git-annex/doc/design/assistant/cloud.mdwn

The [[syncing]] design assumes the network is connected. But it's often
not in these pre-IPV6 days, so the cloud needs to be used to bridge between
LANS.

## The cloud notification problem (**done**)

Alice and Bob have repos, and there is a cloud remote they both share.
Alice adds a file; the assistant transfers it to the cloud remote.
How does Bob find out about it?

There are two parts to this problem. Bob needs to find out that there's
been a change to Alice's git repo. Then he needs to pull from Alice's git repo,
or some other repo in the cloud she pushed to. Once both steps are done,
the assistant will transfer the file from the cloud to Bob.

* dvcs-autosync uses xmppp; all repos need to have the same xmpp account
  configured, and send self-messages. An alternative would be to have
  different accounts that join a channel or message each other. Still needs
  account configuration.
* irc could be used. With a default irc network, and an agreed-upon channel,
  no configuration should be needed. IRC might be harder to get through
  some firewalls, and is prone to netsplits, etc. IRC networks have reasons
  to be wary of bots using them. Only basic notifications could be done over
  irc, as it has little security.
* When there's a ssh server involved, code could be run on it to notify
  logged-in clients. But this is not a general solution to this problem.
* pubsubhubbub does not seem like an option; its hubs want to pull down
  a feed over http.

See [[xmpp]] for design of git-annex's use of xmpp for push notifications.

## storing git repos in the cloud **done for XMPP**

Of course, one option is to just use github etc to store the git repo.

Two things can store git repos in Amazon S3:
* <http://gabrito.com/post/storing-git-repositories-in-amazon-s3-for-high-availability>
* <http://wiki.cs.pdx.edu/oss2009/index/projects/gits3.html>

Another option is to not store the git repo in the cloud, but push/pull
peer-to-peer. When peers cannot directly talk to one-another, this could be
bounced through something like XMPP. This is **done** for [[xmpp]]!

Another option: Use <https://github.com/blake2-ppc/git-remote-gcrypt> to store
git repo encrypted on cloud storage.