In practice, containers are process groups with access restrictions.
In theory, though, containers are simply an optimization of virtual machines, and are best understood that way. If you can use virtual machines to solve a problem--and your virtual machines are all generally based on a recent Linux--then you can achieve the same thing, using far fewer resources, by using containers.
In theory, though, containers are simply an optimization of virtual machines, and are best understood that way. If you can use virtual machines to solve a problem--and your virtual machines are all generally based on a recent Linux--then you can achieve the same thing, using far fewer resources, by using containers.