==========
XL Migrate
==========

:Author: Zhigang Wang
:Contact: zhigang.x.wang@xxxxxxxxxx
:Date: 2013-03-08

Current Status
==============

* xl migrate leverages ssh/sshd.

* In order to migrate a VM without user interactive, we have to configure ssh
  keys for all Servers in a pool. Key management brings complexity.

* In certain cases, customers need non-ssl migrate, which greatly improves the
  migration speed. There's no way to do it with ssh.

* Current xl migrate command is not intuitive, especially the `-s` option::

      # xl migrate
      Usage: xl [-v] migrate [options] <Domain> <host>
      
      Save a domain state to restore later.
      
      Options:
      
      -h              Print this help.
      -C <config>     Send <config> instead of config file from creation.
      -s <sshcommand> Use <sshcommand> instead of ssh.  String will be passed
                      to sh. If empty, run <host> instead of ssh <host> xl
                      migrate-receive [-d -e]
      -e              Do not wait in the background (on <host>) for the death
                      of the domain.

  It's a little hard to adapt other tools as transport.

* We have differnt implementation for `xl save/restore` and `xl migrate/migrate-receive`. Can we merge them?


Proposal
========

* Implement dedicated daemons for ssl and non-ssl migration receive (`socat <http://www.dest-unreach.org/socat/>`_ can be used).

  Example patch for dedicated migrate receive daemon: xen-xl-migrate-socat.patch

  `socat` will call `xl restore` instead of `xl migrate-receive` after the following change.

* Merge `xl migrate/migrate-receive` to `xl save/restore`:

  - To save a VM::

      # xl save [-c] <domain> -f vm.chk

    Or::

      # xl save [-c] <domain> >vm.chk

  - To restore a VM::

      # xl restore -f vm.chk

    Or::

      # cat vm.chk | xl restore

  - To migrate a VM using ssh/sshd::

      # xl save -c <domain> | ssh root@<remote-host> xl restore

    We can implement a wrapper to make `xl migrate <domain> <remote-host>` to call the above command. 

  - To migrate a VM using dedicated migrate receive daemon::

      # xl save -c <domain> | socat - TCP:<remote-host>:8004"

    Or with SSL::

      # xl save -c <domain> | socat - OPENSSL:<remote-host>:8005,verify=0

  - Localhost migration::

      # xl save <domain> | xl restrore

  - Localhost live migration::

      # xl save -c <domain> | xl restrore

  Patch: I don't have the capability and time to implement it yet.