  Container technologies, like Docker, are becoming increasingly popular.
Containers provide exceptional developer experience because containers offer
lightweight isolation and ease of software distribution. Containers are also
widely used in production environments, where a different set of challenges
arise such as security, networking, service discovery and load balancing.
Container cluster management tools, such as Kubernetes, attempt to solve these
problems by introducing a new control layer with the container as the unit of
deployment. However, adding a new control layer is an extra configuration step
and an additional potential source of runtime errors. The virtual machine
technology offered by cloud providers is more mature and proven in terms of
security, networking, service discovery and load balancing. However, virtual
machines are heavier than containers for local development, are less flexible
for resource allocation, and suffer longer boot times. This paper presents an
alternative to containers that enjoy the best features of both approaches: (1)
the use of mature, proven cloud vendor technology; (2) no need for a new
control layer; and (3) as lightweight as containers. Our solution is i2kit, a
deployment tool based on the immutable infrastructure pattern, where the
virtual machine is the unit of deployment. The i2kit tool accepts a simplified
format of Kubernetes Deployment Manifests in order to reuse Kubernetes' most
successful principles, but it creates a lightweight virtual machine for each
Pod using Linuxkit. Linuxkit alleviates the drawback in size that using virtual
machines would otherwise entail, because the footprint of Linuxkit is
approximately 60MB. Finally, the attack surface of the system is reduced since
Linuxkit only installs the minimum set of OS dependencies to run containers,
and different Pods are isolated by hypervisor technology.
