If you have ever used tools like Istio, or OpenShift Service Mesh, you may have noticed that they have an ability to modify your Kubernetes deployments automatically injecting “side-cars” into your application definitions. Or perhaps you have come across tools that add certificates to your deployment, or add special environment variables to your definitions. This magic is brought to you by Kubernetes Admission Controllers. There are multiple types of admission controllers, but today we will focus on just one of them, “Mutating Webhooks”. Mutating Webhooks are the specific class of Admission Controller that can inject changes into your Kubernetes definitions.