The main purpose of this project is provide a method to create a scalable API using R. The easiest way to create a API in R is using Plumber package https://cran.r-project.org/web/packages/plumber/index.html

If you are used this package you probably know that by default, plumber allows you to create a synchronous API. This is a serious problem if you want to use it in a production environment. There are probably many methods to avoid this, in this project I'm going to use Docker and Kubernetes for trying to fix this problem.

To use a real model, we can create it with the popular dataset mtcars. The objective is not create a great model, we are just doing it to simulate a real situation of a ML model doing predictions via API.

Execute this command to create the object RfModel.RDS. I recommend trimmer package (https://cran.r-project.org/web/packages/trimmer/index.html) to simplify your ML model.

Rscript ./R/createModel.R

• I will use a previous image of R (3.5.0). To pull this image run:

docker pull rocker/r-ver:3.5.0

• Now we can create our docker container with our Plumber API. Necessary information to build the container is in ./Dockerfile

docker build -t plumber-example .

To run our container we just have to execute:

docker run --rm -p 8000:8000 plumber-example

If everything is working correctly you should see something like this:

It's time to use our API to make predictions, if you run the next command you have to receive: ["6"], the prediction of our Random Forest model.

curl -d '{"data":{"mpg":21,"disp":160,"hp":100,"drat":3.9,"wt":2.62,"qsec":16.46,"vs":0,"am":1,"gear":4,"carb":4}}' http://127.0.0.1/prediction

Nice, we can use our model but what happen if we do this request first and immediately we try to make a prediction? Our prediction will need five seconds...

curl http://127.0.0.1/asynchronousTest

If we go to the file ./R/PredictRf we can check that asynchronousTest just wait 5 seconds and return "OK". We can use this function to check that our API is synchronous for now.

To use Kubernetes I'm going to use minikube, here you have documentation to install it: https://kubernetes.io/es/docs/tasks/tools/install-minikube/

Start our Kubernetes cluster:

minikube start
eval $(minikube docker-env)
kubectl apply -f deployment.yaml

You can check you have a pod named plumber-example-... running:

kubectl get pods --output=wide

We have to expose our service for being able to consume our API.

kubectl expose deployment plumber-example --type=LoadBalancer --name=plumber-service

Using minikube you can know ip and port of the API running

minikube service plumber-service

If you are not using minikube just execute:

kubectl describe services plumber-service

what happens if we now use our asynchronousTest to check our API? At this moment our API is still synchronous, but here is when we can use kubernetes to scale it! Execute this command and try again:

kubectl scale deployment/plumber-example --replicas=3

At this point you would have an asynchronous API thanks to Kubernetes! To check that you have three different pods running execute kubectl get pods --output=wide and you would see this:

• https://kubernetes.io/docs/tutorials/stateless-application/expose-external-ip-address/
• https://medium.com/tmobile-tech/using-docker-to-deploy-an-r-plumber-api-863ccf91516d
• https://kubernetes.io/docs/setup/learning-environment/minikube/
• https://kubernetes.io/docs/concepts/overview/working-with-objects/kubernetes-objects/