With the attacking king stuck in front of its own rook pawn on a7, the defender draws if his king reaches c7 (or b6) and stays there: the white king has no exit and the rook alone cannot evict the defender.
White has pushed the a-pawn to a7 and the king has gone to a8 in front of it. Against any other pawn this would be a Lucena win, but the rook pawn leaves the white king no squares: b7 and b8 are controlled by the black king on c7, and the rook on h2 keeps the king from ever leaving the corner.