Move all samples to the root dir

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

nginx-flask-mysql/README.md

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+## Compose sample application
+### Python/Flask with Nginx proxy and MySQL database
+
+Project structure:
+```
+.
+├── docker-compose.yaml
+├── flask
+│   ├── Dockerfile
+│   ├── requirements.txt
+│   └── server.py
+└── nginx
+    └── nginx.conf
+
+```
+
+[_docker-compose.yaml_](docker-compose.yaml)
+```
+services:
+  backend:
+    build: backend
+    ...
+  db:
+    image: mysql:5.7
+    ...
+  proxy:
+    build: proxy
+    ...
+```
+The compose file defines an application with three services `proxy`, `backend` and `db`.
+When deploying the application, docker-compose maps port 80 of the proxy service container to port 80 of the host as specified in the file.
+Make sure port 80 on the host is not already being in use.
+
+## Deploy with docker-compose
+
+```
+$ docker-compose up -d
+Creating network "nginx-flask-mysql_default" with the default driver
+Pulling db (mysql:5.7)...
+5.7: Pulling from library/mysql
+...
+...
+WARNING: Image for service proxy was built because it did not already exist. To rebuild this image you must use `docker-compose build` or `docker-compose up --build`.
+Creating nginx-flask-mysql_db_1 ... done
+Creating nginx-flask-mysql_backend_1 ... done
+Creating nginx-flask-mysql_proxy_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
+c65ecef87e85        nginx-flask-mysql_proxy     "nginx -g 'daemon of…"   About a minute ago   Up About a minute   0.0.0.0:80->80/tcp    nginx-flask-mysql_proxy_1
+96ccc0a5342f        nginx-flask-mysql_backend   "/bin/sh -c 'flask r…"   About a minute ago   Up About a minute   5000/tcp              nginx-flask-mysql_backend_1
+39327313a142        mysql:5.7                   "docker-entrypoint.s…"   About a minute ago   Up About a minute   3306/tcp, 33060/tcp   nginx-flask-mysql_db_1
+```
+
+After the application starts, navigate to `http://localhost:80` in your web browser or run:
+```
+$ curl localhost:80
+Hello world
+```
+
+Stop and remove the containers
+```
+$ docker-compose down
+```

nginx-flask-mysql/backend/Dockerfile

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+FROM python:3.6-alpine3.7
+EXPOSE 5000
+ENV PYTHONUNBUFFERED 1
+RUN mkdir /code
+WORKDIR /code
+ADD requirements.txt /code/
+RUN pip install -r requirements.txt
+ADD . /code/
+ENV FLASK_APP hello.py
+CMD flask run --host=0.0.0.0

nginx-flask-mysql/backend/hello.py

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+from flask import Flask
+app = Flask(__name__)
+
+@app.route('/')
+def hello_world():
+    return 'Hello world'

nginx-flask-mysql/backend/requirements.txt

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+click==6.7
+Flask==1.0.2
+itsdangerous==0.24
+Jinja2==2.10
+MarkupSafe==1.0
+Werkzeug==0.14.1

nginx-flask-mysql/db/password.txt

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+db-78n9n

nginx-flask-mysql/docker-compose.yaml

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+version: "3.7"
+services:
+  backend:
+    build: backend
+    depends_on: 
+    - db
+  db:
+    environment:
+      MYSQL_DATABASE: example
+      MYSQL_ROOT_PASSWORD_FILE: /run/secrets/db-password
+    image: mysql:5.7
+    restart: always
+    secrets:
+    - db-password
+    volumes:
+    - db-data:/var/lib/mysql
+  proxy:
+    build: proxy
+    ports:
+    - 80:80
+    depends_on: 
+    - backend
+volumes:
+  db-data: {}
+secrets:
+  db-password:
+    file: db/password.txt

nginx-flask-mysql/proxy/Dockerfile

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+FROM nginx:1.13-alpine
+COPY conf /etc/nginx/conf.d/default.conf

nginx-flask-mysql/proxy/conf

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+server {
+    listen       80;
+    server_name  localhost;
+    location / {
+        proxy_pass   http://backend:5000;
+    }
+
+}