MDS Autoscaler Module
The MDS Autoscaler Module monitors fsmap
update notifications from the mgr daemon and takes action to spawn or kill MDS daemons for a file-system as per changes to the:
max_mds
config valuestandby_count_wanted
config valuestandby promotions to active MDS state in case of active MDS rank death
Bumping up the max_mds
config option value causes a standby mds to be promoted to hold an active rank. This leads to a drop in standby mds count. The MDS Autoscaler module detects this deficit and the orchestrator module is notified about the required MDS count. The orchestrator back-end then takes necessary measures to spawn standby MDSs.
Dropping the max_mds
config option causes the orchestrator back-end to kill standby mds to achieve the new reduced count. Preferably standby mds are chosen to be killed when the max_mds
count is dropped.
An increment and decrement of the standby_count_wanted
config option value has a similar effect on the total MDS count. The orchestrator is notified about the change and necessary action to spawn or kill standby MDSs is taken.
A death of an active MDS rank also causes promotion of a standby mds to occupy the required active rank. The MDS Autoscaler notices the change in the standby mds count and a message is passed to the orchestrator to maintain the necessary MDS count.
NOTE: There is no CLI associated with the MDS Autoscaler Module.