Use same symlink logic for stderr as stdout

This simplifies the default command by taking advantage of the default configuration just like the precedent set for access.log.

Author: tianon

Dockerfile

@@ -6,8 +6,9 @@ RUN apt-key adv --keyserver pgp.mit.edu --recv-keys 573BFD6B3D8FBC641079A6ABABF5
 RUN echo "deb http://nginx.org/packages/mainline/debian/ wheezy nginx" >> /etc/apt/sources.list
 RUN DEBIAN_FRONTEND=noninteractive apt-get update && DEBIAN_FRONTEND=noninteractive apt-get install -y nginx
 
-# forward request logs to docker log collector
+# forward request and error logs to docker log collector
 RUN ln -sf /dev/stdout /var/log/nginx/access.log
+RUN ln -sf /dev/stderr /var/log/nginx/error.log
 
 # be backwards compatible with pre-official images
 RUN ln -sf ../share/nginx /usr/local/nginx
@@ -17,4 +18,4 @@ VOLUME ["/etc/nginx"]
 
 EXPOSE 80 443
 
-CMD ["/usr/sbin/nginx", "-c", "/etc/nginx/nginx.conf", "-g", "daemon off; error_log /dev/stderr warn;"]
+CMD ["/usr/sbin/nginx", "-c", "/etc/nginx/nginx.conf", "-g", "daemon off;"]