VM vs Container Xen, KVM, VMware, etc. Hardware emulation / paravirtualization Can run different OSs on the same box Dozens of instances OS sprawl problem Lower performance Chroot on steroids Single OS per box Hundred of instances Dynamic resource management, best scalability Trivial performance overhead

OpenVZ vs. Xen comparison by HP labs “For all the configurations and workloads we have tested, Xen incurs higher virtualization overhead than OpenVZ does.” “For all the cases tested, the virtualization overhead observed in OpenVZ is low, and can be neglected in many scenarios.” “The two nodes running Xen become overloaded when hosting four instances of RUBiS, whereas those using OpenVZ can host at least six without being overloaded.” From

3 Usage Scenarios Server Consolidation High Availability Hosting Dynamic Load Balancing Development and Testing Security Isolation Educational

New Stuff RHEL6 kernel port VSwap: easy management, RSS reclamation Containers CPU binding (cpumask) PCI device delegation NFS mounts migration Journaled quota ext4 safe writeback

Future directions Mainstream kernel integration Container in a file a.k.a. PLOOP  Come to see our talk! CRIU: checkpoint/restore in userspace Caching de-duplicating FS (pfscache)

Mainstream kernel integration OpenVZ project pioneers container technology  Developing new container technology since Features then ported from OpenVZ to upstream Linux “containers”. Already upstream (in Linux containers):  IPC namespace, utsname() virtualization, PID namespace, user namespace, cgroups (control groups), Memory controllers (RSS, page cache), Network namespace...  Collaborative community effort: IBM, Google, SGI, Parallels, and many others. It's still ongoing  In progress: NFS virtualization, network buffer accounting, Checkpoint/restart in userspace  TODO: Kernel memory accounting,...

CT #1 Migration at a Glance Physical Server #1Physical Server #2 CT Private Data CT Memory CT#1 Container's file system transfer Save full container's state to a file Container is running on Server #1 Full State Dump Restart container on Server #2 CT #1 CT Memory CT Private Data

To sum it up Containers scale as well as Linux does  Benefit from all Linux performance improvements  Native I/O speed, best possible performance  The more memory/CPUs the merrier Platform-independent  as long as Linux supports it, we support it  arm/mips/ppc no problem. Plays well with others (Xen, KVM, VMware)  VM and container technologies are orthogonal  run containers and VMs side by side