For a while now yum's default failover method has been 'roundrobin'. That is to say when presented with either a list of baseurls or a mirror list, yum (via urlgrabber) will randomize the list of urls so that the first one used is "random" and the failover should that one fail is also "random". To the best of my knowledge this has worked well, particularly in the cases of a static list of baseurls or a static mirror list. Fedora used to employ these methods.
However, Fedora now has Mirror Manager. Mirror Manager is able to create intelligent mirror lists, both pre-randomized and even intelligently ordered. What is intelligently ordered? Lets use the site local mirror as an example. Mirror Manager allows you to define a site local mirror for a given netblock. This is so that without changing yum configuration, you can effectively drive all yum traffic to a local mirror for your site. However should your mirror not be reachable for whatever reasons, a set of fallback mirrors should be provided. Mirror Manager can provide a list that has the site local first, and then the randomized list based upon geoip information. Because the list(s) are pre-sorted, failover method of roundrobin is not necessary, and in the case of site local mirrors actively harmful. We have worked around this issue in Fedora 8 (which was the point where we introduced Mirror Manager pre-ordered lists) by overriding the failover method in the repo config files to priority (which assumes a pre-ordered list). Unfortunately, I realized yesterday that this is not helpful for yum based/using tools such as pungi, livecd-creator, anaconda, mock, revisor, etc... Each of these tools would have to grow the ability to set the failover method, either globally or on a per repo basis. This is something of a usability problem, a somewhat cryptic option to present to users, and hard to discover the correct "answer". What I'd like to propose instead is that yum's default failover setting of roundrobin be changed to priority. This would allow any yum tool using Fedora's Mirror Manager to return mirror lists work without adjusting default config. This would mean that consumers of static non-ordered lists would need to override config, however I posit that in the F8+ world this is not the most common case. Certainly not for Fedora. I'm unaware of what method CentOS uses to generate mirror lists though, however they would have a good amount of lead time before this setting would be seen in RHEL6 (RHEL to the best of my knowledge doesn't use mirror lists, it uses the rhn plugin to determine what repo urls to access so this wouldn't necessarily effect RHEL). Thoughts? -- Jesse Keating Fedora -- All my bits are free, are yours?
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