Istio is a service mesh designed to help manage microservices monitoring, authentication, security, load balancing, and more in a Kubernetes environment. It provides advanced features for managing internal traffic management, routing, and security capabilities for microservices-based applications. Istio can be used to enforce strong authentication and authorization requirements between microservices, provide application performance and traffic management, and offer granular visibility into the health of each microservice. However, it also has some downsides, such as increased complexity, potential performance reduction, resource consumption, and a learning curve. The future of service meshes may involve less Istio sidecars and more eBPF, which offers similar benefits with better efficiency. Istio is not part of OpenShift by default, but Red Hat's version provides unique integrations with OpenShift. It replaces kube-proxy in some respects but doesn't automatically delete it. NGINX can be used as an internal ingress controller for basic setups, but Istio is better suited for complex use cases. Kubernetes and Istio are both used to manage container-based applications, with Kubernetes providing deployment management and Istio focusing on networking and security management.