Nix vs Docker

Nix is a purely functional package management system. This means that the act of building a package does not have side effects, such as destructively updating or deleting files that may be used by other packages.

Nix allows the creation of project-specific shell and build environments which are isolated from the rest of the system. These environments are defined declaratively to ensure reproducibility.

Because of the functional approach it takes, Nix makes it easy for systems to use multiple versions of the same package simultaneously, and ensure that updating or removing a package can't break other packages.

No more of the traditional: "it works on my machine". When it says reproducible, this is the real deal.

Docker creates a single object, containing an application with its dependencies, that can be moved between any docker-enabled machines, guaranteeing the same environment for application execution.

Docker tracks changes in systems. It allows for commits and rollbacks and for quick deployment due to having to deploy only the updated code.

Docker essentially allows creating boilerplate systems (a LAMP stack, for example) that can be used as a starting point on multiple projects. And you can find multiple such containers already created by people in their public registry.

Allows automatically assembling a container from its source code.

Docker allows easily pushing and pulling containers to and from their public index.docker.io registry. Additionally, dotCloud maintains a list of official repositories of the more popular containers.

You can set up Docker within an already virtualized environment such as a virtual machine. This allows you to run Docker on Mac and Windows, among other use-cases.

Docker can be used with OpenVZ, systemd-nspawn, libvirt-lxc, libvirt-sandbox, qemu/kvm, BSD Jails, Solaris Zones, and chroot.