I have hard swollen lymph node under left eye only?

Get a medical check: If you have a knot under the eye, it needs to be examined by your doctor who can then make a proper diagnosis and advise you about treatment. It is not likely to be a lymph node based on its location(lymph nodes are located in predictable sites like in front of the Ears or on your neck(not elsewhere in the area of head and Neck).

Stye?: There aren't usually lymph nodes under the eye. This may be a stye.