Kubernetes
Kubernetes, also known as K8s, is an open-source system for automating deployment, scaling, and management of containerized applications. Unlike many systems before it, Kubernetes is fully multi-cloud and truly planet-scale. At the time of this writing, there is a theoretical limit of a single cluster having 25 million nodes, with each node having thousands of CPUs and millions of GPUs. In practice, clusters tend to be much smaller than that, but they also tend to be very dynamic and scale as needed.
It uses a YAML based Declarative IaC syntax to orchestrate Containers. While there are alternatives like Nomad, Docker Swarm, and DCOS, realistically, they each have limitations that Kubernetes does not, making it likely that you will decide to (or be forced to) migrate.
If you want to avoid cloud vendor lock-in or operate in a Hybrid Cloud environment, Kubernetes is essential.