I tried to fix the mirror last night, which we are using at this point ONLY for the installer, since we switched to using conda list --explicit in
DM-24972, but fixing the URLs for the mirroring seems to have garbled up index.html in a weird way, and subsequently I had tried to remove the use of conda mirroring last night before the nightly, but I missed a line for the OS X tarballs (which is why the job failed)
As for history of the mirror, before mid 2017, packages and installer on repo.continuum.io were not served Cloudflare CDN, which is around the time we setup the mirror. Sometime after that, packages for defaults and conda-forge moved to the Cloudflare CDN. Soon after that was the rollout of repo.anaconda.com, corresponding with a renaming of continuum analytics to Anaconda, Inc.
So I think we shouldn't use (maintain really - we're not using it for the most part) the mirror anymore and we could free it up from S3. The PR to jenkins-dm-jobs reflects this.
Also, update-cmirror is the only job running in the infra weekly job. That job and associated cron job for it has been removed.