Synnefo » snf-ganeti

Node flags

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Current state and shortcomings

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Currently all nodes are, from the point of view of their capabilities,

homogeneous. This means the cluster considers all nodes capable of

becoming master candidates, and of hosting instances.

This prevents some deployment scenarios: e.g. having a Ganeti instance

(in another cluster) be just a master candidate, in case all other

master candidates go down (but not, of course, host instances), or

having a node in a remote location just host instances but not become

master, etc.

Proposed changes

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Two new capability flags will be added to the node:

- master_capable, denoting whether the node can become a master

  candidate or master

- vm_capable, denoting whether the node can host instances

In terms of the other flags, master_capable is a stronger version of

"not master candidate", and vm_capable is a stronger version of

"drained".

For the master_capable flag, it will affect auto-promotion code and node

modifications.

The vm_capable flag will affect the iallocator protocol, capacity

calculations, node checks in cluster verify, and will interact in novel

ways with locking (unfortunately).

It is envisaged that most nodes will be both vm_capable and

master_capable, and just a few will have one of these flags

removed. Ganeti itself will allow clearing of both flags, even though

this doesn't make much sense currently.