Flask-k8s Charm Tutorial

What You’ll Do

In this tutorial, we’ll work on:

• Constructing a Flask container
• Deploying the flask-k8s charm

The flask-k8s charm simplifies the deployment of scalable Flask applications, in addition to facilitating charm operation by interfacing with the Canonical Observability Stack (COS). We’ll guide you step-by-step through the entire deployment process to set up a basic Flask deployment.

Prerequisites

For deploying the flask-k8s charm, ensure you have a juju installation bootstrapped with any kubernetes controller. To bootstrap your juju installation with microk8s, refer to the microk8s installation documentation.

Setting up a Tutorial Model

To manage resources effectively and to separate this tutorial’s workload from your usual work, we recommend creating a new model using the following command.

juju add-model flask-tutorial

Building the Flask Container

Unlike some other Kubernetes charms, the flask-k8s charm operates in a ‘bring your own container’ mode, meaning it doesn’t provide a workload container. A container image for use with the flask-k8s charm must meet the following requirements:

• It should have gunicorn installed as a global Python package
• The Flask application should be situated in the /srv/flask/app directory
• The Flask WSGI application should be located at /srv/flask/app/app.py, with the variable name app
• The Flask application must invoke app.config.from_prefixed_env() to receive configuration

The flask-k8s repository offers a sample rockcraft project to guide you in building a compliant OCI image for the flask-k8s charm.

After creating the Flask application image, upload it to a container registry. For guidance on using microk8s’ built-in registry, refer to this online guide.

Deploying the flask-k8s charm

To deploy the flask-k8s charm from the edge channel, use the command below:

juju deploy flask-k8s --channel edge --resource flask-app-image=localhost:32000/flask-app:test 

To monitor your deployment progress across various stages, use this command:

juju status --color --watch 2s

At this point, you can access your Flask application at http://<UNIT_IP>:8000.

Cleaning up the Environment

Well done! You’ve successfully completed the flask-k8s tutorial. To remove the model environment you created during this tutorial, use the following command.

juju destroy model flask-tutorial -y