Compose app skeletons

Signed-off-by: Anca Iordache <anca.iordache@docker.com>

samples/nginx-flask-mongo/docker-compose.yaml

@@ -0,0 +1,23 @@
+version: "3"
+services:
+  web:
+    image: nginx
+    volumes:
+      - ./nginx/nginx.conf:/tmp/nginx.conf
+    environment: 
+      - FLASK_SERVER_ADDR=backend:9091  
+    command: /bin/bash -c "envsubst < /tmp/nginx.conf > /etc/nginx/conf.d/default.conf && nginx -g 'daemon off;'" 
+    ports:
+    - 8080:80
+    depends_on:
+    - backend
+  backend:
+    build: flask
+    environment: 
+    - FLASK_SERVER_PORT=9091
+    volumes:
+    - ./flask:/src
+    depends_on:
+      -  mongo  
+  mongo:
+    image: mongo