[Spread-users] Communicating between 130 hosts with Spread

[Jim Hague]

Hi John,

I somehow managed to miss your reply - just found it in the list archives.

On Wed Jul 31, John Schultz wrote:
> A spread deployment can usually handle thousands of clients served by at
> most a few tens of daemons.  We typically do not recommend casual users to
> try running Spread deployments bigger than say 40 daemons or so (especially
> across a WAN) and even that size is usually massive overkill for most
> applications.

OK, thanks. I was suspecting that this was the case, but this wasn't 
completely clear from my reading of the user guide.

> The primary advantage of running a daemon on the same machine as client
> applications is that the client-daemon communication doesn't go over the
> network.  This means less traffic on your network and also that certain
> kinds of faults can't really happen (e.g. - network partitions, only one
> side of the connection abruptly fails, etc.) and/or are more easily and
> quickly detected.  Furthermore, on *nix systems you can use IPC rather than
> TCP, which is less intensive on the CPU.  Also, the more daemons you have
> then the more distributed the load of the system (i.e. - handling clients)
> can be across all the daemons.

I should have noted that we're deployed on AIX and Linux/x86 exclusively. I'm 
sure you have a bucketload of experience with Linux. Out of curiosity, do you 
know of any AIX users? Just so I can make a few more reassuring noises at 
management should they choose to take an interest. :-)

> Which structure of deployment is best for you depends on particulars such as
> what kind of throughput in Mb/s and msgs/s you expect to go through the
> system in total, how much redundancy you want in each site, what do you
> want to happen if the WAN partitions, etc.

I think our applications could be described as 'undemanding'. Those we have in 
mind for Spread right now have throughputs of a few kb/s and maybe 10 msg/s. 

> As a rough guess at what might work for you, assuming your application isn't
> all that demanding, I'd guess that one Spread segment for your central
> office and one for each remote site each containing a few (e.g. - 3)
> daemons would suffice.  Clients would (remotely) connect to one of the
> daemons at their local site, potentially failing over within a site if a
> daemon is down or even to another site if all the daemons in its site are
> down.

That's exactly what I was envisaging. I presume that client failover between 
daemons is something we'd need to handle ourselves. If we do lose 
communication with a daemon, or a daemon goes down, how quickly will we find 
out about it?

> There's little need to get too fancy with depending on the network
> structure, VLANs, multicast, etc.  Just run each spread segment in a LAN
> and so long as all the daemons in the system can talk point-to-point with
> all the other daemons in the system and your clients can reach their
> daemons then that would likely work for you.

Good. I'm pretty sure that all the daemons will be able to communicate 
directly with each other, so we should be able to keep it simple.

> If you are having lots of trouble or have more demanding needs than I
> guessed, then my company, Spread Concepts LLC, offers support contracts and
> would be happy to work with you on your particular problems.

At this stage we're investigating the technology. Should we look like moving 
to deployment, I'm sure we'll be wanting your commercial services :-)

> PS - Does ATC stand for Air Traffic Control?

Yes, it does. We are active in that business, mainly in the Czech Republic.
-- 
Jim Hague
jim.hague at laicatc.com              Never trust a computer you can't lift.
LAIC AG                            +44 1865 980647    Mob +44 7941 697732

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