There are several settings in Crazy Rich Asians.
London, England, UK
The prologue of the story occurs in a hotel in London, England. Through the interaction between the Young family and the hotel staff, we learn of the Youngs' incredible wealth and power. The setting of London only builds the sense of grandeur, as it is classically considered to be a posh, wealthy city.
New York City, NY, USA
Rachel and Nick meet in New York and live there. Rachel works as an economics professor and is highly independent, modern, and American, much like the city she lives in.
Most of the novel occurs in Singapore. It is there that we meet Nick's family and all of the wealthy, zany characters that accompany them. Wealthy Singapore is so far from what Rachel is used to in her American life that it adds to her position as a "fish out of water."