Re: logging services with shell interaction

["Casper Ti. Vector" <caspervector@gmail.com>]

On Wed, Oct 20, 2021 at 09:53:58AM +0200, Ben Franksen wrote:
> Interesting, I didn't know about recordio, will take a look.

Hello from a fellow sufferer from EPICS.  (If you see a paper on some
synchrotron-related journal in a few months that mentions "automation
of automation", it will be from me, albeit not using a pseudonym.
Another shameless plug: <https://github.com/CasperVector/ADXspress3>.)

As has been said by Laurent, in the presence of a supervision system
with reliable logging and proper rotation, what `procServ' mainly does
can be done better by something like `socat' which wraps something like
`recordio', which in turn wraps the actual service process (EPICS IOC).
The devil is in the details: most importantly, when the service is to
be stopped, the ideal situation is that the actual service process gets
killed, leading to the graceful exit of `recordio' and then `socat'.

So the two wrapping programs need to propagate the killing signal, and
then exit after waiting for the subprocess; since `procServ' defaults
to kill the subprocess using SIGKILL, `recordio' also needs to translate
the signal if this is to be emulated.  `socat' does this correctly when
the `sighup'/`sigint'/`sigquit' options are given for `exec' addresses,
but its manual page does not state about SIGTERM.  `recordio' does not
seem to propagate (let alone translate) the signal; additionally, its
output format (which is after all mainly used for debugging) feels too
low-level to me, and perhaps needs to be adjusted.

At the facility where I am from, we use CentOS 7 and unsupervised
procServ (triple shame for a systemd opponent, s6 enthusiast and
minimalist :(), because we have not yet been bitten by log rotation
problems.  It also takes quite an amount of code to implement the
dynamic management of user supervision trees for IOCs, in addition
to the adjustments needed for `recordio'.  To make the situation even
worse, we are also using procServControl; anyway, I still hope we can
get rid of procServ entirely someday.

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