Writing a Kubernetes Operator — Locust Operator

In my previous article, I discussed how two frameworks can be used to generate the basic structure for a Kubernetes Operator. In this article I would discuss how to build on top of the base generated by the framework, so let’s go through how to build an operator with simple functionality. If you don’t know about Kubernetes operators check out the session where I talked about extedin detail.

I will be building an operator for Locust. Locust is a framework for load testing written in python. It is easy to use and supports distributed mode for simulating a higher load. But running locust in distributed mode needs more effort and a good understanding of infrastructure.

Main functions expected from Locust Operator:

• Deploy locust in standalone mode
• Deploy locust in distributed mode
• Create Kubernetes Deployments and Services
• Number of slaves can be customized

Generate Resources

operator-sdk new locust-operator --repo=github.com/amila-ku/locust-operator
operator-sdk add api --api-version=locustload.cndev.io/v1alpha1 --kind=Locust

Defining the API of Locust custom resource.

type definitions are created under pkg/api/locustload/v1alpha1/ in locust_types.go file, struct is already generated by operator SDK with a default value but I would replace with values for our locust operator.

LocustSpec directly relates to the configurable fields we want to have in our Custom Resource Definition(CRD). I defined variables for configurations required to run locust.

• HostURL: URL of the load tested service
• Image: docker image which contains locust scripts
• Users: Number of users locust should generate
• Workers: Number of workers locust should create

Generate CRDs and manifests

operator-sdk generate k8s; operator-sdk generate crds

Add the controller

operator-sdk add controller --api-version=locustload.cndev.io/v1alpha1 --kind=Locust

Modify the reconcile loop

All controllers have the Reconcile() function, this is where controller continuously check the state of resources and tries to maintain the desired specification. lets add a new deployment for locust master.

now let’s implement the deploymentForLocustO() function. This handles the creation of a Kubernetes deployment for locust master. Since locust only requires a single master this would not be user-modifiable. Container image and Target host URL is derived from the custom resource definition. Locust port 8089 is exposed together with 5557,5558 for locust workers.

Now we can build the project if everything is correctly added we would be able to generate a docker image with our changes. The image has to be pushed to a public docker registry so we can use it later.

operator-sdk build amilaku/locust-operator:v0.0.1
docker push amilaku/locust-operator:v0.0.1

then the operator.yaml has to be updated with a new image

sed -i 's|REPLACE_IMAGE|amilaku/locust-operator:v0.0.1|g' deploy/operator.yaml

then install the dependencies required

kubectl create -f deploy/service_account.yaml
kubectl create -f deploy/role.yaml
kubectl create -f deploy/role_binding.yaml
kubectl create -f deploy/operator.yaml

install operator and create CRD

kubectl create -f deploy/operator.yaml
kubectl create -f deploy/crds/locustload.cndev.io_locusts_crd.yaml

now create the Custom Resource

kubectl create -f deploy/crds/locustload.cndev.io_v1alpha1_locust_cr.yaml

output

:~$ zk get locusts
NAME             AGE
example-locust   26d
:~$ zk get pods | grep -i locust
example-locust-5c55878467-hvqjl          1/1     Running   7          26d
locust-operator-697b767b6b-zwtvl         1/1     Running   7          26d

Additional Thoughts:

What I have shown so far is just creating a deployment with an operator created using the operator framework. This only completes the requirement to perform a standalone deployment of Locust. Locust Operator which can create distributed deployments with workers is available here https://github.com/amila-ku/locust-operator. Feel free to try it out and create an Issue/PR.

Related Articles: https://medium.com/devops-srilanka/writing-a-kubernetes-operator-2c7201c6745c

More about Operators: https://www.youtube.com/watch?v=zT7CHpHy1Oc&t=3684s

If this post was helpful, please click the clap 👏 button below a few times to show your support for the author! ⬇