Experimental Physics and
Industrial Control System

Andrew Johnson <[email protected]> · Fri, 24 Sep 2010 10:52:30 -0500

On Friday 24 September 2010 10:34:28 Eric Norum wrote:
> I don't understand the issue.
> We run multiple soft IOCs on the same linux box all the time.   They each
> get a port assigned by the kernel.  caRepeater takes care of fanning out
> the UDP requests for PV information. "It just works".

... unless someone configures a client with EPICS_CA_AUTO_ADDR_LIST=NO and 
EPICS_CA_ADDR_LIST pointing to the IP address of that linux box.  With that 
configuration each individual CA name search UDP message gets routed by the IP 
kernel to only one of the IOCs, and depending on the particular kernel that 
might always be the same IOC (thus hiding the other IOCs from that client) or 
it might round-robin between IOCs, making connection times longer.

One solution that I don't think anyone has suggested yet would be to run a CA 
name-server on each IOC box at the official port number, and have it know 
about and forward searches to all the IOCs on that particular box, or use the 
"dbl > file" approach on each IOC so the name-server knows all the PVs 
directly.  This needs no special configuration on the part of the clients, 
they can use broadcasts or directed UDP as they wish, and there's no single 
point of failure for the control system as a whole (assuming the name servers 
get started when each machine comes up).

- Andrew
-- 
The best FOSS code is written to be read by other humans -- Harald Welte

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System