Netflow configuration videos released on the ACI youtube channel this week:
Part 1 - https://www.youtube.com/watch?v=6Yl_GelaS7g
Part 2 - https://www.youtube.com/watch?v=LQCZdf9Sux0
You need to increase the size of your APIC cluster, this guide will tell you how:
http://www.cisco.com/c/en/us/td/docs/switches/datacenter/aci/apic/sw/kb/b_KB_Cluster_Management.html#task_3F7041739BD147B3A3BA9C2EA42115F8