Been there.
I recommend your warlock get fully improved voidwalker talent early on, and possibly improved health funnel. Big Blue is a very serviceable tank. Too bad you didn't pick ORC warlock, as that's the cool race and only true race for locks, but more importantly that's about 5% less aggro from the pet using Undead (+5% melee damage from orc racial command). Note: There are videos of voidwalkers tanking MC giants, and I've personally had him tank various lower instance bosses up to Baron Riverdare in Stratholme and Scholomance's Rattlegore and Alexi Barov. Kool-aid demon can really soak it up from the nastiest of enemies.
Oh! If style is your objective, have your warlock play with improved firestone and a thrash blade. WAR-locks gotta be a swashbuckler. Admiral hats for all, when you can wear them.
I recommend your warlock get fully improved voidwalker talent early on, and possibly improved health funnel. Big Blue is a very serviceable tank. Too bad you didn't pick ORC warlock, as that's the cool race and only true race for locks, but more importantly that's about 5% less aggro from the pet using Undead (+5% melee damage from orc racial command). Note: There are videos of voidwalkers tanking MC giants, and I've personally had him tank various lower instance bosses up to Baron Riverdare in Stratholme and Scholomance's Rattlegore and Alexi Barov. Kool-aid demon can really soak it up from the nastiest of enemies.
Oh! If style is your objective, have your warlock play with improved firestone and a thrash blade. WAR-locks gotta be a swashbuckler. Admiral hats for all, when you can wear them.