Two days ago I gave a small talk in the DJUGL (Django User Group London) explaining how we could deploy a test application into Kubernetes. This post is going to explain something pretty similar, how to deploy a Flask app into Kubernetes and how to rolling update it.
Before starting, you can find all the materials of this post in my k8s-py-example repo.
Download the app and build it twice, one for each of the version that you want to deploy. This versions will need to be tagged properly and sent to Docker Hub. Basically the steps to follow are:
docker build -t agonzalezro/k8s-py-example . docker tag agonzalezro/k8s-py-example:latest agonzalezro/k8s-py-example:0.1 # Change the code (src/app.py) a little bit to see the differences docker build -t agonzalezro/k8s-py-example . docker tag agonzalezro/k8s-py-example:latest agonzalezro/k8s/py-example:0.2 docker push agonzalezro/k8s-py-example
Now that all the work related with Docker is done, let’s take a look to the needed k8s files:
rc files are the definitions of your replication controllers, one of them using the version
0.1 and the other the image
0.2. The service file is share since the application is going to be the same.
Let’s run the first version of the app:
kubectl -f rc-0.1.yml -f service.yml --validate=false # The validate tag is just needed because of a bug in current k8s
Now, if you do
kubectl get services you will see the external IP of your service. You can use it to check that it’s running and showing the code of the version
Cool! You have deployed your first k8s application, now, let’s update it:
kubectl rolling-update flaskapp-rc -f rc-0.2.yml
If you wait a little bit you will see in the logs what’s happening there. Let the command finish and you will have your
0.2 version deployed having causing 0 downtime!
As always, feel free to contact me here or use twitter: @agonzalezro