Move all samples to the root dir

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

nginx-flask-mongo/README.md

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+## Compose sample application
+### Python/Flask application with Nginx proxy and a Mongo database
+
+Project structure:
+```
+.
+├── docker-compose.yaml
+├── flask
+│   ├── Dockerfile
+│   ├── requirements.txt
+│   └── server.py
+└── nginx
+    └── nginx.conf
+
+```
+
+[_docker-compose.yaml_](docker-compose.yaml)
+```
+services:
+  web:
+    build: app
+    ports:
+    - 80:80
+  backend:
+    build: flask
+    ...
+  mongo:
+    image: mongo
+```
+The compose file defines an application with three services `web`, `backend` and `db`.
+When deploying the application, docker-compose maps port 80 of the web service container to port 80 of the host as specified in the file.
+Make sure port 80 on the host is not being used by another container, otherwise the port should be changed.
+
+## Deploy with docker-compose
+
+```
+$ docker-compose up -d
+Creating network "nginx-flask-mongo_default" with the default driver
+Pulling mongo (mongo:)...
+latest: Pulling from library/mongo
+423ae2b273f4: Pull complete
+...
+...
+Status: Downloaded newer image for nginx:latest
+Creating nginx-flask-mongo_mongo_1 ... done
+Creating nginx-flask-mongo_backend_1 ... done
+Creating nginx-flask-mongo_web_1     ... done
+
+```
+
+## Expected result
+
+Listing containers must show two containers running and the port mapping as below:
+```
+$ docker ps
+CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS                  NAMES
+a0f4ebe686ff        nginx                       "/bin/bash -c 'envsu…"   About a minute ago   Up About a minute   0.0.0.0:8080->80/tcp   nginx-flask-mongo_web_1
+dba87a080821        nginx-flask-mongo_backend   "./server.py"            About a minute ago   Up About a minute                          nginx-flask-mongo_backend_1
+d7eea5481c77        mongo                       "docker-entrypoint.s…"   About a minute ago   Up About a minute   27017/tcp              nginx-flask-mongo_mongo_1
+```
+
+After the application starts, navigate to `http://localhost:80` in your web browser or run:
+```
+$ curl localhost:80
+Hello fom the MongoDB client!
+```
+
+Stop and remove the containers
+```
+$ docker-compose down
+```

nginx-flask-mongo/docker-compose.yaml

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+version: "3.7"
+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

nginx-flask-mongo/flask/Dockerfile

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+FROM python:3.7
+
+WORKDIR /src
+COPY . .
+RUN pip install -r requirements.txt
+
+CMD ["./server.py"]

nginx-flask-mongo/flask/requirements.txt

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+pymongo
+flask

nginx-flask-mongo/flask/server.py

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+#!/usr/bin/env python
+import os
+
+from flask import Flask
+from pymongo import MongoClient
+
+app = Flask(__name__)
+
+client = MongoClient("mongo:27017")
+
+@app.route('/')
+def todo():
+    try:
+        client.admin.command('ismaster')
+    except:
+        return "Server not available"
+    return "Hello fom the MongoDB client!\n"
+
+
+if __name__ == "__main__":
+    app.run(host='0.0.0.0', port=os.environ.get("FLASK_SERVER_PORT", 9090), debug=True)
+

nginx-flask-mongo/nginx/nginx.conf

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+server {
+  listen 80;
+  location / {
+    proxy_pass http://$FLASK_SERVER_ADDR;
+  }
+}