[CRIU] Process Migration Using Sockets

[Rodrigo Bruno]

On Thu, 30 Jul 2015 18:04:20 +0300
Pavel Emelyanov <xemul at parallels.com> wrote:

> On 07/30/2015 03:42 AM, Rodrigo Bruno wrote:
> > Hi,
> > 
> > I am using CRIU and I extended it to support process live migration using sockets.
> 
> Have you looked at the p.haul stuff we use for the same?

No, I will take a look.

> 
> > The idea is to write to a file descriptor which corresponds to a socket instead of a file.
> 
> You mean write the image files into a socket, don't you?

Yes.

> 
> > The amount of code needed for this modification is very small.
> > 
> > So far my experiments are running smoothly. With this, I do not need a background NFS
> > deployment and performance is much better. The user only needs to specify, in the command
> > line args, that this migration is done using sockets. For now I am using SSH tunnels to
> > redirect and cipher the data between different hosts.
> > 
> > I don't know if this will break any other functionality tough.
> 
> Well, if it's all about image files, then two things to keep in mind.
> 
> First, the contents of the pages.img files can already be sent to
> sockets using page server (http://criu.org/Disk-less_migration).

I only realized that after having my solution working... However, as far as I 
understood, this does not give a full live migration because other img files 
still need to get transferred.

> 
> Second, image objects are read from images in different order from the
> one they were written to. So right now it's not easily possible to
> pipe-line CRIU dump into CRIU restore.

Right. I solved this problem with in-memory file caches (separate process) that hold files' 
contents. On the dump side, the cache receives the files' contents and simply redirects it 
to the restore side cache. The restore side cache holds all files in memory until they are 
requested by the CRIU restore process. This enables multiple files to be sent concurrently,
allowing the restore mechanism to start while the dump mechanism is still running.

> 
> > I am sending this mail to ask you if this contribution is of any interest for the project.
> 
> Of course!
> 
> > If it is, I will be glad to help, providing a patch or whatever you need.
> 
> Sure! The patch is always welcome.

I will wrap up my modifications and submit a patch. =)

> 
> -- Pavel
> 


-- 
Rodrigo Bruno <rbruno at gsd.inesc-id.pt>