Upgrading to 2.0
================

Upgrading from the Munin 1.4 series to 2.0 should be quite easy.
But there are some things to take note of if you want a very smooth
transition.

The most important change is the CGI requirement.

 * Munin graphs can now generated on-demand by the web server. It is mandatory
   for the new zooming feature. The cron "munin-graph" is still the default, as
   it really ease new install and upgrading for small setups. Going the CGI road
   is recommended way if you experience performance issues with the cron setup.

 * Munin html pages may be generated on-demand by the web server. The
   default is still to run "munin-html" from cron after every update.

If you install from SVN or tar ball please make sure you read the
INSTALL file VERY carefully.

If you install from a packaged (DEB, RPM, ...) version, please make 
sure you read the specific INSTALL file VERY carefully, as there might 
be some particularities.

From Munin 1.4
-------------------------

Based on comparisons of test Munin installations on Linux
we see identical rrd file names, and rrd files are created and
structured the same way as before.  This ensures that your data
history is preserved. Upgrading to 2.0 should therefore prove to be
straightforward and cause no data loss. BUT, as hard as we tried, there 
might be a few exceptions, so YMMV.

In terms of ordering I would upgrade the master first.  If you do not
use a packaging system you may have to look around for old .pm files
and purge them to get 2.0 work properly.  Do NOT purge the RRD
files or the configuration.

After the master is upgraded upgrade the nodes one by one.  Please see
notes about changes in plugin and data-field names in the sections
below before you start upgrading the nodes.

And as one said in IRC, an old munin proverb is : "Wait two munin fetch 
rounds before you can expect to see results."

It is specially true when upgrading as the config files should auto-update
themselves, but it might take up to 2 iteration of munin-cron to be really
sorted out.

From Munin 1.2
----------------

If you still have munin-nodes running 1.2, there is no need to rush as polling
1.2 nodes from a 2.0 master is well supported.

Upgrade master straight from 1.2 isn't supported, but should work mostly well
as 2.0 is highly 1.4-compatible. But be sure to read UPGRADING-1.4 to look at
specific issues from 1.2.

Rollback
----------

Thanks to the highly 1.4-compatible status of 2.0, and our PnP-way of doing
things, rollbacking the install is very easy : just reinstall 1.4 and remove
all the *.storable files from /var/lib/munin. But don't touch the .rrd as they
ARE your history.

Then wait again for 2 munin-cron runs, and the rollback should be complete.
