Add proof of concept for pull mechanism #6270
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Added a small proof of concept for a pull mechanism implementation. Works fine for simple test cases, but probably needs many improvements to be useful for more complex usage scenarios.
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interesting idea / PR, thanks for this!
as you said it likely needs more work (code as well as docs).
i can help with this, but considering i maybe won't use this and also that noone else made such a PR (IIRC), i guess you would be needed to do the main work.
whether this can be merged depends a bit on how big it gets in the end (I do not want to make the client/server stuff even more complex than it already is, esp. considering that debugging this is hard and a lot of work).
is this "PoC" practically working?
| @@ -4630,6 +4632,9 @@ def define_borg_mount(parser): | |||
| 'When a new repository is initialized, sets the storage quota on the new ' | |||
| 'repository as well. Default: no quota.') | |||
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| subparser.add_argument('--pull-command', metavar='cmd', dest='pull_command', | |||
| help='command to use for pulling from a borg server started in serve:// mode') | |||
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isn't that confusing?
the source of the data is always where the borg client runs and the destination of the data is where borg serve(r) runs (which feeds the data into the repo).
so the data is either pushed from client to server (what we ever did) or pulled from the client to the server.
but we never are "pulling from a borg server" (I guess you meant that the pulling action is executed on the server, but that is not really clear).
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same applies for the PR text (which in the end needs to be refactored and moved into the documentation).
isn't is simpler/less confusing if we just define borg server == where "borg serve" runs (and usually where repo is located) and borg client == where the to-be-backed-up files are located == where the stuff is encrypted/compressed/etc.?
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the PR top-post text is confusing the hell out of me. is it just me? please re-read / re-write.
| os.set_blocking(stdout_fd, True) | ||
| os.set_blocking(stderr_fd, True) | ||
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| if self.pull_command: |
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can you please reverse this, so that what we had in the past (push) is in the if-block and the new stuff is generally in the else-block?
| os.set_blocking(self.stdin_fd, False) | ||
| os.set_blocking(self.stdout_fd, False) | ||
| os.set_blocking(self.stderr_fd, False) | ||
| if serve: |
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also reverse blocks please.
Codecov Report
@@ Coverage Diff @@
## master #6270 +/- ##
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- Coverage 83.26% 83.17% -0.10%
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Files 38 38
Lines 10392 10406 +14
Branches 2041 2043 +2
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+ Hits 8653 8655 +2
- Misses 1230 1242 +12
Partials 509 509
Continue to review full report at Codecov.
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BTW, considering there is quite some interest in a safe and good working "pull mode" and that it is quite some work making this work, we could have a bounty ($$$) for this. Maybe there could be a part for related research / experiments independent of whether the stuff gets merged in the end. |
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@qtc-de did you see my feedback? |
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Yes, I saw it. Unfortunately I currently don't have the time to implement this. Maybe at the end of the year, but not sure. However, I'm also fine if someone else picks up the idea and starts working on it 🙂 |
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I'd ❤️ to see this implemented 👍 Just to get this straight, the only reason why this is just a PoC (i.e. non-mergeable) is that it lacks support for more than plain Why don't we simply create a "universal communication interface" - i.e. a socket - and leave things up to the user to use this socket? One can then utilize SSH's port forwarding to get the wished pull mechanism. Since [user@host opt]$ borg init --encryption repokey backup
Enter new passphrase: example123
[user@host opt]$ borg list /opt/backup/
Enter passphrase for key /opt/backup: example123
[user@host opt]$ borg serve --socket /opt/backup/borg.sock
… … … blocking until terminated … … …[user@host opt]$ ssh -i ./id_rsa -R /run/borg.sock:/opt/backup/borg.sock root@172.17.0.2 borg create socket:///run/borg.sock::'{now}' /etc /opt
Enter passphrase for key /run/borg.sock: example123
[user@host opt]$ borg list /opt/backup/
Enter passphrase for key /opt/backup: example123
2022-02-10T22:07:54 Thu, 2022-02-10 23:07:54 [1713f6df6648055c3de2574e014ec45c91c8bf464cca4b27e72ef095d6820a94]Note: If one adds [user@host opt]$ ssh -i ./id_rsa -R /run/borg.sock:/opt/backup/borg.sock root@172.17.0.2
Enter passphrase for key /run/borg.sock: example123
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Hi there 👋
first of all: This is not a real pull request. It is basically a proof of concept for an operation that I would love to see being implemented, but that is far to complex to implement it by myself. The operation itself is quite simple (as demonstrated by this PR), however, it probably requires changes in many other locations of this project.
So what is this PR about? It implements a simple proof of concept for a Pull Operation. Currently, the recommended way to perform a backup in pull mode is using sshfs, which has several drawbacks as outlined in the documentation. After looking into how push backups are implemented, I did not understand why pull backups are not implemented in the same way. Since the remote backup mechanism simply utilizes stdin and stdout of an ssh connection, it is basically invertible and it is possible to create a pull mechanism in the same way.
When applying the patch contained within this PR, the
borg createcommand allows a new protocol type to useserve://<repo>. When using this protocol type, borg behaves basically the same as during a push operation, but outputs all RPC commands to stdout and obtains input from stdin. Therefore,borg createwith theserve://protocol is expected to run on the server side where the update is pulled from.On the other side, on the local backup server, the
borg serveoperation got a new option--pull-command. This option expects the command to use for a connection to the serving borg server in pull mode.And that's basically everything. So let's look at a short demonstration: On the server side we write the following in our authorized-keys file:
On the client side we create a new repo and attempt a backup in pull mode:
This example demonstrates that everything works like expected. That being said, this was obviously an easy example and there are many edge cases. One example is e.g. when unencrypted repositories are used. In this case
borg createasks for user confirmation, which obviously breaks the pull backup. Furthermore, the whole approach is not very flexible. It would be nice if clients could specify additional parameters that are used during the backup on the server side.So like I said, there is a lot of work to be done. However, this PR demonstrates that creating updates in pull mode is basically possible by recycling already existing mechanisms. Feel free to close this PR and to use the code snippets from it during your development process. I thought is would be easier to monitor my changes than creating an issue, but I'm aware that this PR should not be merged in it's current state.