Smaller, based on latest Alpine.

Fixing also warning as in issue #15.

Dockerfile

@@ -1,26 +1,21 @@
-# Note: The newer busybox:glibc is missing libpthread.so.0.
-FROM busybox:ubuntu-14.04
+FROM alpine:3.7
 MAINTAINER Werner Beroux <werner@beroux.com>
 
-# Install ngrok (latest official stable from https://ngrok.com/download).
-ADD https://bin.equinox.io/c/4VmDzA7iaHb/ngrok-stable-linux-amd64.zip /ngrok.zip
 RUN set -x \
+    # Install ngrok (latest official stable from https://ngrok.com/download).
+ && apk add --no-cache curl \
+ && curl -Lo /ngrok.zip https://bin.equinox.io/c/4VmDzA7iaHb/ngrok-stable-linux-amd64.zip \
  && unzip -o /ngrok.zip -d /bin \
- && rm -f /ngrok.zip
+ && rm -f /ngrok.zip \
+    # Create non-root user.
+ && adduser -h /home/ngrok -D -u 6737 ngrok
 
 # Add config script.
 COPY ngrok.yml /home/ngrok/.ngrok2/
 COPY entrypoint.sh /
 
-# Create non-root user.
-RUN set -x \
- && echo 'ngrok:x:6737:6737:Ngrok user:/home/ngrok:/bin/false' >> /etc/passwd \
- && echo 'ngrok:x:6737:' >> /etc/group \
- && chown -R ngrok:ngrok /home/ngrok \
- && chmod -R go=u,go-w /home/ngrok \
- && chmod go= /home/ngrok
-
 USER ngrok
+ENV USER=ngrok
 
 EXPOSE 4040