rsync - May 2011 - [Bug 8188] New: Mechanism for taking an rsync server down for maintenance

https://bugzilla.samba.org/show_bug.cgi?id=8188

           Summary: Mechanism for taking an rsync server down for
                    maintenance
           Product: rsync
           Version: 3.0.8
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P5
         Component: core
        AssignedTo: wayned at samba.org
        ReportedBy: andrew-samba-bugzilla at andrew.net.au
         QAContact: rsync-qa at samba.org


Hi,

I run a mirror, which provides content over rsync, amongst other protocols.

I'm looking for a nicer way to take the rsync component down when I need to
make the mirror unavailable for maintenance. Currently for Apache, I can put up
a server that returns a 503 HTTP response, for FTP, I can use ProFTPd's
ftpshut
command, which puts a file in place that makes ProFTPd return 500 responses for
new connections.

To the best of my reading of the rsync source (start_daemon in clientserver.c),
there doesn't seem to be any such functionality for rsync. I currently have
to
simply stop the rsync daemon, which doesn't convey a useful message to the
user.

I was thinking if for every new connection, the rsync daemon checked for the
existence of a file in /etc (perhaps /etc/rsync.shutdown?) and if this was
present, displayed the contents of the file to the remote user and closed the
connection.
>From my limited understanding of rsync, I presume this would require
extending
the protocol to allow for sending such a message back to the remote client.

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--- Comment #1 from Wayne Davison <wayned at samba.org> 2011-05-31
05:15:51 UTC ---
You could just setup something to echo a one-line message on the socket and
disconnect.  If you're using xinetd, tweak the program to be anything that
outputs a message to stdout.  To replace an rsync daemon, you may want to code
up a C program or use a simple perl script, like this (and run it instead of
the daemon):

#!/usr/bin/perl
use strict;
use warnings;
use Socket;

my $PORT = 873;

local *S;
socket(S, PF_INET, SOCK_STREAM , getprotobyname('tcp'))
    or die "couldn't open socket: $!\n";
setsockopt(S, SOL_SOCKET, SO_REUSEADDR, 1);
bind(S, sockaddr_in($PORT, INADDR_ANY));
listen(S, 25) or die "listen failed: $!\n";

while (1) {
    accept(CON, S);
    print CON "The rsync server is down for maintenance.\n";
    close CON;
}

Any connecting rsync will then output this:


rsync: server sent "The rsync server is down for maintenance." rather
than
greeting

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--- Comment #2 from Andrew Pollock <andrew-samba-bugzilla at
andrew.net.au> 2011-06-02 04:34:54 UTC ---
Created attachment 6513
  --> https://bugzilla.samba.org/attachment.cgi?id=6513
Proof of concept patch

This is purely a proof of concept patch and not production-grade.

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--- Comment #3 from Andrew Pollock <andrew-samba-bugzilla at
andrew.net.au> 2011-06-02 04:36:12 UTC ---
(In reply to comment #1)

That's very cute, but not quite what I had in mind.

I just attached a proof of concept patch that I surprised myself by being able
to hack together the other night.

The real thing probably needs to be configurable, and it'd probably be
better
to get the message from the contents of the file (if there was any).

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--- Comment #4 from Brian K. White <brian at aljex.com> 2011-06-02
21:47:32 UTC ---
(In reply to comment #3)
> (In reply to comment #1)
> 
> That's very cute, but not quite what I had in mind.
> 
> I just attached a proof of concept patch that I surprised myself by being
able
> to hack together the other night.
> 
> The real thing probably needs to be configurable, and it'd probably be
better
> to get the message from the contents of the file (if there was any).
Someone else emailed me an untested idea to just use exclude file and
place/remove/edit the exclude file to toggle the access.

That doesn't provide the truly graceful/informative response code or
message,
but:
* toggles the access
* avoids downing the service even momentarily
* potentially avoids requiring a host admin to even do anything, since a user
may have permission to place/remove the exclude file
* it's at least distinct from failed to connect
* uses already existing features
* does not require any, let alone two different, wrapper layers in the form of
the perl (or other) wrapper script and (x)inetd to run it.

I haven't finished playing around with that to see just how close that can
come
to the desired fully graceful process but I felt it should be mentioned as
another workaround option.

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bkw

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--- Comment #5 from Andrew Pollock <andrew-samba-bugzilla at
andrew.net.au> 2011-06-03 03:56:14 UTC ---
(In reply to comment #4)
> (In reply to comment #3)
> > (In reply to comment #1)
> > 
> > That's very cute, but not quite what I had in mind.
> > 
> > I just attached a proof of concept patch that I surprised myself by
being able
> > to hack together the other night.
> > 
> > The real thing probably needs to be configurable, and it'd
probably be better
> > to get the message from the contents of the file (if there was any).
> 
> Someone else emailed me an untested idea to just use exclude file and
> place/remove/edit the exclude file to toggle the access.
> 
> That doesn't provide the truly graceful/informative response code or
message,
> but:
> * toggles the access
> * avoids downing the service even momentarily
> * potentially avoids requiring a host admin to even do anything, since a
user
> may have permission to place/remove the exclude file
> * it's at least distinct from failed to connect
> * uses already existing features
> * does not require any, let alone two different, wrapper layers in the form
of
> the perl (or other) wrapper script and (x)inetd to run it.
> 
> I haven't finished playing around with that to see just how close that
can come
> to the desired fully graceful process but I felt it should be mentioned as
> another workaround option.
The same could be said for my "patch". If the file that is checked is
configurable, and the contents of the file are used to obtain the message, then
it also

* toggles the access
* avoids downing the service even momentarily
* can potentially avoid the host admin having to do anything if the file is in
a user-writable location (I personally don't consider this to be a desirable
feature)
* doesn't require wrappers

I'm prepared to continue futzing around with my patch if it has merit,
I'm just
not a very competent C programmer.

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Wayne Davison <wayned at samba.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
            Version|3.0.8                       |3.1.0
         Resolution|                            |FIXED

--- Comment #6 from Wayne Davison <wayned at samba.org> 2011-06-04
19:00:14 UTC ---
I've committed a change to 3.1.0dev git that allows a pre-xfer exec script
to
send an error message to go with its non-zero exit status.  This will allow
someone to tweak their rsyncd.conf file to add a global option like the
following (assuming that they don't override pre-xfer exec elsewhere):

pre-xfer exec = /usr/local/bin/output-rsyncd-downtime-message

That script may output a message to stdout and then exit with a non-zero
status.

You could also choose to leave the pre-xfer exec configured, and make the
script do your file-check:

#!/bin/sh
if [ -f /rsyncd.downtime ]; then
    cat /rsyncd.downtime
    exit 1
fi

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--- Comment #7 from Andrew Pollock <andrew-samba-bugzilla at
andrew.net.au> 2011-06-05 16:24:01 UTC ---
(In reply to comment #6)
> I've committed a change to 3.1.0dev git that allows a pre-xfer exec
script to
> send an error message to go with its non-zero exit status.  This will allow
> someone to tweak their rsyncd.conf file to add a global option like the
> following (assuming that they don't override pre-xfer exec elsewhere):
> 
> pre-xfer exec = /usr/local/bin/output-rsyncd-downtime-message
> 
> That script may output a message to stdout and then exit with a non-zero
> status.
> 
> You could also choose to leave the pre-xfer exec configured, and make the
> script do your file-check:
> 
> #!/bin/sh
> if [ -f /rsyncd.downtime ]; then
>     cat /rsyncd.downtime
>     exit 1
> fi
Sweet! Thanks!

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--- Comment #8 from Brian K. White <brian at aljex.com> 2011-06-06
15:36:52 UTC ---
(In reply to comment #6)
> I've committed a change to 3.1.0dev git that allows a pre-xfer exec
script to
> send an error message to go with its non-zero exit status.  This will allow
> someone to tweak their rsyncd.conf file to add a global option like the
> following (assuming that they don't override pre-xfer exec elsewhere):
> 
> pre-xfer exec = /usr/local/bin/output-rsyncd-downtime-message
> 
> That script may output a message to stdout and then exit with a non-zero
> status.
> 
> You could also choose to leave the pre-xfer exec configured, and make the
> script do your file-check:
> 
> #!/bin/sh
> if [ -f /rsyncd.downtime ]; then
>     cat /rsyncd.downtime
>     exit 1
> fi
Sometimes, you ask for an inch, they give you a mile. ;)

-- 
bkw

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