nginx-flask-mongo: add dev envs support (#268)

Signed-off-by: Milas Bowman <milas.bowman@docker.com>

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

@@ -0,0 +1,27 @@
+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:
+      - 80:80
+    depends_on:
+      - backend
+
+  backend:
+    build:
+      context: flask
+      target: dev-envs
+    stop_signal: SIGINT
+    environment:
+      - FLASK_SERVER_PORT=9091
+    volumes:
+      - /var/run/docker.sock:/var/run/docker.sock
+    depends_on:
+      -  mongo  
+
+  mongo:
+    image: mongo