who composed it?
Lady Gaga, Fernando Garibay, and DJ White Shadow
The Edge of Glory
"The Edge of Glory" was written by Lady Gaga, Fernando Garibay, and DJ White Shadow, and was produced by Gaga and Garibay. 
what is the song edge of glory about It speaks of the very last moments of life.
wiki:20812330
The Edge of Glory [SEP] Background and release
"The Edge of Glory" was written by Lady Gaga, Fernando Garibay, and DJ White Shadow, and was produced by Gaga and Garibay. The origins of the song first came about in January 2011, when Gaga released part of the lyrics on her Twitter account. White Shadow revealed that before they returned to Europe for the 2010 dates of The Monster Ball Tour, Gaga had taken leave for few days to be with her ailing grandfather. After he died, Gaga told White Shadow that she wrote a song about her grandfather's death and its impact on her. Gaga spoke to Jon Pareles of "The New York Times" about the story behind the song: "['The Edge of Glory'] was about how when my grandma was standing over my grandfather while he was dying.