31 Mar 2018

Deploying to K8s cluster with Fn Function

An essential step of any CI/CD pipeline is deployment. If the pipeline operates with Docker containers and deploys to K8s clusters then the goal of the deployment step is to deploy a specific Docker image (stored on some container registry) to a specific K8s cluster.  Let's say there is a VM where this deployment step is being performed. There are a couple of things to be done with that VM before it can be used as a deploying-to-kuberenetes machine:
  • install kubectl (K8s CLI) 
  • configure access to K8s clusters where we are going to deploy 
Having the VM configured, the deployment step does the following:
# kubeconfig file contains access configuration to all K8s clusters we need
# each configuration is called "context"
export KUBECONFIG=kubeconfig

# switch to "google-cloud-k8s-dev" context (K8s cluster on Google Cloud for Dev)
# so all subsequent kubectl commands are applied to that K8s cluster
kubectl config  use-context google-cloud-k8s-dev

# actually deploy by applying k8s-deployment.yaml file
# containing instructions on what image should be deployed and how  
kubectl apply -f k8s-deployment.yaml

In this post I am going to show how we can create a preconfigured Docker container capable of deploying a Docker image to a K8s cluster. So, basically, it is going to work as a function with two parameters: docker image, K8s context. Therefore we are going to create a function in Fn Project basing on this "deployer" container and deploy to K8s just by invoking the function over http.

The deployer container is going to be built from a Dockerfile with the following content:
FROM ubuntu

# install kubectl
ADD https://storage.googleapis.com/kubernetes-release/release/v1.6.4/bin/linux/amd64/kubectl /usr/local/bin/kubectl
ENV HOME=/config
RUN chmod +x /usr/local/bin/kubectl
RUN export PATH=$PATH:/usr/local/bin

# install rpl
RUN apt-get update
RUN apt-get install rpl -y

# copy into container k8s configuration file with access to all K8s clusters
COPY kubeconfig kubeconfig

# copy into container yaml file template with IMAGE_NAME placeholder
# and an instruction on how to deploy the container to K8s cluster
COPY k8s-deployment.yaml k8s-deployment.yaml

# copy into container a shell script performing the deployment
COPY deploy.sh /usr/local/bin/deploy.sh
RUN chmod +x /usr/local/bin/deploy.sh

ENTRYPOINT ["xargs","/usr/local/bin/deploy.sh"]

It is worth looking at the k8s-deployment.yaml file. It contains IMAGE_NAME placeholder which is going to be replaced with the exact Docker image name while deployment:

apiVersion: extensions/v1beta1
kind: Deployment

...

    spec:
      containers:
      - image: IMAGE_NAME
        imagePullPolicy: Always
...

The deploy.sh script which is being invoked once the container is started has the following content:
#!/bin/bash

# replace IMAGE_NAME placeholder in yaml file with the first shell parameter 
rpl IMAGE_NAME $1 k8s-deployment.yaml

export KUBECONFIG=kubeconfig

# switch to K8s context specified in the second shell parameter
kubectl config  use-context $2

# deploy to K8s cluster
kubectl apply -f k8s-deployment.yaml

So, we are going to build a docker image from the Dockerfile by invoking this docker command:
docker build -t efedorenko/k8sdeployer:1.0 .
Assuming there is Fn Project up and running somewhere (e.g. on K8s cluster as it is described in this post) we can create an Fn application:
fn apps create k8sdeployerapp
Then create a route to the k8sdeployer container:
fn routes create k8sdeployerapp /deploy efedorenko/k8sdeployer:1.0
We have created a function deploying a Docker image to a K8s cluster. This function can be invoked over http like this:
curl http://35.225.120.28:80/r/k8sdeployer -d "google-cloud-k8s-dev efedorenko/happyeaster:latest"
This call will deploy efedorenko/happyeaster:latest Docker image to a K8s cluster on Google Cloud Platform.


That's it!



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