Yum, Proxy Cache Safety, Storage Backend

Les Mikesell lesmikesell at gmail.com
Thu Jan 24 18:49:35 UTC 2008


Warren Togami wrote:

>> Even a postman is going to have trouble when you randomize the 
>> addresses...
>>
> 
> The real solution that you need is within MirrorManager.  Perhaps today 
> MirrorManager will not do what you need.  Let us define the 
> functionality that you do need:
> 
> "Users should be able to define their own site-local netblock and 
> associate it with a preferred public mirror.  That preferred public 
> mirror will then *always* show up as the first mirror, followed by 
> others in the region."

Anything that requires coordination among any or all of the proxy 
manager or fedora users that happen to be behind the proxy just isn't 
going to happen here and I'm having trouble imagining an organization 
where it would.  Can yum make this happen automatically, or without 
intervention, can the mirrormanager list always return the same first 
choice when requested from the same address?  If that already happens, 
then maybe things aren't as bad as I thought.

> https://fedorahosted.org/mirrormanager
> Want to help write this option into MirrorManager?  The code is open.
> 
>>> Tim "Proxies is nothing but trouble" :)
> 
> The yum developers have an erroneous assumption that only "broken" 
> proxies are at fault for yum problems.  I have described at the 
> beginning of this thread that this assumption is false.  *Any* proxy 
> server that does caching will occasionally cause the partial sync yum 
> failure, or resigned RPMS will cause a failure.

I'm missing something here.  A cache is only going to resend what it got 
the first time.  If the first user got the right thing, so will the 
second.  If the first user got something wrong, don't blame the cache 
for it.

> Fortunately, the yum developers were already thinking about using unique 
> (probably SHA1) names of repodata as of yum-3.2.9 for other reasons. 
> This should solve the common partial sync failure in Fedora 9+.

This should be needed to fix the first user's problem as much as 
subsequent ones.

>> Note that if yum acted intelligently with proxies, the whole concept 
>> of mirror management could be replaced by appropriately placed squid 
>> (or similar) proxies with no configuration/maintenance other than 
>> setting them to cache large files and restricting public ones to 
>> certain targets.  Then if yum noticed that no local proxy was being 
>> used, it could use some mirrorlist-like mechanism to find one nearby 
>> and use it explicitly, eliminating any need for a reverse-proxy setup 
>> on the proxy server side.
>>
> 
> I can't begin to respond to this because of how misguided it is.

I think anything that needs individual per-distro, per-version, 
per-location management just to act like a working cache is even more 
misguided, but maybe there some other approach that would work. Perhaps 
you could ask the squid expert if a slightly more intelligent client 
could eliminate that need and make cascaded proxies work better.

-- 
    Les Mikesell
     lesmikesell at gmail.com




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