Revision 99721eb4 doc/design-virtual-clusters.rst

b/doc/design-virtual-clusters.rst
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|networking     |                       |with an existing bridge at system   |
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|               |                       |level or use NIC-less instances     |
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+---------------+-----------------------+------------------------------------+
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|instance OS    |OS add, OS rename,     |Only used with non diskless         |
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|instance OS    |OS add, OS rename,     |Only used with non-diskless         |
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|operations     |export and import      |instances; could work with custom OS|
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|               |                       |scripts (that just ``dd`` without   |
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|               |                       |scripts that just ``dd`` without    |
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|               |                       |mounting filesystems                |
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+---------------+-----------------------+------------------------------------+
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|node networking|IP address management  |Not supported; Ganeti will need to  |
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|               |(master ip), IP query, |work without a master IP. For the IP|
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|               |etc.                   |query operations, the test machine  |
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|               |(master ip), IP query, |work without a master IP; for the IP|
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|               |etc.                   |query operations the test machine   |
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|               |                       |would need externally-configured IPs|
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+---------------+-----------------------+------------------------------------+
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|node add       |-                      |SSH command must be adjusted        |
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+---------------+-----------------------+------------------------------------+
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|node setup     |ssh, /etc/hosts, so on |Can already be disabled from the    |
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|               |                       |cluster config                      |
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+---------------+-----------------------+------------------------------------+
......
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An alternative option is to implement per-node IP/port support in Ganeti


  		





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(especially in the RPC layer), which would eliminate the root rights. We


  		





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expect that this will get implemented as a second step of this design.


  		





  
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expect that this will get implemented as a second step of this design,


  		





  
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but as the port is currently static will require changes in many places.


  		





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The only remaining problem is with sharing the ``localstatedir``


  		





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structure (lib, run, log) amongst the daemons, for which we propose to


  		





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add a command line parameter which can override this path (via injection


  		





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into ``_autoconf.py``). The rationale for this is two-fold:


  		





  
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introduce an environment variable (``GANETI_ROOTDIR``) acting as a


  		





  
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prefix for essentially all paths. An environment variable is easier to


  		





  
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transport through several levels of programs (shell scripts, Python,


  		





  
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etc.) than a command line parameter. In Python code this prefix will be


  		





  
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applied to all paths in ``constants.py``. Every virtual node will get


  		





  
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its own root directory. The rationale for this is two-fold:


  		





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- having two or more node daemons writing to the same directory might


  		





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  introduce artificial scenarios not existent in real life; currently


  		





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  daemon wrote a file successfully, the results from all others are


  		





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  “lost”


  		





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In case the use of an environment variable turns out to be too difficult


  		





  
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a compile-time prefix path could be used. This would then require one


  		





  
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Ganeti installation per virtual node, but it might be good enough.


  		





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``rapi``


  		





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--------


  		





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----------------------


  		





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It could be possible that the cluster initialisation procedure is a bit


  		





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more involved (this was not tried yet). In any case, we can build a


  		





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``config.data`` file manually, without having to actually run


  		





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``gnt-cluster init``.


  		





  
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more involved (this was not tried yet). A script will be used to set up


  		





  
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all necessary IP addresses and hostnames, as well as creating the


  		





  
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initial directory structure. Building ``config.data`` manually should


  		





  
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not be necessary.


  		





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Needed tools


  		





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============


  		





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are:


  		





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- a tool to setup per-virtual node tree structure of ``localstatedir``


  		





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  and setup correctly the extra IP/hostnames


  		





  
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  (with the help of ``ensure-dirs``) and setup correctly the extra


  		





  
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  IP/hostnames


  		





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- changes to the startup daemon tools to launch correctly the daemons


  		





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  per virtual node


  		





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- changes to ``noded`` to override the ``localstatedir`` path


  		





  
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- changes to ``constants.py`` to override the ``localstatedir`` path


  		





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- documentation for running such a virtual cluster


  		





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- and eventual small fixes to the node daemon backend functionality, to


  		





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  better separate privileged and non-privileged code


  		












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