I want to start a dialog around adding some usability features to Savanna, now
that I have had a chance to spend a fair amount of time provisioning, scaling
and changing clusters. Here is a list of items that I believe are important to
address; comments welcomed:
1. Changing an OpenStack flavor associated with a node-group template has a
ripple effect on both node group and cluster templates. The reason for this is
that OpenStack does not support modification of flavors; when a flavor is
modified (RAM, CPU, Root Disk, etc.) the flavor is deleted and a new one is
created resulting in a new flavor id. The implication is that both node-group
referencing the flavor [id] and any cluster templates referencing the affected
node-group become stale and unusable. A user then has to start from scratch,
creating new node-groups and cluster templates for a simple flavor change.
a. A possible solution to this is to internally associate flavor
name with node-group and look up the flavor id based on flavor name when
provisioning instances
b. At a minimum it should be possible to change the flavor id
associated with a node-group. See #2.
2. Cluster templates and node group templates are immutable. This is more of
an issue at the node-group level as I often times want to make changes to a
node-group and want to affect all cluster templates that make use of that
node-group. I see this as being fairly commonplace.
3. Before provisioning a cluster, quotas should be checked to make sure that
enough quota exists. I know this can be done transactionally (check quota,
spawn cluster), but a basic check would go a long way.
4. Spawning a large cluster comes with some problems today, as Savanna will
abort if a single VM fails. In deploying large clusters (100’s to x1000), which
will be commonplace, having a single slave VM (i.e. data node) not spawn
properly should not necessarily be a reason to abort the entire deployment, in
particular in a scaling operation. Obviously the failing VM cannot be a master
service. This applies both to the plugin as well as controller as they are both
involved in the deployment. I could see a possible solution being the creation
of an error/fault policy allowing a user to specify (perhaps optionally) a % or
hard number for minimum # of nodes that need to come up without aborting
deployment.
a. This also applies to scaling the cluster by larger increments
Just some thoughts based on my experience last week; comments welcomed.
Best,
Erik
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