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In this post we are going to highlight the differences between Kubernetes normal service and StatefulSet service dns within the k8s cluster's context.It is important to note that the purpose of a Kubernetes service is to route traffic to specific pods that are selected by the labels. In short a service exposes pods which are selected through corresponding labels. Read more about services from the <a target="_blank" rel="noreferrer noopener" href="https://kubernetes.io/docs/concepts/services-networking/service/" alt="documentation">documentation</a>.<h2>Normal Service DNS</h2>When we say a normal service in this post we refer to the services that you create for a pod, a deployment, an external service or even another service.Services can be accessed in the cluster using the local DNS&nbsp;which uses this format:<pre>&lt;service name&gt;.&lt;service namespace&gt;.svc.&lt;cluster local domain&gt;&nbsp;</pre>This can be translated into something like:<pre>nginx.production.svc.cluster.local</pre><ul><li>nginx is our service name.</li><li>production is our name.</li><li>cluster.local is the cluster local domain</li></ul>The above will resolve to the Cluster IP of the service or to all the IPs of the pods selected by the service in the case of a headless service.<h2>StatefulSet Service DNS</h2>A StatefulSet works a little different from how a deployment works. It creates pods and assigns them a name and a sequence. For example assume you named your StatefulSet <code class="__se__t-code">nginx-server</code> and it has 3 replicas / 3 pods, then the pods will be named <code class="__se__t-code">nginx-server-0</code>, <code class="__se__t-code">nginx-server-1</code>, <code class="__se__t-code">nginx-server-2</code>.The above pod names are used to assign dns entries instead of using the pods ip address. Thus the service dns structure will look as follows:<pre>&lt;statefulset name&gt;-&lt;sequence number&gt;.&lt;service name&gt;.&lt;namespace name&gt;.svc.&lt;cluster local domain&gt; </pre>An example for the above would be:<pre>​nginx-server-0.nginx-server-service.staging.svc.cluster.local nginx-server-1.nginx-server-service.staging.svc.cluster.local nginx-server-2.nginx-server-service.staging.svc.cluster.local </pre>That is the quick view of the difference between the normal and StatefulSet DNS sometimes called FQDN.For more references kindly check the following documentations:<ol><li>Understand Kubernetes&nbsp;<a target="_blank" rel="noreferrer noopener" href="https://kubernetes.io/docs/concepts/services-networking/dns-pod-service/" alt="DNS for Services and Pods">DNS for Services and Pods</a>.</li><li>Read more on Kubernetes&nbsp;<a target="_blank" rel="noreferrer noopener" href="https://kubernetes.io/docs/concepts/workloads/controllers/statefulset/" alt="Stateful Sets">Stateful Sets</a>.</li></ol>Recommended books for beginners: <ul><li>Kubernetes Cookbook, 2nd Edition by Hideto S., Hui-Chuan L., Ke-Jou C. - keep a watch on new releases of the book also.</li></ul>Remember to subscribe to our&nbsp;<a target="_blank" rel="noreferrer noopener" href="https://www.youtube.com/@bloomlessons" alt="YouTube Channel">YouTube Channel</a>, and follow us on&nbsp;<a target="_blank" rel="noreferrer noopener" href="https://www.linkedin.com/company/bloom-lessons" alt="LinkedIn">LinkedIn</a>&nbsp;for similar content.​ Credits: Photo by <a href="https://unsplash.com/@growtika?utm_source=unsplash&amp;utm_medium=referral&amp;utm_content=creditCopyText">Growtika</a>

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Difference Between Normal Service And StatefulSet DNS In Kubernetes

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