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python-asyncio-kubernetes-template

A simple example of a micro-service written using Python Asyncio and hosted on Kubernetes (Google Container Engine)

This repository has two goals:

  • Provide a complete example, and later short tutorial, on how to run a Python Asyncio based application on Kubernetes / Google Container Engine.
  • Document my current understanding of how best to structure the basics of a Python Asyncio application for use with Kubernetes. Specifically this refers to things like handling the shut down (SIGTERM) signal. It took me a while to figure this out so hopefully this example will save others time.

If you know of a better way to accomplish any of this please get in touch or submit a PR.

Not 100% Complete Tutorial

Create A Google Cloud Services Account and Google Container Engine Cluster

All of this can be done in the Google Developers Console. Google has good docs on this.

For later steps you'll need to remember the project name, region/zone name and cluster name.

Install the Google Cloud SDK

This provides the gcloud command and Kubernetes (kubectl).

gcloud components list shows which sub-components are installed. Just install all of them.

Install and start Docker on your local machine.

####Fedora

dnf install docker

systemctl start docker.service

Note that the above only starts the docker service once. You need to enable the service if you want it to start on every boot.

systemctl enable docker.service

Build the container image

This example uses a Fedora container image as the base and installs third party Python 3.5 packages because Python 3.5 is not yet available in Fedora 23. If you want to use another distribution (why would you?) just edit the Dockerfile.

While inside the repository directory:

docker build .

When complete you will be able to see the image when listing the available Docker images.

docker images

Tag the container image.

Now we need to tag the image to upload it to the Google Container Registry (GCR). Each Google Cloud project has it's own GCR name space. Replace the image ID and Google cloud project name in the example below.

docker tag -f IMAGE_ID gcr.io/PROJECT_ID/python-asyncio-kubernetes-template:latest

Push the container image to GCR.

You'll need to authenticate with Google and set the project and region/zone before this will work.

gcloud docker push gcr.io/PROJECT_ID/python-asyncio-kubernetes-template:latest

Get Cluster Credentials for Kubernetes

cloud container clusters get-credentials CLUSTER_NAME

Start the Container

kubectl create -f controller.json

Optional - Start a Service (Load Balancer)

When a replication controller and its pods are created, none of the pods are reachable. If you want to reach them you need to create a service. The example service.json file creates a load balancer service which makes the pods reachable from the Internet. If you just need them reachable within the cluster, set the type to ClusterIP.

See http://kubernetes.io/v1.0/docs/user-guide/services.html for more information.

Once the service is up you can get its IP, including the external IP Google allocates by running:

kubectl get services

Note that it seems to take a little while for the external IP address to be assigned.

Useful Commands

kubectl get rc

kubectl get pods

kubectl logs PODNAME

kubectl scale --replicas=1 replicationcontrollers python-asyncio-kubernetes-template

Also, your Docker, Kubernetes and container logs should now be available in Google Cloud Logging. The output of the containers doesn't seem to integrate very well into Cloud Logging well though (as of 2015-11).