Made the upstream host/port a environment variable

docker-compose.yml

@@ -14,3 +14,6 @@ nginx:
         - appdata
     ports:
         - 80:80
+    environment:
+    - UPSTREAM_HOST=fpm
+    - UPSTREAM_PORT=9000

nginx/Dockerfile

@@ -1,3 +1,9 @@
 FROM nginx:1.9
 
 COPY nginx.conf /etc/nginx/conf.d/app.conf
+
+CMD /bin/bash -c envsubst < /etc/nginx/conf.d/app.conf.template > /etc/nginx/conf.d/app.conf && nginx -g 'daemon off;'
+
+CMD sed -i 's/UPSTREAM_HOST/'"$UPSTREAM_HOST"'/g' /etc/nginx/conf.d/app.conf \
+ && sed -i 's/UPSTREAM_PORT/'"$UPSTREAM_PORT"'/g' /etc/nginx/conf.d/app.conf \
+ && nginx -g 'daemon off;'

nginx/nginx.conf

@@ -36,7 +36,7 @@ server {
 	location ~ \.php$ {
         try_files $uri =404;
 		fastcgi_split_path_info ^(.+\.php)(/.+)$;
-		fastcgi_pass  fpm:9000;
+		fastcgi_pass  UPSTREAM_HOST:UPSTREAM_PORT;
 		fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
         fastcgi_param SCRIPT_NAME $fastcgi_script_name;
 		fastcgi_index index.php;