Re: CA wishlist :)

[Ralph Lange <Ralph.Lange@bessy.de>]

Hello Heinrich,

trying to comment on at least some of your questions....

> Wouldn't it be nice to specify the EPICS_CA_* values firstly through 
> functions in the library rather than environment variables only.
> And then secondly on a per-connection basis.
> So you can have seperate setup for every PV connection. ?

(Note that there is one connection between a CA client (your 
application) and the CA server (IOC), which is shared for all PVs on 
that server, so "for every PV" is different from "for every connection".)

This is not easy to implement. I've been missing this a couple of times 
for the CA Gateway, though. Would be nice.

Name resolution is done by UDP broadcasts or directed UDP messages, and 
it is highly optimized: many PV names are broadcast in one UDP message. 
In case of EPICS_CA_ADDR_LIST being set, the UDP messages are sent only 
to the specified IP addresses, but still many names in one message. As 
UDP is not reliable, a burst of UDP messages is sent for a single name 
resolution broadcast.
If you allow to specify a different EPICS_CA_ADDR_LIST for every PV, you 
would either have identify different CA domains (each with a different 
setting) and put any new PV connection into the matching domain (create 
a new one for a new config) or send the usual burst of UDPs for every 
single PV that is needed. The first option is tricky, the second would 
easily overload the network and the IOCs.
Jeff definitely has a better inside view on this issue.

> Is it possible to link casw into a program somehow? So that your 
> client program can monitor the status of a specific IOC?

The casw source is part of base - feel free to link it into one of your 
programs .... :-)

I would say there are better ways to monitor IOC health than beacon 
regularity. Beacons are sent with relatively low priority - you may have 
situations where you see a beacon anomaly while the IOC is busy, but 
still doing fine. Also bad configuration on an additional IOC may look 
like a beacon anomaly on yours.

If you install vxStats (or the Linux version done by the SLS for soft 
IOCs), you can monitor things like CPU load, FD and memory usage. Or 
load a calc record that just counts up and monitor it. All this gives 
you more and faster health info than casw.

Also have a look at the Nagios plugin that Mauro Giacchini wrote - maybe 
that is a good point to start from. You can monitor a bunch of records 
(see above), ping the IOC, and use all the nifty Nagios stuff like 
configuring what emails to send in case of alarm, schedule downtimes 
etc. pp. That fits very nicely into the Nagios approach to constantly 
monitor all your infrastructure and services within one tool.

It could also be an idea to have a casw based device support that 
reports beacon anomalies. Fixed configuration specifies the IOC to look 
for, record is counting up whenever it sees one. Additional calc records 
can be used to get the anomaly rate and raise alarms.

> And lastly - with the CA library.
> How do I control users - password ect in case of Access Control on IOC's ?

You don't.
There are no passwords in Access Control.
User and Host information is taken from the UID and hostname the client 
runs on.
There's a detailed discussion of Access Control in the Application 
Developer's Guide. ;-)

Cheers,
Ralph