hi Fallen
i don't have a clear answer, but i can share some thoughts out of my experience on openstack with multiple customers
- for enterprise workloads, the builtin SDN OVS (-> OVN shortly) does the job quite well, so no need to change. One point of attention is scaling as by default all external traffic is passing through the network nodes, while most external SDNs have distributed (over each compute node) network exits (nokias vrs, junipers vrouter, but als ODLs ovswitch). So very large deployements you should definitely look into this.
- for specific usecase, like e.g. telco, you might need an SDN. they typically are offering complex service in their network, requiring service chaining capabilities, LBs in the network, connecting different networks and VPLS/MPLS services. those are fully mastered by network vendors and their products. -.> prefer external SDN
- which external SDN is the best?
1/ ymmv (sorry :) ) , depends on the usecases, so try to find a match between use-cases and specific features
2/ openness; ODL wins, contrail second (opensourced, but requires high technically skilled engineers for integration), nuage last, as they are not opensources (although their VRS is built on ovswitch iinm)
3/ supportability + interaction with hardware. I have two telco customers, one with mainly juniper HW, who obiously choose contrail, the other choose ACI as they mainly work with cisco. having a mix of vendors for your SDN and legacy network, might increase difficulty on support and integration.
