Default filters

https://blueprints.launchpad.net/searchlight/+spec/overridable-default-filters

This spec is proposed to support cases in plugins where a filter should be applied for most searches, but should be overidable by a user.

Problem Description

The two cases identified thus far for supporting default (but overridable) filters are glance’s community images, and nova deleted server instances. In both cases there are query clauses that should be applied to searches by default, but which a user should be able to explicitly disable.

Proposed Change

In addition to RBAC filters which are applied to all queries on a per-plugin basis, this change will allow plugins to specify additional filters that will be applied by default alongside the RBAC filters. For these defaults, however, the query builder will examine the incoming query for any instances of the fields that would be filtered on, excluding any filters that the user has explicitly specified.

This solution will have some flaws. query_string clauses are by their nature difficult to analyze; potentially we can look for instances of key: after splitting on &. For structured queries, looking for instances of the filter key in the structured query should be good enough.

In addition, it will be difficult/impossible to know whether a filter should be overridden only for specific types (e.g. if deleted is a default filter for the Nova servers plugin, it will be removed for any query including deleted as a term even if it wasn’t intended to apply to Nova servers).

These limitations are somewhat unavoidable given the flexibility of the Elasticsearch DSL. The cases for removing these filters are specific enough that edge cases aren’t important.

Alternatives

None, but this restricts the use of Searchlight for Nova’s cells, and the ability to match Glance’s API with respect to community images.

An alternative implementation option would be a specific option for ‘disable default filters’ at the query top level. This would be safer, more performant, more predictable but would require knowledge of these defaults (e.g. that a search for _type:OS::Nova::Server AND deleted won’t return anything unless the additional override parameter is given).

References

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