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+## A use case
+
+Why I needed this plugin: I have two web servers available to me
+for a project. Neither does everything I need, but together they
+do. (This is a bit like the [Amazon S3
+scenario](http://kitenet.net/~joey/blog/entry/running_a_wiki_on_Amazon_S3/).)
+
+Server (1) is a university web server. It provides plentiful space
+and bandwidth, easy authentication for people editing the wiki, and
+a well-known stable URL. The wiki really wants to live here and
+very easily could except that the server doesn't allow arbitrary
+CGIs.
+
+Server (2) is provided by a generous alumnus's paid [[tips/DreamHost]]
+account. Disk and particularly network usage need to be minimized
+because over some threshold it costs him. CGI, etc. are available.
+
+My plan was to host the wiki on server (1) by taking advantage of
+server (2) to store the repository, source checkout, and generated
+pages, to host the repository browser, and to handle ikiwiki's CGI
+operations. In order for this to work, web edits on (2) would need
+to automatically push any changed pages to (1).
+
+As a proof of concept, I added an rsync post-commit hook after
+ikiwiki's usual. It worked, just not for web edits, which is how
+the wiki will be used. So I wrote this plugin to finish the job.
+The wiki now lives on (1), and clicking "edit" just works. --[[schmonz]]
+
+> Just out of interest, why use `rsync` and not `git push`.  i.e. a
+> different setup to solve the same problem would be to run a
+> normal ikiwiki setup on the universities server with its git
+> repository available over ssh (same security setup your using
+> for rsync should work for git over ssh).  On the cgi-capable server,
+> when it would rsync, make it git push.  It would seem that git
+> has enough information that it should be able to be more
+> network efficient.  It also means that corruption at one end
+> wouldn't be propagated to the other end. -- [[Will]]
+
+>> Hey, that's a nice solution. (The site was in svn to begin with,
+>> but it's in git now.) One advantage of my approach in this particular
+>> case: server (1) doesn't have `git` installed, but does have `rsync`,
+>> so (1)'s environment can remain completely untweaked other than the
+>> SSH arrangement. I kind of like that all the sysadmin effort is
+>> contained on one host.
+>>
+>> This plugin is definitely still useful for projects not able to use
+>> a DVCS (of which I've got at least one other), and possibly for
+>> other uses not yet imagined. ;-) --[[schmonz]]
+
+----
+
+Revew: --[[Joey]] 
+
+* I think it should not throw an error if no command is set. Just don't do anything.
+* If the rsync fails, it currently errors out, which will probably also leave
+  the wiki in a broken state, since ikiwiki will not get a chance to save
+  its state. This seems fragile; what if the laptop is offline, or the
+  server is down, etc. Maybe it should just warn if the rsync fails?
+* Is a new hook really needed? The savestate hook runs at a similar time;
+  only issue with it is that it is run even when ikiwiki has not
+  rendered any updated pages. Bah, I think you do need the new hook, how
+  annoying..
+
+> * Depends whether the plugin would be on by default. If yes, then yes.
+>   If the admin has to enable it, I'd think they'd want the error.
+> * Changed the other errors to warnings.
+> * The name might be wrong: there isn't anything rsync-specific about the
+>   plugin, that's just the command I personally need to run. --[[schmonz]]
+
+>> One problem with the error is that it prevents dumping a new setup file with
+>> the plugin enabled, and then editing it to configure. ie:
+
+	joey@gnu:~>ikiwiki -setup .ikiwiki/joeywiki.setup -plugin rsync -dumpsetup new.setup
+	Must specify rsync_command
+
+> rsync seems by far the most likely command, though someone might use something
+> to push via ftp instead. I think calling it rsync is ok. --[[Joey]]