Re: Process Migration on Linux - Impossible?

David Schwartz (djls@gate.net)
Wed, 01 Oct 1997 12:48:46 -0400

At 11:05 AM 10/1/97 -0500, Tall cool one wrote:
>Victor Yodaiken <yodaiken@chelm.cs.nmt.edu> writes:
>> On Tue, Sep 30, 1997 at 10:06:25PM -0500, Tall cool one wrote:
>> > Personally, I don't have a real need for process migration, but I'd
like
>> > to see it because of what process migration would allow. The ability of
>>
>> So you want fault tolerance, not process migration. Don't confuse the
>> technique with the result.
>
> That's an odd thing to say, isn't it? Re-read my first sentence again,
>carefully this time. If one can throw a process on another machine at will,
>it becomes trivial to checkpoint, yes? Fault tolerance for free.

Nope. Not so. You can't migrate a TCP/IP connection between machines even
if you migrate the process that owns it. Fault tolerance and process
migration are 100% separate issues.

> Okay, I'd like to see proccess migration, process checkpointing, and fault
>tolerance (especially fault tolerance). Whatever makes you happy.
>
> Typically I wouldn't need to migrate network applications, although it
>could conceivably be possible with some sort of proxying. Not that I'd want
>to implement it. =) Or perhaps the machines share the same IP's but have an
>running agreement on what ports on which machines the IP's go to. Probably
>could be done with local firewall rules. Need a userland daemon to keep the
>"port-map" in sync though.

Network I/O is not the only problem. File I/O is just as important and
just as serious.

DS