Re: dependant services

From: Avery Payne <>
Date: Mon, 08 Jun 2015 12:21:42 -0700

On 6/8/2015 11:55 AM, Laurent Bercot wrote:
> On 08/06/2015 16:00, Avery Payne wrote:
>> This is where I've resisted using sockets. Not because they are bad
>> - they are not. I've resisted because they are difficult to make
>> 100% portable between environments. Let me explain.
> I have trouble understanding several points of your message.
> - You've resisted using sockets. What does that mean ? A daemon
> will, or will not, use a socket; as an integrator, you don't have
> much say on the matter.
I'm not specifically speaking about a socket required by a daemon. I'm
talking about using sockets for activation via UCSPI, similar to the old
inetd concept.
> - What tools are available. What does that have to do with
> daemons using sockets ? UCSPI tools will, or will not, be available,
> but daemons will do as they please. If your scripts rely on UCSPI
> tools to ease socket management, then add a package dependency -
> your scripts need UCSPI tools installed, end of story.
Until now, I have been able to resist adding additional requirements.
Each tool requirement, from outside the project, looks "lightweight and
harmless", but you know as well as I do that it isn't; each external
dependency increases complexity and reduces the chance that you can port
your code.

I've tried, really, really hard to avoid this when possible. It
probably doesn't seem like that from the outside looking in, but that's
been the intent. Sometimes my decisions will appear to be silly; this
is a learning process and as I go, silly decisions have been made, and
much has been learned. I don't claim to be an expert in any sense, just
someone who took the time to work with something.

> Dependencies
> are not a bad thing per se, they just need to be controlled and
> justified.
> "UCSPI sockets" does not make sense. You'll have Unix sockets and
> INET sockets, and maybe one or two esoteric things such as netlink.
> UCSPI is a framework that helps manipulate sockets with command-line
> utilities. Use the tools or don't use them, but I don't understand
> what your actual problem is.
The problem is that there isn't an assurance that UCSPI tools are
/available/ at the point of installation; which means writing a shell
script to handle using such tools becomes complicated, I can't just
specifically code in a tool name and expect things to just work out of
the box. Compounding that is the lack of UCSPI tools being installed as
a standard part of a software package, so things like runit may have a
"standardized set" of tools that I can count on to be there, but not
Gerrit's version of UCSPI.

I got around this problem with framework tools by abstracting away the
toolset with symlinks and fall-back behavior, so to do UCSPI properly, I
would most likely do the same again. I'm not happy about my decision
but it works across the widest range of tools and has the "least"
impact. It also makes extending support to other frameworks easier via
>> So where do
>> the sockets live? /var/run? /run? /var/sockets?
>> /insert-my-own-flavor-here?
> How about the service directory of the daemon using the socket ?
> That's what a service directory is for.
Also true. I was just pointing out that it's yet another decision that
has to be made. And as I pointed out elsewhere, things like anopa
require some custom work to wedge the definitions in, complicating the
process. Adding UCSPI support just complicates it further. Call me
whiny for not wanting to put more effort in if you like; I'll admit to
it on this specific topic.
>> * Make socket activate an admin-controlled feature that is disabled
>> by default. You want socket activation, you ask for it first. The
>> admin gets control, I get more headache, and mostly everyone can be
>> happy.
> If all this fuss is about socket activation, then you can simply
> forget it altogether.
Already did. :)
>> As a side note, I'm beginning to suspect that the desire for "true
>> parallel startup" is more of a "mirage caused by desire" rather than
>> by design.
> At least, if by "parallel startup" you mean "start things as soon as
> they can be started without risk, without needless waiting times".
The question was along the lines of "sure it's something we can do, but
does that mean we should do it to begin with?" There is value to
starting things quickly when possible, but the parallel start I'm
talking about is "we can launch 2 or more processes at once and get a
massive speed gain due to multiple cores" line of thinking. That kind
of magic makes sense when you're running a farm of 1,000 web servers; it
makes zero sense when you have a large NAS/SAN and you're forcing a
fsck-on-reboot as a default behavior because the data is too valuable to
leave to chance. Or put in shorter terms, if you have to wait for
external factors, then what's the point of multi-core parallel launching?
Received on Mon Jun 08 2015 - 19:21:42 UTC

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