I think that Eliezer's survival is courageous. I realize that the standard of mere survival might not fit the traditional definition of "courage," but the Holocaust ends up inverting and subverting much in way of common language. To simply endure such an intense moment of horrific proportions is courageous. To this end, Eliezer is courageous because of his will to survive. It is difficult to comprehend that he is a teenager when the narrative unfolds. For someone of his young age to bear witness to what he saw and experienced, and to fight through that to survival is courageous. While Eliezer did not lead a rebellion or some type of large scale resistance, I think that the struggle or will to live in the conditions of the camps is an element of courage that is firmly embedded in his character. This might be how he shows courage. Eliezer does not show it as an example for others, and he does not seek to lead others in this setting. Rather, he lives and survives. In the experiences of the death camps at the zenith of the Holocaust, this constitutes as courage embodied.
In Night we see how Eliezer changes from young innocent boy to a young man who has seen the worst that humanity has to offer. Eliezer's strength can be seen as courage. It is not the physical strength, but rather his internal strength. Eliezer has to dig deep down within himself to find a way to survive. There are moments in the book when Eliezer does things that make the reader question his courage, but one does not know what one would do if one were forced to face these horrendous things. The fact that Eliezer comes out alive is courage. The fact that Eliezer didn't leave his father's side, although he wanted to so many times, show courage. Eliezer walked away from the concentration camps a changed man. He will never once be the innocent young boy he once was; he has seen too much, but he has a better understanding of faith and love and forgiveness. The fact that Eliezer didn't let hate rule his life is the truest act of courage one can have.