watcher-specs/specs/stein/implemented/scope-for-watcher-datamodel.rst

Adding scope for Watcher data model

https://blueprints.launchpad.net/watcher/+spec/scope-for-watcher-datamodel

Problem description

For a large cloud infrastructure, such as CERN, there are more than 10k servers, retrieving data from Nova to build Watcher compute data model may take a long time. If the audit is just for a subset of all nodes, it's better to get the data from the nodes that audit needs.

Use Cases

As a Watcher user, I want that Watcher doesn't build compute data model before creating audit. As a Watcher user, I want that Watcher build compute data model according to the scope of audit.

Proposed change

As now, Watcher builds compute data model when starting the Decision Engine. And there is a periodic task to rebuild the data model. To avoid building the data model before creating audit, we need to check a flag before building the data model. for example:

def execute(self):
    """Build the compute cluster data model"""
    if self._audit_scope_handler is None:
        LOG.debug("No audit, Don't Build compute data model")
        return

    builder = ModelBuilder(self.osc)
    return builder.execute(self._data_model_scope)

Audit scope is a optional parameter when creating audit. If user don't set a scope ,the default scope is empty, it means this audit used for all nodes. An example of the audit scope:

{"compute":
    [{"host_aggregates": [
                          {"id": 1},
                          {"id": 2},
                          {"id": 3}]},
     {"availability_zones": [
                          {"name": "AZ1"},
                          {"name": "AZ2"}]},
}

When building the data model according to audit scope, there are some cases need to be considered:

no data model, audit scope is empty

• It's the first time to build the data model. Because audit scope is empty, the data model should include all the nodes.

no data model, audit scope is not empty

• It's the first time to build the data model according to audit scope.

Existing data model, new audit scope is empty

• If the data model has included all nodes, it will not be rebuilt.
• If the data model doesn't include all nodes, it will be rebuilt.

existing data model, new audit scope is not empty

• If the nodes specified in scope are already included in the data model, it will not be rebuilt.
• If the nodes specified in the scope aren't included in the data model, it will be rebuilt.

Alternatives

None

Data model impact

None

REST API impact

None

Security impact

None

Notifications impact

None

Other end user impact

None

Performance Impact

This will reduce the impact on system performance, especially for large cloud infrastructure.

Other deployer impact

None

Developer impact

None

Implementation

Assignee(s)

Primary assignee:

<licanwei>

Work Items

• Add a check to the audit to create before building the data model.
• Add the model scope to record the audit scope in the ModelBuilder class.
• Update the data model according to the audit scope.

Dependencies

None

Testing

Add unit tests.

Documentation Impact

Update Watcher developer documents.

References

None

History

Revisions

Release Name	Description
Stein	Introduced