[Opensim-users] Sim Version Filtering (re: Mantis #0002361: adding simulator release control at grid level to avoid out of date simulator registration )

[James Stallings II]

Greetings Devs :)

Sacha Magne had asked me to annotate this issue in the Mantis, perhaps
unawares that it was an issue rather close to my heart, as I have been
asking for something like this for some time.

As my thinking on this somewhat exceeds the scope of a note to the mantis, I
decided to make my post here instead.

The short take: I think this is a feature very much in need of
implementation, generally speaking - I think it impacts region (and
therefore grid) stability in a sufficiently significant manner that it
should take on an increased level of prioritization.

The long view: Simply put, refusing to register an out of date revision of
the region is not sufficient to the cause. Additionally, there is the
(valid) conern about SVN revision numbers being used to track the
'fingerprint' of a simulator that is being connected.

First, I'll address the issue of SVN revision number as a fingerprint:

While it may not be the most desireable means of identifying the region for
these purposes, it is the one that has the ideal level of granularity - as
quickly as the project moves, and as dramatic as changes in operations
sometimes are, the release number is simply not sufficient to the cause as
we currently stamp releases. So, in order to make this feature deliver
acording to the need, we either must use the SVN revision number, or come up
with some other methodology for identifying the age of the region in  terms
of its functional age. The obvious thing to use is the revision number, as
it tracks the level of change at precisely the right granularity. The
question becomes then one of pinning the revision down in the runtime
environment. There are already provisions in place for this to happen, and
if the software is built to accomodate it, the revision will be available at
run-time - it may be sufficient to say that from the point of the
introduction of this feature, any region not built such that it identifies
itself by revision number is disallowed from participation (provided, of
course, that this feature is enabled in the approriate config file).

Finally, I'll address the insufficiency of this approach as a solution:

Denying registration of a new region for these purposes is good - but it's
not the full solution to the problem. First, I suppose I need to point out
the obvious in order to lay the groundwork for my assertion: a running
simulator connected to a grid is not 'connected' in any meaningfull sense;
rather, it is 'registered'. Registration means that the simulator has a)
permission to use the grid services provided, and b) sufficient information
on file in the grid backstore to facillitate the delivery of grid services
to the simulator. This is significant because, for instance, one may upgrade
a grid in the presence of many running and 'connected' simulators, and
provided there is not sufficient change in the protocols, the simulator will
never be the wiser for it.

Consequently, we need not only a way to refuse 'simulator X' registration on
the grounds of it's revision relative to the grid, but also a mechanism for
refusing service based on the relative simulator revision, and a mechanism
for arbitrarily deregistering a simulator altogether. This will effectively
temporarily or permanantly remove a region from the grid, given sufficient
differences in the revision in the one instance, or operator intervention in
the other. This will effectively implement the philosophy Sacha is
attempting to express with his patch :)

I think it is fairly important that we do this; not just because I am
constantly beset on some border by misconfigured regions, but because it
will help to ensure a more 'statistically controlled' environment from a
testing and debugging standpoint; in other words, we can count on regions to
behave in particular ways when we have some control over what revision is
talking with the grid or with other simulators.

I apologize for being so long winded - I hope you have made it through my
post without getting a headache.

Cheers
James


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