UAM web server failover

[sophana]

Hi

Lot of people would like the UAM webserver failover feature in coova 
chilli or coovaAP.
I'd like to help implementing this.

Maybe the first step would be to agree on a spec?
So here's a simple proposition:

Add an optionnal alternate uam server parameter (or uamserver2)
Another would be the monitoring period.

Every 15-30 minutes (the monitoring period), an http request is 
alternatively sent to one of the uam urls with 
"?ping=1&nasId=xx&calledMac=xx&md5=xx" added to the url.
The http response should be a text response: Ok
If current uam response if not Ok:
  if last resonse from other uam server was Ok: set to other uam server 
(if not already).
  else: switch to not available service internal page.
else if current is OK and state was not available: set to current

If main uam server is ok and currently selecting the alternate, then 
switch back to the main uam server.

Note that the monitoring process must not be launched by cron because 
all hotspot may try to send a monitoring request at the same time.
About some more alternatives, there could be also more than 1 alternate 
server, and maybe it could be possible to use inexpensive ping requests 
in addition to http requests.

Now, about the implementation, I don't know if it would be better/easier 
to do this inside coova chilli, or in a monitoring script.


What do you think about all this?

Regards
Sophana