Decommission of specific instance

Decommission of specific instance

https://blueprints.launchpad.net/sahara/+spec/decommission-specific-instance

When facing issues with a cluster it can be useful to remove an specific instance. The way that Sahara is constructed today allows the user to scale a cluster down but it will choose a random instance from the selected node group to be removed. We want to give the users the opportunity to choose which instance(s) he/she would like to remove from the cluster.

Problem description

Users may need to remove specific node to make cluster healthier. This is not possible today.

Proposed change

We will add the possibility for the user to choose the specific instance to remove from the cluster.

After selecting the node group from which the instance will be removed the user will be allowed to choose the instance or instances to be removed.

We will also allow wildcard removal, if the user wants to randomly select the instance he can just leave it blank as well as if more than one instance is being deleted the user will be able to choose each instance to be deleted or just a subset and Sahara will choose the rest.

Alternatives

Keep randomly selecting instance to be scaled down.

Data model impact

None

REST API impact

We will change the body request for scale cluster.

Currently the body should be like this:

{
“add_node_groups”: [
{
“count”: 1, “name”: “b-worker”, “node_group_template_id”: “bc270ffe-a086-4eeb-9baa-2f5a73504622”

}

],

“resize_node_groups”: [
{
“count”: 4, “name”: “worker”

}

]

}

We will change the second part to support an extra parameter:

{
“add_node_groups”: [
{
“count”: 1, “name”: “b-worker”, “node_group_template_id”: “bc270ffe-a086-4eeb-9baa-2f5a73504622”

}

],

“resize_node_groups”: [
{
“count”: 4, “name”: “worker”, “instances”: [“instance_id1”, “instance_id2”]

}

]

}

In case the user does not specify instances to be removed the parameter will not be passed and we will act on removing with the current approach.

Other end user impact

CLI command will have a new option to select instances.

Deployer impact

None

Developer impact

None

Sahara-image-elements impact

None

Sahara-dashboard / Horizon impact

We will need to add a place for user to select the instances to be removed. It can be after the NG selection and we add the number of selector of instances to be removed with the option to leave it blank.

Implementation

Assignee(s)

Primary assignee:
Telles Nobrega
Other contributors:
None

Work Items

  • Add the possibility to select an instance when scaling down
  • Add CLI option to select instances to be removed
  • Add UI option to select instances to be removed
  • Unit tests
  • Documentation

Dependencies

None

Testing

Unit tests will be needed.

Documentation Impact

Nothing out of the ordinary, but important to keep in mind both user and developer perspective.

References

None

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sahara-specs