How JavaScript Works: Deploying a Nodejs application with Kubernetes

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SessionStack Blog

8 min readSep 28, 2022

This is post # 73 of the series, dedicated to exploring JavaScript and its building components. In the process of identifying and describing the core elements, we also share some rules of thumb we use when building SessionStack, a JavaScript tool for developers to identify, visualize, and reproduce web app bugs through pixel-perfect session replay.

Introduction

With the recent rise in the adoption of microservice architecture, we have seen more containers being used. With that, these containers might range to hundreds and even thousands of them. It is either mismanaged or impossible to manage that amount of containers. Traditionally, you could use Docker-compose to manage several containers simultaneously but this is not feasible if you have a lot of containers with much traffic and downtime.

This brings about a container orchestration — Kubernetes. There are a few alternatives to Kubernetes which are AWS EKS, GKE, Docker-compose, etc.

In this article, we will be looking at how to deploy a Nodejs application to Kubernetes. We will be looking at a brief overview of how Kubernetes works, build a simple web server, choose an image with Dockerfile defined, build the image and push it to a registry. After that is done, we define the Kubernetes Deployment object.

Prerequisites

Docker should be installed on your system
A Docker hub account is required
Nodejs should be installed on your system
Minikube should be installed on your system
Knowledge of Javascript and Nodejs is required
Prior knowledge of Kubernetes is a plus but not necessary

Kubernetes and a brief overview

A clear definition of Kubernetes is that it is a container orchestration tool that helps manage and organize your containerized microservices while scaling them. At scale, we mean horizontal/vertical scaling, auto-healing, load-balancing — high availability, and disaster recovery — rollbacks. The first thing we need to ponder with is our containers. These containers are more or less isolated and need to be properly managed; load balanced, distributed, and connected to the outside world.

Take Kubernetes as a captain on a ship that manages both the ship and the containers on it. It can identify each container on its ship by a label referred to as a “nametag”, thereby querying it using that nametag. On the ship, the container might have to be placed inside a “Pod” which can hold some containers that are related. These Pods are the smallest units in Kubernetes(our ship) and they’re executable i.e they can run the containers in them.

In Kubernetes, each of these Pods can decide to replicate themselves, the replicated pods can be more or less but they must be running at every point in time. This management can only be done by the Replication Controller. It handles monitoring, manages the Pods lifecycle, has a template for each of the Pods which can help replicate them, and can scale the Pods horizontally and vertically.

Also, Kubernetes has what is called ‘Service’ which acts as a bridge between the Pods in a Node. With this, Pods can discover other Pods. Let’s take, for example, a file-compressor backend service with 3 replicas; do not forget these backend servers are containerized each and inside a Pod, the frontend doesn’t know which Pod it is but the Service handles the load balancing for that.

To summarize this so we go into the main reason for this article, these are the important Kubernetes vocabulary:

Node

It runs the Pods
Communicates with the master
Has a kubelet

Pods

Are within a Node
Executes the containers in it
Has 1+ containers in it

Services

Load balances
Provides communication and discovery with other Pods
Identifies Pods using a layer selector

Deployment

Indicates how many pods should run simultaneously
Manages Pods in case any dies

Building a simple Nodejs server

We are on our way to deploying a Nodejs server to Kubernetes, but the first thing we have to do is to build a simple application.

The first step is to create a project folder, and from the project folder, create a new Nodejs application using this command:

In the root directory, create an index.js file, and install the needed nodejs package by running:

Next, in our `index.js` file, we create a simple server that will only return ‘Kubernetes Deployment” as text.

Update the scripts section of your package.json file should look like this:

Now, by running `npm start` your server should be started and ready to be in a Docker container.

Containerized server

Since we will be using Docker for this, I assume you have it installed, but if not, please follow these guidelines to install Docker.

And to dockerize our app, create a Dockerfile in the root directory by running this command:

In our Dockerfile, there are a few things we will need to define and the first and most important one is the docker image. Since we are using Node for this application, our image will be based on node:

If you noticed, we used the node:18-buster-slim node image in the code above, but this can be any image of your choice. It doesn’t matter here now.

Next, we define an app directory in our container /usr/src/app, The directory could be anything but it is common to define it inside the /usr directory.

And, we use a wildcard to copy all files that are .json so it covers the package.json and package-lock.json.

Furthermore, we install dependencies and copy all files in our local directory into our container. Do not forget to create a .dockerignore file to ignore huge folders like node_modules.

Lastly, we expose the port 8080 and set the base command.

Following this, we will build the application. But before building the application, log into your docker hub account and create a new Docker hub repository called kubernetes_deploy. Then you can build the Docker image by running:

Note: use your docker hub account, not mine(vectormike) to build your docker file.

When this is successful, you can run the image that your application the container works:

Finally, push this image to your docker hub so it is accessible in Kubernetes:

If you are still unfamiliar with the above process, please refer to this guide on how to dockerize a Nodejs application.

Deployment with Kubernetes

For the sake of learning how to deploy to Kubernetes, we will have to use minikube for this. Minikube is typically meant for testing and running locally on your system. It helps you create a single node cluster inside a VM on your machine rather than a production-ready master node. It is equally easy to set up using its documentation.

Our first step here is to create a deployment.yaml file in the root directory and define our resource for deployment in the YAML file.

So, this file will contain the desired Deployment state for our application. So, if the desired state is 2 — — which is two Pods, and one of the Pods dies, it creates a new one automatically to replace it.

Also, the Service definition in the deployment.yaml file above is to enable communication between each pod and outside the cluster.

So, in our deployment.yaml file, our Service and Deployment definition will look like this:

Lastly, we deploy using the command:

As I stated earlier, our deployment will be in two parts: Services and Deployment.

The Deployment section states that we want five replicas of the Pod specified in specs.replicas with the first Pod as a template.

Inside of those Pods, we have our single container that contains our Nodejs application, and it is going to pull that image from the docker hub and run it — exposing port 8080:

In the Service section, we declare the name of the service and select the app from the `Deployment` section we defined for it to be accessible from the cluster. So in summary, our service is going to target the Pod myapp:

The ports are where it is a little bit confusing But, we are using a LoadBalancer, and within the cluster, each Pods are accessible using port: 8080 that will then target the port: 80. So for us to access the cluster from outside, we use the nodePort: 30001.

Let’s access our service using this command:

It should display the URL you will have to access from your browser.

Minikube also provides a GUI to view stats and anything else rather than using the API service or Command line. To do so, run this command:

Conclusion

This article taught us how to deploy a simple Nodejs application with Kubernetes. This is pretty basic just to give you an overview of Kubernetes and deployment is configured. In another article, we will look at how to deploy the same Nodejs application which has a database, and more about volumes in Kubernetes.

You have to be very careful when you use Kubernetes and minikube because the implementation can be tricky.

So even if you feel like the proper decisions have been made, it’s always necessary to verify that this is indeed true and your users have a great experience with your product.

A solution like SessionStack allows us to replay customer journeys as videos, showing how our customers experience our product. We can quickly determine whether our product is performing according to their expectations or not. In case we see that something is wrong, we can explore all of the technical details from the user’s browser such as the network, debug information, and everything about their environment so that we can easily understand the problem and resolve it. We can co-browse with users, segment them based on their behavior, analyze user journeys, and unlock new growth opportunities for our applications.

There is a free trial if you’d like to give SessionStack a try.