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Re: [Handle-info] how to mirror multiple sites with a single secondary handle server?

Hi Eric,

Your idea is very well thought out and I think it will work. The most important change is obviously the delete_all_handles_stmt because that is called when each of the "fetch" servers begin the mirroring process. I would change delete_all_handles_stmt to a no-op and manually clear the database before starting.

You are right that it is not possible to configure or tune a mirror to pull updates from two separate primary sites. This is because the mirror would have to trust that each of the primary sites didn't update or modify duplicate handles or prefixes. For example, assume primary 1 is responsible for prefix xyz and has a handle xyz/abc. If the administrator of primary 2 were to "home" xyz on primary 2 he could then create his own version of xyz/1 which could overwrite the xyz/1 from primary 1. That administrator could also un-home xyz from primary 2 which would have the effect of un-homing it from the aggregate mirror.

You may have to worry about this case if you have two different and untrusted (by each other) parties with admin rights on primary 1 and primary 2. If both primary servers have the same administrators then it shouldn't be an issue as long as they don't accidentally home or un-home prefixes on the wrong primary.

Thanks,
Sean

On Oct 15, 2007, at 12:21 PM, Eric Auer wrote:

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Hi all,

we would like to mirror several sites with one
single server. To be more exact, we would like
to keep open ports in our firewall at a minimum.

One idea on how to do this, please comment:
We could install 3 servers to mirror 2 sites...
One server would be set to "normal server with
read only access". The other 2 would be set to
"you are a mirror of prefix A" and "you are a
mirror of prefix B". All 3 servers would share
the same SQL database but only the "normal"
server would be accessible from the outside.

The global handle servers would list that one
server as the "actual" mirror for both sites /
prefixed. I assume that mirroring is a "pull"
process so no connections from the outside to
the 2 "fetch data" servers would be needed.
All 3 would use the same public/private keys.

The 2 mirrors would use "tuned" config.dct to
hide the respective other prefixed from each
other or at least avoid interference when they
both write to the same database (which is then
read by the 3rd, read-only server). This would
affect delete_all_handles_stmt and maybe also
scan_nas_stmt/scan_handles_stmt, anything else?

I looked at ReplicationDaemon, at TxnCallback
and at DumpHandlesResponse. It seems that having
a secondary / mirror replicate more than one
server is only supported without trickery if all
primary servers are from the same site? Or is
it possible to "tune" some config / site info
file to tell a mirror to mirror 2 actual sites?
txnsrcsv.bin maybe?

Please let me know if you think this can work,
and if you have further suggestions. It would
be nice if we could avoid having to modify the
source code or having to open many ports when
we mirror many sites.

Thanks :-)

Eric


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