rkt was needed to push a number of ideas forward in the ecosystem at the time (4 years ago, 2014) and part of its legacy is the creation of technologies that pr

rkt was needed to push a number of ideas forward in the ecosystem at the time (4 years ago, 2014) and part of its legacy is the creation of technologies that provided plugin interfaces for the container ecosystem. The Container Networking Interface was directly created by the work in rkt and continues on today inside of Kubernetes and the CNCF. This work made it possible for an ecosystem of networking solutions to exist that could take advantage of everything Linux has to offer. The creation of the Kubernetes Container Runtime Interface (CRI) was also spawned, in part, by the existence of rkt and the need to consider container runtimes for use with Kubernetes. It was a long hard engineering effort but I think the separation that CRI forced the kubelet to go through and the competition of various runtimes is good for the ecosystem and the resilience of the Kubernetes project. It is very unlikely that rkt will be part of the Kubernetes ecosystem at this point with the existence of containerd, and CRI-O as Kube CRI solutions on Linux. And there were missed opportunities on a variety of fronts along the way. But, rkt continues to be used by many organizations for other niche use cases of containers. And the shifts that rkt caused above were positive improvements for the Kubernetes ecosystem.