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P.Haul is an extension to CRIU that makes [[live migration]] with CRIU possible.
P.Haul is an extension to CRIU that makes [[live migration]] with CRIU possible. The effort first appeared as [[Py-P.Haul|python script(s)]], but due to high complexity of python code integration, it was switched into Go. Right now the sources are in [https://github.com/checkpoint-restore/go-criu go-criu] repository.
== Description ==
P.Haul library is the pair of Go classes, one to be launched on the source node, the other one on the destination. Users are to import the source into their projects and call function directly. No CLI provided (yet).
=== Configuration ===
Both source and destination should create a <code>PhaulConfig</code> object that configures client and server. The fields are
* <code>Pid</code> -- the pid of the process subtree to live migrate
* <code>Memfd</code> -- file descriptor via which CRIU will send processes' memory contents
* <code>Wdir</code> -- path where CRIU can put intermediate files (images, logs, etc.)
=== Destination ===
Destination process is to call <code>phaul.MakePhaulServer</code> routine, that returns back a handler (and go error). Argument is the <code>PhaulConfig</code> object described above.
=== Source ===
Source is to call <code>phaul.MakePhaulClient</code> routine, it also returns a handler (and go error). Arguments are more complex.
The first is <code>PhaulLocal</code> interface. This one has the single method called <code>DumpCopyRestore</code>. Once p.haul client and server agree, that all preparations (pre-dumps) are done and it's time to call full dump, copy images and call full restore, this method is called. It's up to go-phaul caller to implement this method, as dumping processes is very engine-specific. E.g. OpenVZ, Docker, LXC all have [[CLI|different ways]] of invoking the <code>criu dump</code> operation. In turn, the method accepts
* <code>criu.Criu</code> -- a handler to Criu object from [[go wrappers]] using which client may invoke the dump action
* <code>PhaulConfig</code> object
* <code>last_client_images_path</code> string denoting where the last dump-s are. Needed to configure the [[incremental dumps]] for this final step
Next goes the <code>PhaulRemote</code> interface with a set of methods, that client wants to be called on the server object. It's up to the caller to provide the RPC method for this. E.g. in phaul test the server handler is passed as is as this argument.
The last one is known <code>PhaulConfig</code> object.
After these preparations, the <code>client.Migrate()</code> is to be called.
== Further development plans ==
Right now phaul is an implementation of [[iterative migration]] -- it calls pre-dumps several times, then informs the caller to do final dump-copy-restore steps. It's important to note, that it's up to the caller to copy the generated by last criu call images to the destination node.
To improve the above we want to
* Add [[lazy migration]] support
* Add [[Image_cache/proxy_TODO|automatic images transfer]]
* Add API for FS migration (if necessary)
* Fix [[Py-P.Haul]] to use this library as a core
== Git ==
https://github.com/checkpoint-restore/go-criu
[[Category: Live migration]]
[[Category: New features]]