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Kubernetes Zero Downtime Deployment

Kubernetes Zero Downtime Deployment
Photo by Growtika / Unsplash

Kubernetes is an open-source container orchestration platform that automates the deployment, scaling, and management of containerized applications. One of the key features of Kubernetes is the ability to perform zero downtime deployment, which means deploying a new version of an application without causing any disruption to end-users. In this blog post, we will explore the concept of zero downtime deployment in Kubernetes and how it can be achieved.

What is Zero Downtime Deployment?

Zero downtime deployment is the process of deploying a new version of an application without causing any downtime or service interruption. This means that end-users can continue to use the application without any interruption, even while the new version is being deployed. This is particularly important for applications that require high availability, as downtime can lead to loss of revenue and customer dissatisfaction.

How Kubernetes Achieves Zero Downtime Deployment

Kubernetes achieves zero downtime deployment through a technique called Rolling Updates. Rolling Updates allow Kubernetes to deploy new versions of an application gradually, one instance at a time, while keeping the existing instances running. This means that Kubernetes can update an application without taking it offline.

Rolling Updates work by creating a new ReplicaSet with the updated version of the application and gradually increasing the number of replicas in the new ReplicaSet while decreasing the number of replicas in the old ReplicaSet. This process continues until all replicas in the old ReplicaSet have been replaced by replicas in the new ReplicaSet. Once the process is complete, the old ReplicaSet is deleted, and the new ReplicaSet takes over.

To achieve zero downtime deployment, Kubernetes uses the following steps:

  • Create a new ReplicaSet: Kubernetes creates a new ReplicaSet with the updated version of the application.
  • Gradually increase the number of replicas in the new ReplicaSet: Kubernetes gradually increases the number of replicas in the new ReplicaSet, one instance at a time.
  • Gradually decrease the number of replicas in the old ReplicaSet: Kubernetes gradually decreases the number of replicas in the old ReplicaSet, one instance at a time.
  • Verify the health of the new ReplicaSet: Kubernetes verifies the health of the new ReplicaSet to ensure that all instances are running correctly.
  • Delete the old ReplicaSet: Once the new ReplicaSet has been fully deployed and verified, Kubernetes deletes the old ReplicaSet.

Example

here's an example of how Kubernetes achieves zero downtime deployment:

                       +---+    +---+    +---+    +---+
                       |   |    |   |    |   |    |   |
Old ReplicaSet (v1)    | 1 |    | 2 |    | 3 |    | 4 |
                       |   |    |   |    |   |    |   |
                       +---+    +---+    +---+    +---+

                       +---+
New ReplicaSet (v2)    |   |
                       +---+

Let's say you have a web application running in Kubernetes with four instances, each serving user requests. You want to deploy a new version of the application without causing any downtime. Here's how Kubernetes achieves this:

  • Create a new ReplicaSet: Kubernetes creates a new ReplicaSet with the updated version of the application.
                       +---+
New ReplicaSet (v2)    | 1 |
                       +---+
  • Gradually increase the number of replicas in the new ReplicaSet: Kubernetes starts creating new instances of the updated application in the new ReplicaSet, while keeping the old ReplicaSet running. At this point, you have four instances running in the old ReplicaSet and zero instances in the new ReplicaSet.
                       +---+    +---+
New ReplicaSet (v2)    | 1 |    | 2 |
                       +---+    +---+

                       +---+    +---+    +---+
Old ReplicaSet (v1)    | 1 |    | 2 |    | 3 |
                       +---+    +---+    +---+
  • Gradually decrease the number of replicas in the old ReplicaSet: Kubernetes starts scaling down the old ReplicaSet, one instance at a time. For example, it may start by scaling down the old ReplicaSet to three instances and scaling up the new ReplicaSet to one instance. At this point, you have three instances running in the old ReplicaSet and one instance in the new ReplicaSet.
                       +---+    +---+    +---+
Old ReplicaSet (v1)    | 1 |    | 2 |    | 3 |
                       +---+    +---+    +---+

                       +---+    +---+    +---+    +---+
New ReplicaSet (v2)    | 1 |    | 2 |    | 3 |    | 4 |
                       +---+    +---+    +---+    +---+
  • Verify the health of the new ReplicaSet: Kubernetes verifies the health of the new ReplicaSet to ensure that all instances are running correctly. If any issues arise, Kubernetes can stop the deployment and roll back to the previous version.
  • Continue scaling down the old ReplicaSet: Kubernetes continues scaling down the old ReplicaSet and scaling up the new ReplicaSet until all instances in the old ReplicaSet have been replaced by instances in the new ReplicaSet. At this point, you have zero instances running in the old ReplicaSet and four instances in the new ReplicaSet.
                       +---+    +---+    +---+    +---+
Old ReplicaSet (v1)    |   |    | 2 |    | 3 |    | 4 |
                       +---+    +---+    +---+    +---+

                       +---+    +---+    +---+    +---+
New ReplicaSet (v2)    | 1 |    |   |    |   |    |   |
                       +---+    +---+    +---+    +---+
  • Delete the old ReplicaSet: Once the new ReplicaSet has been fully deployed and verified, Kubernetes deletes the old ReplicaSet.
                       +---+    +---+    +---+    +---+
New ReplicaSet (v2)    | 1 |    | 2 |    | 3 |    | 4 |
                       +---+    +---+    +---+    +---+

By using this process, Kubernetes can deploy new versions of an application gradually, one instance at a time, while keeping the existing instances running. This ensures that the application remains available to end-users during the deployment process, without causing any disruption to the user experience.

Benefits of Zero Downtime Deployment

Zero downtime deployment offers several benefits, including:

  • Increased availability: Zero downtime deployment ensures that the application remains available to end-users during the deployment process.
  • Reduced risk: By gradually deploying the new version of the application, Kubernetes reduces the risk of service disruption and enables quick rollback if issues arise.
  • Improved user experience: Zero downtime deployment ensures that end-users can continue to use the application without any interruption, leading to a better user experience.

Conclusion

Zero downtime deployment is a critical feature of Kubernetes that enables the deployment of new versions of an application without causing any disruption to end-users. Kubernetes achieves this through Rolling Updates, a technique that gradually deploys new versions of an application while keeping the existing instances running. By using zero downtime deployment, organizations can increase the availability of their applications, reduce risk, and improve the user experience.

Ramadan Khalifa

Ramadan Khalifa

Berlin