Support deploying app to custom context

Dockerfile

@@ -10,4 +10,7 @@ VOLUME ["/var/lib/h2/", "/tomcat7"]
 
 ADD http://atc.gd/docker-registry-ui.war /tomcat7/webapps/ROOT.war
 
-CMD sed -i '1iexport CATALINA_OPTS=" -Djava.security.egd=file:/dev/./urandom "' bin/catalina.sh && bin/catalina.sh run
+ADD startup.sh /tomcat7/startup.sh
+
+CMD /tomcat7/startup.sh
+

README.md

@@ -32,6 +32,12 @@ This project is containerized. You can run with docker right now by simply runni
 
 and browsing to localhost:8080/.
 
+## Application context
+
+Sometimes you may want to run the app in custom context, say `http://server:8080/webui`. To do so, supply the optional variable `APP_CONTEXT`.
+
+	docker run -p 8080:8080 -e APP_CONTEXT=/webui atcol/docker-registry-ui
+
 ## Statelessness
 
 The app' requires registry configuration which can be supplied once the app's running, or through container environment

startup.sh

@@ -0,0 +1,6 @@
+if [ -n "$APP_CONTEXT" ]; then
+  mv /tomcat7/webapps/ROOT.war /tomcat7/webapps/${APP_CONTEXT}.war
+fi
+sed -i '1iexport CATALINA_OPTS=" -Djava.security.egd=file:/dev/./urandom "' bin/catalina.sh
+bin/catalina.sh run
+