Overcommiting CPU and Memory on Node Controllers

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Eucalyptus Versions:  3.0 and above.

Introduction

By default Eucalyptus Node Controllers use a 1:1 overcommit ratio for both CPU and Memory, that is to say there is no overcommit out of the box.  It is possible to change this behaviour.

NOTE: Caution should be applied when modifying these settings.  Incorrect planning and overcommit of resources could result in bad stuff, including but not limited to: earthquakes, tsunamis, black holes.

Configuration Example

Two properties exist or are parsed in the /etc/eucalyptus/eucalyptus.conf file: MAX_CORES and MAX_MEM.  If you wish to overcommit CPU by a 2:1 ratio on an 8 core box would you set MAX_CORES to 16.  If you wish to follow the same ratio with memory on a box with 64GB of memory, you would set MAX_MEM to 128GB.  The value for MAX_CORES is the number of cores the Node Controller advertises as available.  The value for MAX_MEM is the amount of advertised memory, in MB.  In this example, these values would be set as:

MAX_CORES="16"

MAX_MEM="131072"  

131072MB since 128(GB) x 1024 = 131072.

The Node Controller should be restarted for this change to take effect:

# service eucalyptus-nc restart

References

 

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