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README

Archvsync
=========

This is the central repository for the Debian mirror scripts. The scripts
in this repository are written for the purposes of maintaining a Debian
archive mirror (and shortly, a Debian bug mirror), but they should be
easily generalizable.


Currently the following scripts are available:

* ftpsync - Used to sync an archive using rsync
* runmirrors - Used to notify leaf nodes of available updates
* dircombine - Internal script to manage the mirror user's $HOME
on debian.org machines
* typicalsync - Generates a typical Debian mirror
* udh - We are lazy, just a shorthand to avoid typing the
commands, ignore... :)

Usage
=====
For impatient people, short usage instruction:

- Create a dedicated user for the whole mirror.
- Create a seperate directory for the mirror, writeable by the new user.
- Place the ftpsync script in the mirror user's $HOME/bin (or just $HOME)
- Place the ftpsync.conf.sample into $HOME/etc as ftpsync.conf and edit
it to suit your system. You should at the very least change the TO=
and RSYNC_HOST lines.
- Create $HOME/log (or wherever you point $LOGDIR to)
- Setup the .ssh/authorized_keys for the mirror user and place the public key of
your upstream mirror into it. Preface it with
no-port-forwarding,no-X11-forwarding,no-agent-forwarding,no-pty,command="~/bin/ftpsync",from="IPADDRESS"
and replace $IPADDRESS with that of your upstream mirror.
- You are finished

In order to receive different pushes or syncs from different archives,
name the config file ftpsync-$ARCHIVE.conf and call the ftpsync script
with the commandline "sync:archive:$ARCHIVE". Replace $ARCHIVE with a
sensible value. If your upstream mirror pushes you using runmirrors
bundled together with this sync script, you do not need to add the
"sync:archive" parameter to the commandline, the scripts deal with it
automatically.



Debian mirror script minimum requirements
=========================================
As always, you may use whatever scripts you want for your Debian mirror,
but we *STRONGLY* recommend you to not invent your own. However, if you
want to be listed as a mirror it *MUST* support the following minimal
functionality:

- Must perform a 2-stage sync
The archive mirroring must be done in 2 stages. The first rsync run
must ignore the index files. The correct exclude options for the
first rsync run are:
--exclude Packages* --exclude Sources* --exclude Release* --exclude ls-lR*
The first stage must not delete any files.

The second stage should then transfer the above excluded files and
delete files that no longer belong on the mirror.

Rationale: If archive mirroring is done in a single stage, there will be
periods of time during which the index files will reference files not
yet mirrored.

- Must not ignore pushes whil(e|st) running.
If a push is received during a run of the mirror sync, it MUST NOT
be ignored. The whole synchronization process must be rerun.

Rationale: Most implementations of Debian mirror scripts will leave the
mirror in an inconsistent state in the event of a second push being
received while the first sync is still running. It is likely that in
the near future, the frequency of pushes will increase.

- Should understand multi-stage pushes.
The script should parse the arguments it gets via ssh, and if they
contain a hint to only sync stage1 or stage2, then ONLY those steps
SHOULD be performed.

Rationale: This enables us to coordinate the timing of the first
and second stage pushes and minimize the time during which the
archive is desynchronized. This is especially important for mirrors
that are involved in a round robin or GeoDNS setup.

The minimum arguments the script has to understand are:
sync:stage1 Only sync stage1
sync:stage2 Only sync stage2
sync:all Do everything. Default if none of stage1/2 are
present.
There are more possible arguments, for a complete list see the
ftpsync script in our git repository.



ftpsync
=======

This script is based on the old anonftpsync script. It has been rewritten
to add flexibilty and fix a number of outstanding issues.

Some of the advantages of the new version are:
- Nearly every aspect is configurable
- Correct support for multiple pushes
- Support for multi-stage archive synchronisations
- Support for hook scripts at various points
- Support for multiple archives, even if they are pushed using one ssh key
- Support for multi-hop, multi-stage archive synchronisations

Correct support for multiple pushes
-----------------------------------
When the script receives a second push while it is running and syncing
the archive it won't ignore it. Instead it will rerun the
synchronisation step to ensure the archive is correctly synchronised.

Scripts that fail to do that risk ending up with an inconsistent archive.


Can do multi-stage archive synchronisations
-------------------------------------------
The script can be told to only perform the first or second stage of the
archive synchronisation.

This enables us to send all the binary packages and sources to a
number of mirrors, and then tell all of them to sync the
Packages/Release files at once. This will keep the timeframe in which
the mirrors are out of sync very small and will greatly help things like
DNS RR entries or even the planned GeoDNS setup.


Multi-hop, multi-stage archive synchronisations
-----------------------------------------------
The script can be told to perform a multi-hop multi-stage archive
synchronisation.

This is basically the same as the multi-stage synchronisation
explained above, but enables the downstream mirror to push his own
staged/multi-hop downstreams before returning. This has the same
advantage than the multi-stage synchronisation but allows us to do
this over multiple level of mirrors. (Imagine one push going from
Europe to Australia, where then locally 3 others get updated before
stage2 is sent out. Instead of 4times transferring data from Europe to
Australia, just to have them all updated near instantly).


Can run hook scripts
--------------------
ftpsync currently allows 5 hook scripts to run at various points of the
mirror sync run.

Hook1: After lock is acquired, before first rsync
Hook2: After first rsync, if successful
Hook3: After second rsync, if successful
Hook4: Right before leaf mirror triggering
Hook5: After leaf mirror trigger (only if we have slave mirrors; HUB=true)

Note that Hook3 and Hook4 are likely to be called directly after each other.
The difference is that Hook3 is called *every* time the second rsync
succeeds even if the mirroring needs to re-run due to a second push.
Hook4 is only executed if mirroring is completed.


Support for multiple archives, even if they are pushed using one ssh key
------------------------------------------------------------------------
If you get multiple archives from your upstream mirror (say Debian,
Debian-Backports and Volatile), previously you had to use 3 different ssh
keys to be able to automagically synchronize them. This script can do it
all with just one key, if your upstream mirror tells you which archive.
See "Commandline/SSH options" below for further details.


For details of all available options, please see the extensive documentation
in the sample configuration file.


Commandline/SSH options
=======================
Script options may be set either on the local command line, or passed by
specifying an ssh "command". Local commandline options always have
precedence over the SSH_ORIGINAL_COMMAND ones.

Currently this script understands the options listed below. To make them
take effect they MUST be prepended by "sync:".

Option Behaviour
stage1 Only do stage1 sync
stage2 Only do stage2 sync
all Do a complete sync (default)
mhop Do a multi-hop sync
archive:foo Sync archive foo (if the file $HOME/etc/ftpsync-foo.conf
exists and is configured)
callback Call back when done (needs proper ssh setup for this to
work). It will always use the "command" callback:$HOSTNAME
where $HOSTNAME is the one defined in config and
will happen before slave mirrors are triggered.

So, to get the script to sync all of the archive behind bpo and call back when
it is complete, use an upstream trigger of
ssh $USER@$HOST sync:all sync:archive:bpo sync:callback


Mirror trace files
==================
Every mirror needs to have a 'trace' file under project/trace.
The file format is as follows:

The filename has to be the full hostname (eg. hostname -f), or in the
case of a mirror participating in RR DNS (where users will never use
the hostname) the name of the DNS RR entry, eg. security.debian.org
for the security rotation)

The content has (no leading spaces):
Sat Nov 8 13:20:22 UTC 2008
Used ftpsync version: 42
Running on host: steffani.debian.org

First line: Output of date -u
Second line: Freeform text containing the program name and version
Third line: Text "Running on host: " followed by hostname -f

The third line MUST NOT be the DNS RR name, even if the mirror is part
of it. It MUST BE the hosts own name. This is in contrast to the filename,
which SHOULD be the DNS RR name.


runmirrors
==========
This script is used to tell leaf mirrors that it is time to synchronize
their copy of the archive. This is done by parsing a mirror list and
using ssh to "push" the leaf nodes. You can read much more about the
principle behind the push at [1], essentially it tells the receiving
end to run a pre-defined script. As the whole setup is extremely limited
and the ssh key is not usable for anything else than the pre-defined
script this is the most secure method for such an action.

This script supports two types of pushes: The normal single stage push,
as well as the newer multi-stage push.

The normal push, as described above, will simply push the leaf node and
then go on with the other nodes.

The multi-staged push first pushes a mirror and tells it to only do a
stage1 sync run. Then it waits for the mirror (and all others being pushed
in the same run) to finish that run, before it tells all of the staged
mirrors to do the stage2 sync.

This way you can do a nearly-simultaneous update of multiple hosts.
This is useful in situations where periods of desynchronization should
be kept as small as possible. Examples of scenarios where this might be
useful include multiple hosts in a DNS Round Robin entry.

For details on the mirror list please see the documented
runmirrors.mirror.sample file.


[1] http://blog.ganneff.de/blog/2007/12/29/ssh-triggers.html