No matter the fancy name used here, both are solutions to a specific problem: A better segregation solution than classic Unix chroot. Operating system-level virtualization, containers, zones, or even "chroot with steroids" are names or commercial titles that define the same concept of userspace separation, but with different features.
Chroot was introduced on 18 March 1982, months before the release of 4.2 BSD, as a tool to test its installation and build system, but today it still has its flaws. Since the first objective of chroot was only to provide a newroot path, other aspects of system that needed to be isolated or controlled got uncovered (network, process view, I/O throughput). This is where the first containers (User-level virtualization) appeared.
Both technologies (FreeBSD Jails and LXC) make use of userspace isolation to provide another layer of security. This compartmentalization will ensure that a determined process will communicate only with other processes in the same container on the same host, and if using any network resource to achieve "outside world" communication, all will be forwarded to the assigned interface/channel that this container has.
- Considered stable technology, since it is a feature inside FreeBSD since 4.0;
- It takes the best of ZFS filesystem at the point where you could clone jails and create jail templates to easily deploy more jails. Some more ZFS madness;
- Well documented, and evolving;
- Hierarchical Jails allow you to create jails inside a jail (we need to go deeper!). Combine with
allow.mount.zfs to achieve more power, and other variables like
children.max do define max children jails.
- rctl(8) will handle resource limits of jails (memory, CPU, disk, ...);
- FreeBSD jails handle Linux userspace;
- Network isolation with
vnet, allowing each jail to have its own network stack, interfaces, addressing and routing tables;
nullfs to help linking folders to ones that are located on the real server to inside a jail;
- ezjail utility to help mass deployments and management of jails;
- Lots of kernel tunables (
security.jail.allow.* parameters will limit the actions of the root user of that jail.
- Maybe, FreeBSD jails will extend some of the VPS project features like live migration in a near future.
- Alternatives: FreeBSD VPS project
Linux Containers (LXC):
- New "in kernel" technology but being endorsed by big ones;
- Unprivileged containers starting from LXC 1.0, makes a big step into security inside containers;
- UID and GID mapping inside containers;
- Kernel namespaces, to make separation of IPC, mount, pid, network and users. These namespaces can be handled in a detached way, where a process that uses a different network namespace will not necessarily be isolated on other aspects like storage;
- Control Groups (cgroups) to manage resources and grouping them;
- Extensible API like Docker. Note here that Docker is a "wrap" of LXC using namespaces, cgroups and containers creating "per app"/"per software" isolation. Key differences here.
- Effort on integrating Docker with SELinux and reducing capabilities inside a container to make it more secure - Docker and SELinux, Dan Walsh
- Live migration functionality being developed. It’s really hard to say when it will be ready for production use, since docker/lxc will have to deal with userspace process pause, snapshot, migrate and consolidate - ref1, ref2
- Alternatives: OpenVZ, Docker
Neither technology is a security panacea, but both are pretty good ways to isolate an environment that doesn’t require Full Virtualization due to mixed operating systems infrastructure. Security will come after a lot of documentation reading and implementation of kernel tunables, MAC and isolations that those OS-Level virt offer to you.