Kubernetes Replication Controller: A Complete Guide
Kubernetes is the steadiest orchestration platform to perform container automation at present. Kubernetes comes with a wide variety of usage and the platform has several properties to know about. If you want to develop and configure an application on Kubernetes, you’re supposed to get the details of the functionality and utility of the different properties of Kubernetes. When it comes to Kubernetes, the platform utilizes pods as containers to create and deploy application configurations. Here, the concept of a replication controller comes. Without the functional presence of replication controllers, the basic functions of Kubernetes will be incomplete. In this article, we will discuss everything about replication controllers to help you know them well and recognize their functions.
What are Replication Controllers?
Replication controllers can be considered the building blocks to keep an application running on Kubernetes. As you know, pods are significant in terms of continuing Kubernetes functions; replication controllers manage pods. To be specific, replication controllers indulge in monitoring the life spans of pods and their replicas.
The basic task of replication controllers is to make a specified number of pods and their replicas available for usage on the Kubernetes network. A replication controller controls the number of replicas of a pod that are present in a particular Kubernetes cluster. Whenever a pod gets terminated, the replication controllers create a replica of that particular pod immediately to avoid functional failure of that cluster.
When the number of pods in a Kubernetes cluster exceeds the requirement, replication controllers actively take part in eliminating extra pods. Contradictorily, replication controllers get involved in creating new pods when the number of pods available in a cluster is lesser than the requirements.
Also, another major responsibility of a replication controller is to add additional features and functionalities to a pod from which multiple replicas are created. Therefore, the significance of replication controllers in the basic functions of Kubernetes can’t be overlooked at all.
Uses of Replication Controllers
Firstly, rescheduling the creation of replicas of pods is one of the most important tasks of replication controllers. Replication controllers keep rescheduling replica creation according to the requirements so that the cluster never runs out of an adequate number of pods. Therefore, the functional tasks of Kubernetes keep going on without any interruption. Replication controllers keep clusters running even during node failures or unwanted pod termination.
Pods and their replicas are highly scalable and replication controllers remain liable to scale replicas up and down in a Kubernetes cluster. Generally, replication controllers do so with the help of auto-scaling agents. However, sometimes the user can scale replicas up or down manually.
Controlling rolling updates is another major task of replication controllers. Without rolling updates, the pods in a Kubernetes cluster won’t work as they are supposed to do. So, replication controllers are mentionable contributors behind monitoring and scaling the rolling updates for enhancing the functions of a specific cluster.
On top of that, replication controllers remain liable for releasing multiple release tracks and monitoring them over a prolonged period. Most importantly, replication controllers can utilize all the release tracks of a cluster simultaneously.
When to Use Replication Controllers?
Before using replication controllers for pod orchestration, you are supposed to keep in mind that they monitor and replicate live pods only. Replication controllers don’t count terminated pods. So, you can’t determine the liveliness or readiness of pods when you’re using a replication controller. You are supposed to keep this fact in mind to manage your Kubernetes pods promptly. If you want to manage existing pods and determine the readiness probes of terminated pods collaterally, you need to use other advanced tools along with replication controllers to get your job done.
Commands Required for Handling Replication Controllers
You’ve already gathered adequate information about replication controllers and their functions. Now, it’s time to check out the specified kubectl commands that are required for handling replication controllers.
First of all, you need to create a replication controller to make use of it. Use the following kubectl command to make that possible:
kubectl create -f nginx-rc.yml
The following command enabled you to deploy the replication controller in the system:
kubectl get rc/nginx-rc
kubectl get rc/nginx-rc -o wide
kubectl get rc/nginx-rc -o yaml
kubectl get rc/nginx-rc -o json
As you deploy a replication controller in a cluster, you are supposed to describe it for identification purposes. Input the following command to describe the replication controller you created:
kubectl describe rc/nginx-rc
Now, you may be curious about how you can scale up the replicas of your pods with the help of a replication controller. As you have already created and deployed one in your cluster, input the following command to scale up and manage existing pods:
kubectl scale rc nginx-rc –replicas=5
Sometimes you may need to delete a replication controller when it is of no use anymore. This is mainly applicable for application-specific replication controllers. To delete a replication controller, the commands are:
- kubectl delete rc nginx-rc
- kubectl delete -f nginx-rc.yml
These are the kubectl commands to handle replication controllers and make them work. However, as you gain expertise in handling replication controllers, you will learn to use them for different purposes. There are more commands for advanced users to perform different tasks with replication controllers. But as a beginner, the commands mentioned above are enough for you to manage replication controllers.
Alternatives to Replication Controllers
Though the utility of replication controllers is beyond question, there are other options to manage pods efficiently. The following segment will let you know about the great alternatives of replication controllers with which you can manage your pods efficiently.
ReplicaSets can be considered the upgraded versions of conventional replication controllers. ReplicaSets have enabled set-based label selectors which help users to orchestrate their pods in customized ways. In most cases, ReplicaSets are not directly utilized for pod management as they are a bit hard to handle. Ideally, Deployments enforce ReplicaSets to orchestrate pod creations, selections, and updates. ReplicaSets are handy tools to perform customized update orchestration. With other replication orchestration tools, it’s not possible to customize orchestrations. If you are in dire need of orchestrating pod updates in customized manners, you are supposed to use ReplicaSets directly.
Deployments are exclusive high-level API objects to update pods under them. Alongside, Deployments take part in updating the existing ReplicaSets under them too. Being server-side tools, Deployments come with special features to add more functionality to your pods. Also, the declarative nature of Deployments make them the preferred choices of users.
Job is another handy alternative to replication controllers. Some Kubernetes pods tend to terminate themselves and such pods are quite hard to manage. Usually, such pods can’t be monitored and scaled by replication controllers and other tools. Job is a specified orchestration tool to manage such self-terminating pods and make the most out of them.
These are the decent alternatives to replication controllers that are very helpful in managing pods in your cluster. You’re supposed to select an orchestration tool based on your requirements. We have specified the functionalities of all the orchestration tools mentioned above. So, make the right choice and use the tool that you need to manage your pods.
The effectiveness of Kubernetes replication controllers is evident and unputdownable. This article has briefly described all the special features and functions of Kubernetes replication controllers. As a beginner, you must go through the above segments to get a clear idea of what replication controllers are and how to use them. We have already described the ways to handle Kubernetes replication controllers with specified commands. Also, we have mentioned the top alternatives to replication controllers to help readers choose the right orchestration tools for their requirements.
Now, you have got a basic idea about the functions and features of Kubernetes replication controllers. So, it’s time to imply your knowledge and use and customize replication controllers to manage your pods in the best ways. All the best!