Experimental Physics and
Industrial Control System

Andrea michelotti via Tech-talk <tech-talk at aps.anl.gov> · Wed, 5 Jun 2024 09:20:05 +0200

Hi all,

I'm new to EPICS, but I spent a lot of time last week trying to

understand a strange behavior with cagateway. When initialized with

EPICS_CA_ADDR_LIST=<myiocdnsname0> <myiocdnsname1> ..., it works fine as

long as <myiocdnsname0> retains its IP address at (cagateway) startup.

However, if the IP changes for any reason, you get disconnected from

that IOC permanently, regardless of any timeout settings in cagateway.

Initially, I thought this was a significant bug in cagateway, but after

discussing it with Ralph and Michael, I learned that the issue could

lies in the EPICS base channel access library. It retrieves the IP

address of the specified DNS nodes at startup and does not perform any

further DNS interactions. The only way to update the IP is to restart

the service (either cagateway or the camonitor client).

In short, it seems in CA/PVA there's an assumption that one DNS name

equals one permanent, immutable IP. This is only partially true in DNS

adressing context and does not hold in modern contexts like Kubernetes.

I've posted this as a bug in both the cagateway and epicsbase projects,

but I'm not sure if the community sees it the same way. What do you think?

Thank you in advance,
Andrea

---------------------
dr. Andrea Michelotti
Head of Control Systems Service

INFN - Laboratori Nazionali di Frascati
Accelerator Division,
Bldg.2, Room 120
Via Enrico Fermi, 40
00044 Frascati (RM)

e-mail:   andrea.michelotti at infn.it
office:   (+39) 06.9403.2272
mobile:   (+39) 06.9403.8203
fax   :   (+39) 06.9403.2256
Teams :   amichelo at infn.it

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Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System