In the previous blog we have seen how to create a statefulset MariaDB application. Also, we learned how replication works in MariaDB in this blog. Now, we will try to create a replicated statefulset application. As good references for creating this blog, I would like to give credit to the Kubernetes documentation as well as an example from Alibaba Cloud.
To replicate a MariaDB application we are going to create a statefulset that will consist of a single init container and one application container.
In the previous blog we created a stateless application, deployed with K8s resource Deployment, which allows one to replicate the application, but where data is lost when Pods are restarted, meaning there were no data consistency. In the same blog we used PersistentVolumeClaim for dynamic provisioning of PersistentVolume, but we used Deployment, meant for stateless application, and this way is *not recommended* for statefulset application where each replica should have its own persistent volume. The proper way to achieve that is through the Statefulset resource and this post we will cover that.
In K8s one can create a stateful application, an application like a database, which needs to save data to persistent disk storage for use by the server/clients/other applications, to keep track of its state and to be able to replicate and be used in distributed systems.
In the previous blog, MariaDB & K8s: Create a Secret and use it in MariaDB deployment, we used the Secrets resource to hide confidential root user data, and in the blog before that in the series, MariaDB & K8s: Communication between containers/Deployments, we created 2 containers (namely MariaDB and phpmyadmin) in a Pod. That kind of deployment didn’t have any persistent volumes.
In this blog we are going to create separate Deployments for MariaDB and WordPress applications as well as a Service for both in order to connect them. Additionally we will create Volume in a Pods of a MariaDB Deployment.
In the previous blog we created a stateless application, deployed it with K8s resource Deployment, and exposed the root password, which, regarding security, is of course not recommended. K8s allows one to hide confidential data using specific K8s resources.
Let’s see how to use Secrets in K8s.
In order to save confidential data one can use a K8s resource called Secret.
One can create Secret from the CLI by running kubectl create secret.
Here we will use two methods to create the secret.
In this blog we are going to proceed to create the frontend container to communicate with the backend through a Service and other resources.
When an application is run through the Deployment Pods are created and destroyed dynamically. When created, they get the internal IP address in a cluster, and since they are ephemeral, there needs to be a stable way to allow communications between Pods.
This is the first in a series of blogs explaining how to use MariaDB in Kubernetes (K8s), as well as explaining some important concepts of K8s and of MariaDB.
This blog explains how to start MariaDB as a stateless application in K8s using the CLI and explores different commands you can run on your CLI.
Let’s first start the minikube
$ minikube start && kubectl get nodes
NAME STATUS ROLES AGE VERSION
minikube Ready control-plane,master 104d v1.22.2
The Pod is a K8s resource and the smallest unit in K8s.