Bulb or ballast?
 

My driver side headlight will flickers for a few times and do not turn on. Do you think it is the ballast or the bulb? The light is stock, I do have 6K bulb ready to put in, but if it is the ballast, I would want to change it at the same time. Any help is appreciated.

Do anyone know if this is cover under warranty? Don't really trust my local dealer. Debating if I want to just suck it up and change the ballast and the blurbs at the same time myself.

your car's still under warranty? just take it in, or just try a new bulb to see.
not sure if considered a wear item though. if so, no warranty.

in my experience diagnosing OEM HID headlights is like this: when the light turns on and goes off after a min or two, its the bulb. If it doesn't turn on at all then would be the ballast.

Swap ballasts. If problem stay on the same side, it's the bulb. If problem moves to the other side, it's the ballast.
... or ...
Find somebody dumb enough to let you try the bulb in their car. If bulb works, you have a bad ballast. ...
... or ...
The bulb and the ballast could both be bad.

Not sure, but I think the ballast is covered under warranty but bulbs are considered a "normal wear item."

Mine is starting to do that, too, and I have Morimoto bulbs. Happens on the passenger side on some bumps. When the bulb goes out, I just turn the headlights off and back on. I plan to get new bulbs the next time I drop the bumper.