[Maas-devel] MAAS Power states

[Christian Robottom Reis]

Hello Carla,

    Just summarizing the discussion we had on power states, and thinking
a bit further, from the user's perspective I think there are 4, perhaps
5 useful power states:

    1 No power parameters configured
    2 Power on
    3 Power off
    4 Power check failed
        (because the power parameters are wrong, or another failure
         to check)
    5 Power never checked

Informing the user of state 1 is useful because he then knows he needs
to go ahead and configure power parameters (for instance, if they were
not auto-detected as is the case with AMT).

States 2 and 3 are obviously useful.

State 4 is useful because again, there is user intervention required;
the user can fix power parameters or verify if there is a networking
issue between MAAS and the node controller. It could also be a bug in
MAAS, which also requires intervention (the filing of a bug).

State 5 exists as an artifact of our current implementation, where the
power check is not guaranteed to have happened when we display the
machine in a listing or view. It may become less relevant if we ensure
that we check power immediately after power parameters are configured.

States 1, 4 and 5 above are an effective "power state unknown" to the
end-user. But I think they are more useful to communicate than a plain
unknown.

You asked about "power check ok" and "power check error" but those
states are not really power states, but rather results of a power check
operation. I'm not sure what context you are asking in, but they are
important pieces of feedback to the end-user when a manual power check
is issued. In a bit more detail:

    - The power state may be out of sync with reality.
        - The power state may never have been checked.
        - Also, while we check power at frequent intervals, there is
          always the possibility that the machine has lost power (or
          started up) independently of MAAS.
    - For that reason, the user can request at any time a power check
      which is triggered immediately, IF there are power parameters
      configured for the node.
    - That power check can either fail or succeed.
    - If it succeeds, then the power state of the machine will be set to
      either 2 or 3 above.
    - If it fails, the power state of the machine should be set to 4.

Let me know if you have any further questions. Thanks,
-- 
Christian Robottom Reis   | [+1] 612 888 4935    | http://launchpad.net/~kiko
Canonical VP Hyperscale   | [+55 16] 9 9112 6430