This is actually an amusing encounter, as the trash before Ignis is actually arguably harder than he is. If you don't know how to handle the trash you will wipe. If you do know how you will fair just fine. Thankfully I'm here to help with that.
Pull 1: 2 Giants - These need to be tanked so that the tank is in LoS of the healer, but the Giant isn't (eg. Chromaggus / Firemaw / Flamegor style). This will prevent your healer from getting silenced - the tanks dying - and the raid wiping. The giants will also put a stacking fire damage debuff on the raid, as well as an "Unquenchable Flames" debuff that hops from person to person, dealing about 9000 unmitigated fire damage per target. This will last until removed by a wipe, or the target is in the pool.
Pull 2: Flame Revenants - Pull and tank these separately. Try and get as much distance as you can between each one. They don't hit that hard but they do have one ability you need to very careful of: A Flaming Tornado. They will generate an animation around them and have a casting bar before it starts. During the cast all Melee except the tank should start running away from their current target. The tornadoes (they usually come one at a time but can overlap) will follow someone around the room (ala Zul'Jin). If they hit anyone they will take ~6000 damage and fly up in the air, causing extra fall damage. Stay away from the tornadoes and you'll be fine.
Pull 3: Golems - Tank and spank. Face them away from the raid so their Flame Jets only hit the tank. They can charge and knock things down, but this isn't really a concern.
You will have a few more of pull types 2 and 3 to clear before you get to Ignis.
Composition: 2 Tanks, 2-3 Healers, 5-6 DPS.
This encounter has been nerfed so hard that I doubt 2 healers would have an issue doing it anymore.
You will have the tank that is responsible for Ignis pull him and essentially drag him around in a rectangle-like path between the two pools, dropping Scorches at each of the 4 corners. Ignis hits fairly hard, and it's easy for the tank to lose a fair chunck of their health fairly quickly.
Your "add tank" (which can be anything that has the ability to taunt - event a DPS specced OT) will be responsible for taunting the adds and keeping them in the Scorches (giant pillars of flame) until they get 10 stacked debuffs on them (they get 1/second) which causes them to go molten. After which this tank will have to smack the add a couple times and drag it off to one of the pools to be shattered. The Scorches do basically no damage and can be easily healed if this tank has to stand in it.
You will need to have 1 DPS capable of high crits (Typically a caster) available to break the golem adds once they are frozen. They need to be hit with a 5000 damage crit to explode. If you can't pull this off things will get messy very quickly.
There are several abilities you need to be aware of for Ignis:
Flame Jets - Flame Jets appear under most of the raid (it might be a radius thing, as I hardly ever got hit with them being the add tank) which will interrupt casting and lock casters out of that school for 8 seconds. There will be a warning on the screen so just don't cast when it's up there. Victims will also take around 7-8k fire damage plus a little bit from falling.
Slag Pot - Grabs a random person that is not being attacked by an add or MT and throws them in the pot chained to his belly. They will take a high amount of fire damage while they are in there for 10 seconds. However abilities to mitigate this damage can be used and healers can heal themselves if they are in the pot.
Scorch - Shoots flames from his fists to make a giant pillar of flame. Goes away after a while (you will never have more than 3 up at once). Stay out of the fire.
After the latest round of nerfs this fight is stupid easy. We got so bored our MT was trying to correct the angles on his kite path to 90 degrees. There is no enrage timer but with 5.5 mil health it shouldn't be longer than 6-7 minutes.