MicroServices using Docker Compose — a Tiny Demonstration

Here is a super quick way to launch two services, one running a Python based Docker Container application and the other running a Docker Container running Redis Server. Docker compose create a custom bridge network allowing these two micro services to be able to discover and each other without having to expose ports.

Here is the Dockerfile

FROM python:2.7-slim
WORKDIR /app
ADD . /app
RUN pip install --trusted-host pypi.python.org Flask Redis
EXPOSE 80
CMD ["python", "app.py"]

And here is the Python application app.py in the same folder (build context).

from flask import Flask
from redis import Redis, RedisError
import os
import socket
redis = Redis(host="redis-server", db=0, socket_connect_timeout=2, socket_timeout=2)
app = Flask(__name__)
@app.route("/")
def hello():
 try:
 visits = redis.incr("counter")
 except RedisError:
 visits = "<i>cannot connect to Redis server to count</i>"
html = "<h3>Hello World!</h3>\n" \
 "<b>Hostname:</b> {hostname}<br/>\n" \
 "<b>Visits:</b> {visits}\n"
return html.format(hostname=socket.gethostname(), visits=visits)
if __name__ == "__main__":
 app.run(host='0.0.0.0', port=80)

Note that the above application listens to port 80 which is also exposed in the Dockerfile and it expects the Redis Server’s hostname to be “redis-server” Let us test this.

Now let us create the docker-compose.yml file as below.

version: "3"
services:
  redis-server:
      image: redis:alpine
      ports:
        - "6379"
      networks:
        - mynet
    app:
      build: app
      ports:
        - "8080:80"
      networks:
        - mynet
      depends_on:
        - redis
  networks:
    mynet:

Folder/file structure should look like this and you should be the top folder which has the docker-compose.yml file.

.
├── app
│   ├── Dockerfile
│   └── app.py
└── docker-compose.yml

Let us now launch the application.

docker-compose up -d

This will build the Python application image first before creating the container and use redis:alpine image to launch the Redi-Server.

Above assumes that port 8080 is free on the host machine. Let us now test this.

curl localhost:8080
<h3>Hello World!</h3><b>Hostname:</b> b3f2f3a731a6<br/><b>Visits:</b> 1
curl localhost:8080
<h3>Hello World!</h3><b>Hostname:</b> b3f2f3a731a6<br/><b>Visits:</b> 2

Notice that our app container is able to discover the IP address of the Redis Server using the host name “redis-server” as referred in the app.py

Thanks for your time. Please follow me for more such tiny demo snippets!