Basics of Kubernetes

In this episode, Lois Houston and Nikita Abraham, along with senior OCI instructor Mahendra Mehra, dive into the fundamentals of Kubernetes. They talk about how Kubernetes tackles challenges in deploying and managing microservices, and enhances software performance, flexibility, and availability.   OCI Container Engine for Kubernetes Specialist: https://mylearn.oracle.com/ou/course/oci-container-engine-for-kubernetes-specialist/134971/210836   Oracle University Learning Community: https://education.oracle.com/ou-community   LinkedIn: https://www.linkedin.com/showcase/oracle-university/   X (formerly Twitter): https://twitter.com/Oracle_Edu   Special thanks to Arijit Ghosh, David Wright, Radhika Banka, and the OU Studio Team for helping us create this episode.   --------------------------------------------------------   Episode Transcript:   00:00 Welcome to the Oracle University Podcast, the first stop on your cloud journey. During this series of informative podcasts, we’ll bring you foundational training on the most popular Oracle technologies. Let’s get started! 00:26 Lois: Hello and welcome to another episode of the Oracle University Podcast. I’m Lois Houston, Director of Innovation Programs with Oracle University, and with me is Nikita Abraham, Principal Technical Editor. Nikita: Hi everyone! We’ve spent the last two episodes getting familiar with containerization and the Oracle Cloud Infrastructure Registry. Today, it’s going to be all about Kubernetes. So if you've heard of Kubernetes but you don't know what it is, or you've been playing with Docker and containers and want to know how to take it to the next level, you’ll want to stay with us. Lois: That’s right, Niki. We’ll be chatting with Mahendra Mehra, a senior OCI instructor with Oracle University, about the challenges in containerized applications within a complex business setup and how Kubernetes facilitates container orchestration and improves its effectiveness, resulting in better software performance, flexibility, and availability. 01:20 Nikita: Hi Mahendra. To start, can you tell us when you would use Kubernetes?  Mahendra: While deploying and managing microservices in a distributed environment, you may run into issues such as failures or container crashes. Issues such as scheduling containers to specific machines depending upon the configuration. You also might face issues while upgrading or rolling back the applications which you have containerized. Scaling up or scaling down containers across a set of machines can be troublesome.  01:50 Lois: And this is where Kubernetes helps automate the entire process?  Mahendra: Kubernetes is a portable, extensible, open source platform for managing containerized workloads and services that facilitates both declarative configuration and automation.  You can think of a Kubernetes as you would a conductor for an orchestra. Similar to how a conductor would say how many violins are needed, which one play first, and how loud they should play, Kubernetes would say, how many webserver front-end containers or back-end database containers are needed, what they serve, and how many resources are to be dedicated to each one. 02:27 Nikita: That’s so cool! So, how does Kubernetes work?  Mahendra: In Kubernetes, there is a master node, and there are multiple worker nodes. Each worker node can handle multiple pods. Pods are just a bunch of containers clustered together as a working unit. If a worker node goes down, Kubernetes starts new pods on the functioning worker node. 02:47 Lois: So, the benefits of Kubernetes are… Mahendra: Kubernetes can containerize applications of any scale without any downtime. Kubernetes can self-heal containerized applications, making them resilient to unexpected failures.  Kubernetes can autoscale containerized applications as for the workload and ensure optimal utilization of cloud resources. Kubernetes also greatly simplifies the process of deployment operations. With Kubernetes, however complex an operation is, it could be performed reliably by executing a couple of commands at the most. 03:19 Nikita: That’s great. Mahendra, can you tell us a bit about the architecture and main components of Kubernetes? Mahendra: The Kubernetes cluster has two main components. One is the control plane, and one is the data plane. The control plane hosts the components used to manage the Kubernetes cluster. And the data plane basically hosts all the worker nodes that can be virtual machines or physical machines. These worker nodes basically host pods which run one or more containers. The containers running within these pods are making use of Docker images, which are managed within the image registry. In case of OCI, it is the container registry. 03:54 Lois: Mahendra, you mentioned nodes and pods. What are nodes? Mahendra: It is the smallest unit of computing hardware within the Kubernetes. Its work is to encapsulate one or more applications as containers. A node is a worker machine that has a container runtime environment within it. 04:10 Lois: And pods? Mahendra: A pod is a basic object of Kubernetes, and it is in charge of encapsulating containers, storage resources, and network IPs. One pod represents one instance of an application within Kubernetes. And these pods are launched in a Kubernetes cluster, which is composed of nodes. This means that a pod runs on a node but can easily be instantiated on another node. 04:32 Nikita: Can you run multiple containers within a pod? Mahendra: A pod can even contain more than one container if these containers are relatively tightly coupled. Pod is usually meant to run one application container inside of it, but you can run multiple containers inside one pod. Usually, it is only the case if you have one main application container and a helper container or some sidecar containers that has to run inside of that pod. Every pod is assigned a unique private IP address, using which the pods can communicate with one another. Pods are meant to be ephemeral, which means they die easily. And if they do, upon re-creation, they are assigned a new private IP address. In fact, Kubernetes can scale a number of these pods to adapt for the incoming traffic, consequently creating or deleting pods on demand. Kubernetes guarantees the availability of pods and replicas specified, but not the liveliness of each individual pod. This means that other pods that need to communicate with this application or component cannot rely on the underlying individual pod's IP address. 05:35 Lois: So, how does Kubernetes manage traffic to this indecisive number of pods with changing IP addresses? Mahendra: This is where another component of Kubernetes called services comes in as a solution. A service gets allocated a virtual IP address and lives until explicitly destroyed. Requests to the services get redirected to the appropriate pods, thus the services of a stable endpoint used for inter-component or application communication. And the best part here is that the lifecycle of service and the pods are not connected. So even if the pod dies, the service and the IP address will stay, so you don't have to change their endpoints anymore. 06:13 Nikita: What types of services can you create with Kubernetes? Mahendra: There are two types of services that you can create. The external service is created to allow external users to connect the containerized applications within the pod. Internal services can also be created that restrict the communication within the cluster. Services can be exposed in different ways by specifying a particular type. 06:33 Nikita: And how do you define these services? Mahendra: There are three types in which you can define services. The first one is the ClusterIP, which is the default service type that exposes services on an internal IP within the cluster. This type makes the service only reachable from within the cluster. You can specify the type of service as NodePort. NodePort basically exposes the service on the same port of each selected node in the cluster using a network address translation and makes the service accessible from the outside of the cluster using the node IP and the NodePort combination. This is basically a superset of ClusterIP. You can also go for a LoadBalancer type, which basically creates an external load balancer in the current cloud. OCI supports LoadBalancer types. It also assigns a fixed external IP to the service. And the LoadBalancer type is a superset of NodePort. 07:25 Lois: There’s another component called ingress, right? When do you used that? Mahendra: An ingress is used when we have multiple services on our cluster, and we want the user requests routed to the services based on their pod, and also, if you want to talk to your application with a secure protocol and a domain name. Unlike NodePort or LoadBalancer, ingress is not actually a type of service. Instead, it is an entry point that sits in front of the multiple services within the cluster. It can be defined as a collection of routing rules that govern how external users access services running inside a Kubernetes cluster. Ingress is most useful if you want to expose multiple services under the same IP address, and these services all use the same Layer 7 protocol, typically HTTP. 08:10 Lois: Mahendra, what about deployments in Kubernetes?  Mahendra: A deployment is an object in Kubernetes that lets you manage a set of identical pods. Without a deployment, you will need to create, update, and delete a bunch of pods manually. With the deployment, you declare a single object in a YAML file, and the object is responsible for creating the pods, making sure they stay up-to-date and ensuring there are enough of them running. You can also easily autoscale your applications using a Kubernetes deployment. In a nutshell, the Kubernetes deployment object lets you deploy a replica set of your pods, update the pods and the replica sets. It also allows you to roll back to your previous deployment versions. It helps you scale a deployment. It also lets you pause or continue a deployment. 08:59 Do you want to stay ahead of the curve in the ever-evolving AI landscape? Look no further than our brand-new OCI Generative AI Professional course and certification. For a limited time only, we’re offering both the course and certification for free! So, don’t miss out on this exclusive opportunity to get certified on Generative AI at no cost. Act fast because this offer is valid only until July 31, 2024. Visit https://education.oracle.com/genai to get started. That’s https://education.oracle.com/genai. 09:37 Nikita: Welcome back! We were talking about how useful a Kubernetes deployment is in scaling operations. Mahendra, how do pods communicate with each other?  Mahendra: Pods communicate with each other using a service. For example, my application has a database endpoint. Let's say it's a MySQL service that it uses to communicate with the database. But where do you configure this database URL or endpoints? Usually, you would do it in the application properties file or as some kind of an external environment variable. But usually, it's inside the build image of the application. So for example, if the endpoint of the service or the service name, in this case, changes to something else, you would have to adjust the URL in the application. And this will cause you to rebuild the entire application with a new version, and you will have to push it to the repository. You'll then have to pull that new image into your pod and restart the whole thing. For a small change like database URL, this is a bit tedious. So for that purpose, Kubernetes has a component called ConfigMap. ConfigMap is a Kubernetes object that maintains a key value store that can easily be used by other Kubernetes objects, such as pods, deployments, and services. Thus, you can define a ConfigMap composed of all the specific variables for your environment. In Kubernetes, now you just need to connect your pod to the ConfigMap, and the pod will read all the new changes that you have specified within the ConfigMap, which means you don't have to go on to build a new image every time a configuration changes. 11:07 Lois: So then, I’m just wondering, if we have a ConfigMap to manage all the environment variables and URLs, should we be passing our username and password in the same file? Mahendra: The answer is no. Password or other credentials within a ConfigMap in a plain text format would be insecure, even though it's an external configuration. So for this purpose, Kubernetes has another component called secret. Kubernetes secrets are secure objects which store sensitive data, such as passwords, OAuth tokens, and SSH keys with the encryption within your cluster. Using secrets gives you more flexibility in a pod lifecycle definition and control over how sensitive data is used. It reduces the risk of exposing the data to unauthorized users. 11:50 Nikita: So, you’re saying that the secret is just like ConfigMap or is there a difference? Mahendra: Secret is just like ConfigMap, but the difference is that it is used to store secret data credentials, for example, database username and passwords, and it's stored in the base64 encoded format. The kubelet service stores this secret into a temporary file system. 12:11 Lois: Mahendra, how does data storage work within Kubernetes? Mahendra: So let's say we have this database pod that our application uses, and it has some data or generates some data. What happens when the database container or the pod gets restarted? Ideally, the data would be gone, and that's problematic and inconvenient, obviously, because you want your database data or log data to be persisted reliably for long term. To achieve this, Kubernetes has a solution called volumes. A Kubernetes volume basically is a directory that contains data accessible to containers in a given pod within the Kubernetes platform. Volumes provide a plug-in mechanism to connect ephemeral containers with persistent data stores elsewhere. The data within a volume will outlast the containers running within the pod. Containers can shut down and restart because they are ephemeral units. Data remains saved in the volume even if a container crashes because a container crash is not enough to cut off a pod from a node. 13:10 Nikita: Another main component of Kubernetes is a StatefulSet, right? What can you tell us about it?  Mahendra: Stateful applications are applications that store data and keep tracking it. All databases such as MySQL, Oracle, and PostgreSQL are examples of Stateful applications. In a modern web application, we see stateless applications connecting with Stateful application to serve the user request. For example, a Node.js application is a stateless application that receives new data on each request from the user. This application is then connected with a Stateful application, such as MySQL database, to process the data. MySQL stores the data and keeps updating the database on the user's request.  Now, assume you deployed a MySQL database in the Kubernetes cluster and scaled this to another replica, and a frontend application wants to access the MySQL cluster to read and write data. The read request will be forwarded to both these pods. However, the write request will only be forwarded to the first primary pod. And the data will be synchronized with other pods. You can achieve this by using the StatefulSets. Deleting or scaling down a StatefulSet will not delete the volumes associated with the Stateful applications. This gives you your data safety. If you delete the MySQL pod or if the MySQL pod restarts, you can have access to the data in the same volume.  So overall, a StatefulSet is a good fit for those applications that require unique network identifiers; stable persistent storage; ordered, graceful deployment and scaling; as well as ordered, automatic rolling updates. 14:43 Lois: Before we wrap up, I want to ask you about the features of Kubernetes. I’m sure there are countless, but can you tell us the most important ones? Mahendra: Health checks are used to check the container's readiness and liveness status. Readiness probes are intended to let Kubernetes know if the app is ready to serve the traffic.  Networking plays a significant role in container orchestration to isolate independent containers, connect coupled containers, and provide access to containers from the external clients. Service discovery allows containers to discover other containers and establish connections to them. Load balancing is a dedicated service that knows which replicas are running and provides an endpoint that is exposed to the clients. Logging allows us to oversee the application behavior.  The rolling update allows you to update a deployed containerized application with minimal downtime using different update scenarios. The typical way to update such an application is to provide new images for its containers. Containers, in a production environment, can grow from few to many in no time. Kubernetes makes managing multiple containers an easy task. And lastly, resource usage monitoring-- resources such as CPU and RAM must be monitored within the Kubernetes environment. Kubernetes resource usage looks at the amount of resources that are utilized by a container or port within the Kubernetes environment. It is very important to keep an eye on the resource usage of the pods and containers as more usage translates to more cost. 16:18 Nikita: I think we can wind up our episode with that. Thank you, Mahendra, for joining us today. Kubernetes sure can be challenging to work with, but we covered a lot of ground in this episode.  Lois: That’s right, Niki! If you want to learn more about the rich features Kubernetes offers, visit mylearn.oracle.com and search for the OCI Container Engine for Kubernetes Specialist course. Remember, all the training is free, so you can dive right in! Join us next week when we'll take a look at the fundamentals of Oracle Cloud Infrastructure Container Engine for Kubernetes. Until then, Lois Houston… Nikita: And Nikita Abraham, signing off! 16:57 That’s all for this episode of the Oracle University Podcast. If you enjoyed listening, please click Subscribe to get all the latest episodes. We’d also love it if you would take a moment to rate and review us on your podcast app. See you again on the next episode of the Oracle University Podcast.