Quote from Pantagruel666 >>

The only artificer sub that isn't good at tanking is the Alchemist.

 Very true

Ancestral Guardian/Echo Knight w/sentinel. 

Tanking is more than just being tough to hit or having a big ol' sack of hit points. It means protecting your teammates. Fifth Edition lacks the Guardian role and mechanics of 4e, but there are ways to still do it. I'll give you my top 6 (not 5), in alphabetical order, because I'm a heavy tipper like that and I don't want anyone to know which is my favorite.

1. Barbarian (Path of the Ancestral Guardian): Part of your rage is marking enemies so they have disadvantage attacking anyone but you. Pick up a shield and don't use Reckless Attacks.
2. Barbarian (Path of the Battlerager): Found in SCAG and dwarf-only, this is a grappler build. Like above, you can effectively lock down a single enemy. Or you can be a spikey ball of death in a crowd of lesser mooks. Unlike above, you'll always want to use Reckless Attacks from 6th-level on. It's a good switch-hitting subclass. And one of the few builds I think Grappler is worth it. The second bullet is for supporting your team, and that's what the tank does.
3. Bard (College of Valor): Bardic Inspiration can protect your allies, and you can make excellent use of Shield Master.
4. Fighter (Battle Master): So, so many maneuvers, but I'll detail just one. Goading Attack works with thrown weapons and keeps their attention on you. You can "pull" off an ally.
5. Fighter (Cavalier): You have to wait a bit, but you get half of Sentinel for free. Pick someone Small so you can ride a Medium mount around in dungeons. Mounted Combatant is useful, and the DM might let you use the Sidekick rules from Tasha's. Turn that CR 1/8 pony into a Warrior and *chef's kiss*
6. Paladin (Oath of the Ancients): This is a controller with high AC, eventual resistance to all magic damage, and can dish it out when need be.

I'm currently running an Armorer. I used a V human with warcaster since I wanted to have some control abilities and they usually require concentration. I multiclassed into fighter at least 3 levels because it gets you a fighting style (I took defense, so even without plate I have a 21 AC). Action surge is never bad, especially witha pretty full spell list. For the archetype I took EK because it gives me more cantrips and spells so I don't loose out as much on my Artificer spell progression. Between booming blade and thunder gauntlets (my DM rules that they count for booming blades component cost) you can lock down most enemies, and have the AC to be on the front lines. Having the Homunculus Servant infusion is awesome too because you can then convert your BA, something you definitely won't be using every turn, into damage. It's only a d4 but it's better than nothing most rounds

Quote from sfmaceren >>

Not sure if this thread is still alive, but I saw a tank build here.

[REDACTED]

 I'm always pleased to see a list of tank builds that correctly lists Abjurerers as top of the line tanks, but this article was written recently, so there are some notably absent builds here.  Outside of access to infinite hit points (any level 20 druid, a level 20 zealot barbarian, a level 18 abjurer), which is clearly fine - they suggest a bearbarian/moon druid, which means almost no rages per day - a life cleric 1/celestial chainlock 19 has a truly ludicrous pile of healing on tap, giving them a genuinely credible real-world hit point pool.  It's even better if you're a Jorasco halfling.  And of course, any tanking discussion that doesn't discuss Twilight or Peace clerics is dropping the ball.

Actually, I take a look, and their Abjurer build includes a 1-dip into Warlock for... no specified Pact, just Armor of Agathys?  The hell?  I mean, it's not a problem, but 10 times out of 10 I'd pick a Kundarak Dwarf over a Warforged just to avoid the Warlock dip.  Going from 3 multiclass levels to 4 is a big deal for any wizard.  I do like the idea of mixing Armorer with Abjurer, though - I'm more used to straight Abjurers that are Hobgoblins or Mountain Dwarves.

It's also being casually pitched by the author of the article. And I find it a little suspect that this is the first time they've done anything on these forums in two years.

Look at the feats: sentinel, polearm mastery, and cavalier subclass for fighter. Bugbear as a race if you can for the extra reach.  

Try this

Quote from Cporter5 >>

the obvious answer is 20 (plate armor + Shield) ... but i'm sure there are interesting abilities that can increase AC above 20 without using home brew content or magic items. 

I was thinking Dragon Sorcerer and Monk? 

Dragon Sorcerer gets an ability Dragon Resilience ... this gives you a Base AC for 13 + Dex ... could this ability be stacked with unarmored defense from the monk or barbarian ...  if this is possible it would make your theoretical AC (assuming skills are maxed) would be 23. i know you cant stack unarmored defense with unarmored defense (monk/barbarian) but Dragon Resilience is technically a different skill ... ? 

what are peoples ideas ?

 I actually recently learned a way to get your AC to about 31.

What I did was my race was warforged and my class was monk. Warforged get an extra +1 AC, and the monks 'unarmoured defence' ability allows for extra AC equal to 10 + Wisdom modifier + Dexterity modifier, but only while no armour or shield is worn. So the higher your level and the more Wisdom and Dexterity you gain, the higher your AC will go, get them both to 30 with +10 modifier and your looking at 31 AC. Of course there is another method I found. If you have the tortle race, do the same thing with the class but instead of having +1 AC, you can get +7 AC while inside the shell. the only downside is your speed and the debuffs while in the shell.

The last option I have for you is slightly leaning towards homebrew. Not sure how you feel about this but... If you turn off the prerequisites for feats in the creation menu, you can use other feats to increase your AC. A specific feat I would use is the defensive duellist feat which allows you to add your proficiency bonus to your AC as a reaction when being attacked. Though as I said before, this is technically cheating/going against what you want to do.

Hope this info was helpful, and please... anyone else who sees this and thinks I have said something wrong or they have any other general feedback, please share it, I would like to hear it.

Quote from Aldyn_The_Aboslute >>

What I did was my race was warforged and my class was monk. Warforged get an extra +1 AC, and the monks 'unarmoured defence' ability allows for extra AC equal to 10 + Wisdom modifier + Dexterity modifier, but only while no armour or shield is worn. So the higher your level and the more Wisdom and Dexterity you gain, the higher your AC will go, get them both to 30 with +10 modifier and your looking at 31 AC.

 That's not how monk unarmored defense works -- it doesn't add AC, it replaces AC.

Sorry thats what i meant, but in this case add and replace mean the same thing as it only works without armour on

Quote from Aldyn_The_Aboslute >>

Sorry thats what i meant, but in this case add and replace mean the same thing as it only works without armour on

No, it doesn't mean at all the same thing. It sets your AC to 10 + Dex Modifier + Wisdom Modifier (or 20 with Dex and Wisdom both 20), Warforged adds +1 for total 21.

Monk

Beginning at 1st level, while you are wearing no armor and not wielding a shield, your AC equals 10 + your Dexterity modifier + your Wisdom modifier.

Warforged

Your body has built-in defensive layers, which can be enhanced with armor:

• You gain a +1 bonus to Armor Class.

Beyond 1st Level

 You can’t increase an ability score above 20.

The only possible way within the rules to get an ability score beyond 20 for Wisdom and Dexterity is the the magic items Manual of Quickness of Action and Tome of Understanding but those are so exceedingly rare that for the vast majority of players they might as well not exist, so they will be ignored for this exercise.

Edit: apparently there is a variant rule to be able to raise a score to 30, but I cannot find it in the DMG and I have never seen it used in play. Most characters will need every ASI they have through level to just to get the ability scores up to 20.

As a monk using Unarmored Defense, your AC EQUALS 10 + Dex Mod + Wis Mod not adds.

With the maximum values of 20 in each ability score and being a warforged, your AC is then

10 + 5 (Dex Mod) + 5 (Wis Mod) + 1 (Integrated Protection) for a total of 21.

As a note, using official sources, here is the AC I can get to:

Warforged Artificer (Armorer) 10, Warlock (Hexblade) 10.

ASI/Feats: Magic Initiate (Cleric) for Shield of Faith, Fighting Initiate (Defense), Mobile

You may infuse 6 items, two of which must be parts of your armor (armor, boots, helmet, weapon)

Plate Mail (AC = 18) + Infusion (Enhanced Defense, +2) + Shield (+2) + Infusion Repulsion Shield (+1) + Integrated Protection (+1) + Fighting Style (Defense, +1) + Cloak of Protection (+1) + Shield of Faith (+2)

AC = 28

If you attack a creature with the gauntlets, they cannot make AoO against you. If you hit, they have disadvantage against all targets but you. If they are hexblade cursed, they miss 50% of the time or you can push them with Repulsion Shield or Rebuke of the Talisman (uses reaction for each of the 3 options). You also have Mirror Image, Shield, and Blink