The song you are referring to is Have You Ever Seen the Rain? (Wikipedia) by the band Creedence Clearwater Revival, written by the singer and guitarist John Fogerty.
According to Wikipedia, the meaning of the song is the breakdown of the band:
However, Fogerty himself has said in interviews and prior to playing the song in concert that the song is about rising tension within CCR and the imminent departure of his brother Tom from the band.[4] In an interview, Fogerty stated that the song was written about the fact that they were on the top of the charts, and had surpassed all of their wildest expectations of fame and fortune. They were rich and famous, but somehow all members of the band at the time were depressed and unhappy. Thus the line "Have you ever seen the rain, coming down on a sunny day".