09.11.2016 10:59, Ulrich Windl wrote:
Ken Gaillot <kgail...@redhat.com> schrieb am 08.11.2016 um 18:16 in Nachricht
<92c4a0de-33ce-cdc2-a778-17fddfe63...@redhat.com>:
On 11/08/2016 03:02 AM, Ulrich Windl wrote:
[...]
The user is responsible for choosing meaningful values. For example, if
node-health-base is +10 but yellow is -15, then any yellow attribute
will still push resources away. Of course, that could still be
meaningful when combined with other scores -- someone might do that if
they want a location preference of +5 to counteract a single yellow
attribute. Or maybe instead of node-health-base, someone sets a positive
stickiness, so existing resources can stay on a yellow node, but new
resources won't be placed there. It can be as simple or complicated as
you want to get :)
I think it's too complicated, already: In my simple world nodes with
status "green" are OK to run any resource, nodes with status "yellow"
should not start new resources, and nodes with status "red" should move
away running resources. Ok, I see the some people have a desire for
"orange", "indian yellow" and a lots of different colors on the
spectrum, but thinking of the seemingly endless cases to test, I prefer
a simple world ;-)
That was implemented mainly to allow drbd (among other replicated
datastores) to be started as a secondary on a node with yellow
attributes. That attributes come from outside of pacemaker and actually
may have any meaning one may imagine. In our case we utilized new alerts
feature to manage specific yellow attributes if resources repeatedly
fail and recover, something similar to a flapping detection in nagios.
So all services go away from a node with the worst health score, making
another node "active" one. But we still wanted to have secondary data
replica online and in sync.
The first attempt was to set positive "base" health attribute from a
resource agent, but then we realized that resource won't start (rather
expected, like every other resource) after node with some yellow
attributes was brought back from the standby mode.
So the decision was made to submit a 5-line patch for pacemaker ;)
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