Avalon 821 & 841 Socket connect failed => Connection refused

[ccgllc]

Woke up this morning to discover ALL my Avalons, both 821s and 841s, offline.  S9s on the same switch to the same pool are working fine.  These Avalons are spread between 3 controllers and 6 AUCs.  All have yellow lights on them.  I've tried rebooting the Pis several times - both by power cycling and soft reboots.

The cgminer API log is showing (with trivial variations):

[Firmware Version] => Avalon Firmware - 20180305
    luci: 62d814c
    cgminer: b5b497e
    cgminer-packages: 960e108
Socket connect failed => Connection refused

These machines have been working well for quite some time.

Any ideas?

[ccgllc]

Found it, compliments of Blokforge support asking me for screenshots...

My Avalons use Static IP addressing for the controllers.  My S9s use DHCP.  Ends up the DNS server tha Avalons were pointed too was having problems.