Let me start this off with this build is not viable, it does no damage, and by no damage, I mean it literally does less than 10k damage a second. However, this build should hopefully not be able to die to anything. I haven't been able to create it yet, but from a purely theoretical standpoint, you have so much effective HP that damage becomes negligible. In addition we make use of absorption charges with 11 charges, basically meaning that if elemental damage isn't one-shotting us, it is healing us instead. We also use chaos innoculation, so that we take no chaos damage. Now all we have to deal with is physical damage, by getting our phys reduction up to 90%, we can then use a taste of hate flask, a purity of fire watcher's eye, and a replica innsbury edge, we only take around 6.9% physical damage. If we continue to pair that with fortify + infused channeling on cyclone, we can then bring that down even lower. Pair this with a doppelgangers guise + an eye of innocence amulet + zealots oath, we can achieve insane levels of energy shield regen. Combine all of these together, with a few more touches such as glancing blows, immune to corrupted blood on jewel, ~~mind over matter~~(doesn't work because it only applies to life, POB already accounts for this though, and damage reduction is still as high as it seemed before), and damage recouped as mana on our watcher's eye and some of our jewels (we can still use this because of the amount of mana we spend because triggered skills still use mana), temporal chains and enfeeble, we become extremely tanky. If you want to take a look the POB will be below, but I genuinely think this is the tankiest someone can be currently.

https://pastebin.com/sKSryERe