We're Armory (YC W17) and we bring Spinnaker into complex enterprise environments. Happy to answer any ?s about it. Or you can learn more at https://www.armory.io/learn/what-is-spinnaker/ and docs at http://docs.armory.io/

I haven't used Spinnaker outside of a few tutorials and experiments, but Flagger is far simpler. It's just a "Canary" CRD you install that controls nginx-ingress (in our case). Watches prometheus, nginx and does things to a deployment.

Spinnaker invents a lot of new terms and complexities. Flagger just does one thing, and it does it pretty darn well :)