[Monotone-devel] Setting up a "cluster" of monotone servers

[Richard Levitte - VMS Whacker]

Hi,

For a while, I've been thinking about what would be required to have
more than one server respond as if they were one.  One of the goals
with this effort is to be able to have a monotone host name (such as
mtn.lp.se) have more than one A record (in other words, point at more
than one server) and work seemlessly.

The problem is really two-fold:

 1. Keys, permissions and hooks.  These need to be the same on all
    servers, or there will be trouble, either with having users
    suddenly be presented with a different server key, and monotone
    putting up big warnings, or with netsync rights varrying depending
    in which server you happen to hit, or other variations depending
    on the hooks.
    For now, such things can be solved by having a separate set of
    servers for administrative data, with very tight trust settings.
    It's quite possible (I don't know yet) that the future policy
    branches could solve the problem more or less automagically.

 2. Propagation of changes.  The way things look right now,
    propagating changes could easily be done by having all servers
    keep a mirror of the database and sync all changes to all the
    other servers (or in whatever topology you desire).  The trouble
    with this is, of course, latency.  The users may or may not
    experience that the changes they just pushed aren't quite there,
    that they need to push more than once if they're impatient, and so
    on.
    A different solution could be to make it possible for a server to
    initiate a sync with another server, and have that done directly
    after there's been anything happening that changes the contents of
    the database.  This would probably just need a little bit of
    hackery of the netsync code to have an appropriate trigger point
    that starts the netsync, and a hook that returns a list of other
    servers to communicate with.

Thoughts?  Ideas?  Criticism?  Is this at all possible?

Cheers,
Richard

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-- 
Richard Levitte                         address@hidden
                                        http://richard.levitte.org/

"When I became a man I put away childish things, including
 the fear of childishness and the desire to be very grown up."
                                                -- C.S. Lewis