?
> As an admin that's just another mess of processes and communication to worry about.
Yet we fully expect admins to understand and build HA redundant clusters for databases, or how to manage and update all the machines under their control, and a variety of other tasks.
There is nothing inherently different about running a BGP speaking daemon. It's all config.
I don't have a heavy networking background at all. I'm a software engineer that's currently working as a system architect, but even I can understand something as simple as a route distribution system.
All Calico cares about is that routes are distributed across various systems, they don't necessarily care how you do it (configure BIRD however you'd like).
BGP is surprisingly simple and easy to set up with BIRD. Setting up a route reflector with local hosts on the same L2 all peering with each other and suddenly you can route whatever IP's you want by announcing them to your peers.
Why do people think BGP is complicated?