Subject: RE: [midcom] middlebox informs agent?

From: "Cedric Aoun" <[email-masked]>
Date: Mon, 25 Jun 2001 15:33:16 +0100

I agree with the need to keep the session states requested by the agent
after communications are lost for x sec (defined in the agent profile).
The driver for that is that we need to have a fail over mechanism from a
midcom agent to another.

Until now we have never discussed fault tolerance and reliability mechanisms
(as you mentioned below).
In case we do not have a standardized approach of fail over (Melinda, is
this in scope ?) at least have an understanding of what
is the agreed behavior when an agent that didn't reply to a keep-alive
resends later on another keep alive.
In case the middle box accepts to maintain the "connection" (as Suresh calls
it), this allows to use proprietary
Virtual Midcom agents mechanisms (i.e. the Middle box sees only one virtual
agent all the time).

I'm happy to write a section on the subject (either in the FW or in the
requirements draft)
Cedric

-----Original Message-----
From: Scott Brim [mailto:[email-masked]]
Sent: Friday, June 22, 2001 2:46 PM
To: midcom
Subject: Re: [midcom] middlebox informs agent?

On 22 Jun 2001 at 08:32 -0400, Melinda Shore apparently wrote:
> > It wouldn't be controversial except that someone said he really didn't
> > want middleboxes to be required to delete state if an agent disappeared,
> > that pinholes should be left open for some time.
> 
> That "he" would be me.
> 
> That's a sort of a rough paraphrase, Scott.  I'm concerned
> that tearing down state as soon as an agent fails works 
> against fault tolerance.

Sorry about "rough".  OK, can we work toward consensus on requirements?
What specifically is the minimum that is required?  Do you want to
require, say, the agent to state (in the midcom protocol) the minimum
time that installed state should be retained if agent<->middlebox
communication is lost (default to 0)?  Note that this would be after
communication was declared "lost", an interval that hasn't been set
yet.  

I think maybe we should talk about fault tolerance requirements in
general first?

...Scott

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---

From: "Melinda Shore" <[email-masked]>
Date: Mon, 25 Jun 2001 11:34:36 -0400

> From: Cedric Aoun <[email-masked]>
> To: 'Scott Brim' <[email-masked]>; midcom <[email-masked]>
> Sent: Monday, June 25, 2001 10:33 AM
> Subject: RE: [midcom] middlebox informs agent?

> resends later on another keep alive.

Failover is not currently part of the problem space as
we understand it and I'm concerned about scope creep.
At the same time I think we need to take care that the
framework we develop doesn't make failover (either
agents or boxes) unnecessarily difficult.  It seems to 
me that a discussion of failover considerations and
state management/transfer could be useful, but please -
let's avoid introducing new terminology and architecture 
("virtual midcom agents") unless necessary.

Melinda