So, I am still using 14.04 at the moment and I know that end-of-support is coming at the end of this month unless you have extended security maintenance (which I don't).
However, I am a bit confused as to what exactly will happen. Searching online, I have seen two terms floating around: end-of-support and end-of-life. From what I can tell, both are different from what Canonical means when they refer to a release's lifespan. The trouble I have is telling if there is a difference between the two. Some pages I read treat them interchangeably while others do not. Some posts I have read use end-of-life to refer to when the repositories get moved/archived; thus preventing things such as the auto-update from working.
Regardless of which is which, when does the Ubuntu repository get archived? There doesn't seem to be a mention of that on the information page and the online posts I found simply mention that it happens, not when.
Best Answer
Ubuntu 12.04 LTS had 5 years of supported life, so 5 years will not be reached until at least 17-April-2018 (https://wiki.ubuntu.com/Releases or https://lists.ubuntu.com/archives/ubuntu-announce/2014-April/000182.html) and many pages say it's not till end-of-month or 30-April-2019.
Many pages will tell you that when a release reaches EOL, after this date archives will be moved from
archive.ubuntu.comtoold-releases.ubuntu.com, it'll be country mirrors will drop the release, and mirrors also will drop it. If you look at https://launchpad.net/ubuntu/+archivemirrors you can get a glimpse of how up-to-date mirrors are, some are listed as 'last date unknown' (too long ago for counter) which means they could be much later in dropping the archives.The best example of how fast it'll occur would be 12.04 LTS reaching EOL. It took months as I recall for it's archives to be moved, which is a huge contrast to 17.04 which took in comparison only hours. LTS releases are usually slower in moving, but without a set date you shouldn't rely on it.
It's easy to change your references to
archive.ubuntu.comtoold-releases.ubuntu.com(dropping any country code if you use it; eg. au.archive.ubuntu.com becomesold-releases.ubuntu.comtoo). If you are fully up-to-date before this move occurs though, I would expect ado-release-upgradeto be able to work anyway (I haven't tested it though), it gets far more complex if the next release (16.04 LTS) is EOL though.