Upgrade from Ubuntu 14.04 LTS to Ubuntu 18.04 LTS
I am looking to upgrade from Ubuntu 14.04 LTS to Ubuntu 18.04 LTS by creating a new server and migrating data. I have the new server created with the updated disk image (Ubuntu 18.04 LTS) and am currently connected with PuTTY to both servers. How do I rebuild my stack and transfer all my data (files and services) without downtime for the two servers? The "Rebuild your stack" and "Transfer your data" are quoted information from (https://www.linode.com/docs/security/upgrading/upgrade-to-ubuntu-18-04/), but the article does not go into detail on how to complete the process.
Why don't you do a dist-upgrade? You should be able to do this.
In either scenario (yours or mine) there is going to be some downtime. You can minimize it by doing it in the middle of the night, etc. In your scenario, there is also going to be a period of time while you're waiting for DNS changes to propagate. It's the nature of the beast.
I recently did this with Ubuntu 18.04 -> Debian Buster. You can give your new server a subdomain in your existing domain. When everything is done, you change your old server's domain name to point to the new server's IP address.
A side benefit is that you will discover how many places you have the hostname hard-coded into something while you're building the new server. I used a nanode as the new server while it was under construction to minimize cost. When I got done and the old server was gone, I sized the nanode up to the proper size.
The dist-upgrade continuously fails when it is completed. I believe this is due to changes in the networking features that were changed in Ubuntu 16.04. I would have loved to complete this, but it really just couldn't be done with the dist-upgrade option in my case.
Ah…OK. Understandable. What I did was spin up a nanode. I built my Server 2 on the nanode…and tested the crap out of it. When the time came, I switched the domain name to the nanode and sized it up to the original size of Server 1.
I shut down and eventually deleted the old Server 1.
Of course, in this process, I switched from Ubuntu 18.04 to Debian 10 too. I was dissatisfied by the amount of cruft in Ubuntu 18.04 designed to push ads in front of me.
Since Debian is directly upstream from Ubuntu, the conversion wasn't very hard.