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Re: [Cluster-devel] cluster3 config system



On Mon, 23 Jun 2008, David Teigland wrote:

It seems there's been some confusion about what the config system (ccs
replacement) should be and do in cluster3.  There were just two ideas I
offered way back at the beginning:

1. Move the update mechanism outside the config system.

2. What remains is the part that reads the local cluster.conf file.
  This small and simple remainder should be merged into cman.

This is a bit more clear than what we originally discussed and can be easily achieved by modifing ccsconfig.lcrso. Loading the config from the file is dead easy. The problem to notify nodes about updates needs some investigation from my side because it might add an extra tool/interface to an existing tool. _Maybe_ we can even consider using some fancy interfaces like inotify to detect a config change and propagate across the cluster.

In any case cman will never read the config directly. It would be the "ccsais" plugin doing it (can be renamed to fileconfig or whatever..), mainly because we don't want cman to become "Alpha and Omega".

If we move the config loader within ccsais, the actual ccsd can be either removed, or turned into an "update mechanism" only. There would be tons of unrequired code that can disappear from ccsd and it would become a realitevely slim daemon to have around (optional and only for who wants it).

Another idea that emerged was,

3. Add the option to get cluster.conf from an LDAP server.

This was a requirement from customers AFAIK.

My impression, from casually following the progress, was that 2 and 3 were
largely done, but I wasn't sure what the status of 1 was.

In order to achieve 1,2 and 3 we had to modularize and abstract a lot of bits. All the abstraction layer and modularization is done.

It is possible to replace ccsd with "something else" but that something else needs to be written (like LDAP config loader). Theoretically speaking you can use openais config file and format right now to load a replacement for cluster.conf.

There aren't any cluster2 (RHEL5) compatibily issues here.  cluster2 and
cluster3 nodes can coexist in a cluster just fine as long as they are
using matching cluster.conf files.

This is a strong assumption IMHO.

The same moment in which you advertise backward compatibility, you can expect people to switch a bunch of nodes from 2 to 3 in the same cluster to test services and so on. That might involve configuration changes as well. If there is no common update mechanism, the user experience will be aweful.

The big picture (as i see it) is a bit more complicated and i see a lot of corner cases where it desirable to change configs on the fly in a mixed cluster.

Fabio

--
I'm going to make him an offer he can't refuse.


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