Eucalyptus Versions: 3.0 and above.
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.
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:
131072MB since 128(GB) x 1024 = 131072.
The Node Controller should be restarted for this change to take effect:
# service eucalyptus-nc restart