[squid-users] squid SMP notes

[Alex Rousskov]

On 11/30/2016 11:10 PM, senor wrote:
> It is unclear to me how the more recent 'multiple instance'
> configuration compares with that of 'SMP Scaling'. 
> 
> Is there a short and sweet description of pros and cons or is the
> multiple instance simply the new way? The wiki pages vary in detail of
> implementation but don't directly state any advantage of one over the
> other. Further confusing me is my need to consider SSL Interception,
> ssl_crtd helpers and ecap. To be clear, I'm not looking for
> configuration help. Just some advice on which to pursue so I'm not
> rethinking the whole thing 6 months down the road.


SMP Squid is usually the correct way to deploy a single Squid on a
single beefy machine. "Multiple instances" is the correct way to host
multiple/different/independent Squids on a single machine. In some
cases, multiple Squid instances include SMP Squid instances! The two
features are essentially orthogonal.

Multiple Squid instances are also used (and abused) as a workaround for
various current SMP Squid limitations, which is where the confusion is
often coming from. If you think of a high-level description of what you
want to do, treating Squid as a black box "proxy", then you should be
able to classify your particular use case as a "ideally, a single Squid"
or "multiple/different/independent Squids" and go from there.

[ If you know Apache web server (httpd), then temporary consider
thinking of Squid as an Apache web server configured to proxy traffic.
Does your environment require multiple Apache servers or a single one?
Similar to Squid, Apache supports SMP scale, but that is a _secondary_
question. ]

Some of the current SMP Squid limitations are important and do require
either workarounds or development, but "multiple instance" propaganda
often comes from folks who do not understand SMP or have non-technical
phobias/biases against it. Often, those folks are far more vocal than
those who understand what is going on, so it is easy to get the wrong
impression that "multiple instances" is "more recent" or "the future".

SMP Squid is gradually getting better, with fewer exceptions that
require workarounds, including workarounds that involve multiple
instances. Multiple instances support is also getting better. Again,
each orthogonal feature targets a completely different problem area.

The above summary was true for several years, and I expect it to remain
accurate for the foreseeable future.


Sorry, I cannot provide detailed answers to your other good questions
right now.


HTH,

Alex.