A Simple Flask Web Service

A simple but flexible Flask web service used to demonstrate microservices architectures. It is designed to operate across three different containers:

• A "front-end" container that provides an HTML response based on information gathered from two "back-end" JSON-based web services
• The "user" API, which is a JSON-based web service queried by the front-end container(s)
• The "order" API, which is a JSON-based web service queried by the front-end container(s)

Usage

This web service is a single application designed to run in three separate containers.

Using Docker Compose

The easiest way to spin up the application is to use Docker Compose. A docker-compose.yml file is provided in the repository.

docker-compose up -d

Using Kubernetes

A set of YAML files for defining a Deployment and a Service for each of the three components are found in the kubernetes directory of this repository. Use kubectl to create the objects via commands such as these:

kubectl apply -f kubernetes/flask-order-api.yml
kubectl apply -f kubernetes/flask-user-api.yml
kubectl apply -f kubernetes/flask-web-ui.yml

The HTML front-end will be exposed via a cloud provider load balancer on port 5000.

Running the Containers Manually

Running the containers manually is a bit more difficult, but certainly possible.

1. First, launch the "user" API container:

    docker run -d -e PORT=6000 -p 6000:6000 slowe/flask-web-svc:latest
   

   Make note of the IP address where the container is running, as you'll need it later.

2. Next, launch the "order" API container:

    docker run -d -e PORT=7000 -p 7000:7000 slowe/flask-web-svc:latest
   

   As with the previous step, make note of the IP address where this container is scheduled.

3. Before proceeding, ensure that the back-end containers are working properly. Use curl or a web browser to access the URL for the containers:

    http://<IP address from step 1>:6000/users/json/
    http://<IP address from step 2>:7000/orders/json/
   

   You should get back a JSON-formatted response that contains information about the request. If this doesn't work, resolve the issue before continuing.

4. Finally, launch the front-end container:

    docker run -d -e USER_API_HOST=<IP address from step 1> -e USER_API_PORT=6000 -e ORDER_API_HOST=<IP address from step 2> -e ORDER_API_PORT=7000 -p 5000:5000 slowe/flask-web-svc:latest
   

   If you want the front-end container to listen on a port other than 5000, change the -p parameter and add an additional environment parameter in the form -e PORT=<desired port>.

The application is now running and ready to use. You can use curl or a web browser to access the application:

http://<IP address from step 4>:5000/

This will provide an HTML-formatted response that contains information about the request and the requests/responses from the back-end JSON-based web services. You can use this information to see how various container orchestration systems and other technologies affect the communications between containers.

License

This material is licensed under the MIT License.