Upcoming changes to downloading AltArch .iso images

Monday , 8, October 2018 Leave a comment

Greetings from the mirror-management department! This notice is for those who employ some sort of an automation to download AltArch (ie. aarch64, armhfp, i386, power9, ppc64, ppc64le) CentOS 7 .iso/.raw.xz images from mirror.centos.org. Those using a regular browser to download these images are not particularly affected, and you can continue to the next post on this blog.

Previously, only main architecture .iso image downloads from mirror.centos.org were redirected to isoredirect.centos.org, which then displayed the user a list of nearby external mirrors. We will shortly extend this configuration to cover AltArch image downloads as well, ie. direct AltArch image downloads from mirror.centos.org will no longer be possible. mirror.centos.org will still serve .rpm downloads for all architectures as before.

There are three reasons for the change. First, to save bandwidth from mirror.centos.org nodes directly managed by the CentOS Project. Most of these mirror.centos.org hosts are also used for seeding the 600+ external mirrors we have. By directing some of that .iso download traffic to external mirrors we can offer faster sync speeds for those external mirrors, and for people downloading individual rpms from mirror.centos.org. Second, most of those external mirrors offer faster download speeds to end users than what could be achieved by downloading from mirror.centos.org, so the users will benefit from this change as well. Finally, because there are much more external mirrors than mirror.centos.org  nodes, it is likely that your bits will need to travel a shorter path, conserving bandwidth globally.

The above change will be implemented some time between the releases of RHEL 7.6 and CentOS 7.6.18xx, so that external mirrors syncing CentOS 7.6.18xx content would not need to fight for bandwidth between AltArch .iso downloaders.

The other change, which has already been implemented, is related to how isoredirect.centos.org behaves when accessed with curl or wget. If you now do a wget http://isoredirect.centos.org/altarch/7/isos/i386/CentOS-7-i386-Everything-1804.iso, isoredirect will notice that you are trying to download the file and will redirect the request to the nearest external mirror. If you access the same URL with a regular browser, you will see a list of nearby mirrors from which you can pick your favourite mirror. wget will follow redirects by default, but curl needs a --location switch to follow redirects. If a filename is not specified, you will get a list of mirrors regardless of the browser used.

So, combining the effects of the above two changes: If you currently use some sort of a script that downloads AltArch .iso images from mirror.centos.org, those requests will soon be served by external mirrors instead of mirror.centos.org. In the case of wget you will only see one additional request and you probably don't need to change anything. If you use curl, you must add the --location switch to curl to follow the redirect issued by isoredirect.centos.org. If you want to eliminate one redirect, you can change mirror.centos.org to isoredirect.centos.org in your script. The rest of the URL is the same, ie. /altarch/<release>/isos/<arch>/<filename.iso or .raw.xz>

As an aside, even though mirror.centos.org nodes are managed by the CentOS Project, those servers and their hosting are donations from various organizations. If you think your organization could donate an additional server to share the load and to give us better geographical coverage, please see https://wiki.centos.org/Donate

If you have questions or concerns regarding this change, please let me know. Thanks!

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