109 lines
4.2 KiB
ReStructuredText
109 lines
4.2 KiB
ReStructuredText
====================
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Vitrage Graph Design
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====================
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.. image:: ./images/low_level_design.png
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:width: 100%
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:align: center
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Main Components
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===============
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Graph
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-----
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A library with a graph representation, that is used by Vitrage Graph and by
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Vitrage Evaluator.
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The **Graph Driver** consists of APIs for graph CRUD operations (add/remove
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vertex, add/remove edge, etc.) and graph algorithms for iteration and pattern
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detection. In Mitaka, the graph driver will be implemented in-memory over
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NetworkX (https://networkx.github.io/). Future versions should support
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replacing NetworkX with a persistent graph DB such as Titan or Neo4J.
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Datasources
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-----------
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Vitrage can support multiple *datasources* to populate its graph. Each
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datasource is responsible for importing information regarding certain entities
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in the cloud and defining how to integrate their information into the graph.
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Entities in this context refer both to resources (physical & virtual) and
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alarms (Aodh, Nagios, Monasca, etc.)
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The datasource is comprised of two components. The *Driver* handles retrieving
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the information and entering it into the entity queue, while the *Transformer*
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defines how to integrate the information retrieved into the graph (for more
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details about the Transformer, see next section).
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The datasource *driver* has two modes of operation:
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- *get_all* (snapshot): Pull-based operation. Query all entities for this
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datasource and send events to the queue. When done, send an "end" event.
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- *notify*: Push-based operation. When change occurs, send an event to the
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queue.
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Entity Processor and Transformers
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---------------------------------
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The Entity Processor is responsible for polling events from the entity queue
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and inserting corresponding vertices to the Graph. For every entity event in
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the queue, the Processor calls the Transformer that is registered on this
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entity type. For each datasource there is a Transformer, which understands the
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specific entity details. It queries the graph, and after processing outputs a
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vertex to be inserted to the Graph together with edges that connect it to its
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neighbors in the graph.
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Evaluator
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---------
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The Evaluator is notified on every change in the Graph, and is responsible for
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executing templates that are related to this change.
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Template Examples:
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- Deduced alarm: In case an alarm is raised indicating a public switch is down,
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trigger an "instance is at risk" alarm on every instance that is contained by
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a host attached to this switch.
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- Deduced state: In case an alarm is raised indicating a public switch is down,
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set the state of every instance that is contained by a host attached to this
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switch to be "suboptimal".
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- Causal relationship: In case an alarm is raised indicating a public switch is
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down, and an "instance is at risk" alarm is active on an instance that is
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contained by a host attached to this switch - determine that the switch alarm
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is the root cause of the instance alarm, and add a "causes" edge to the Graph
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from the vertex representing the switch to the vertex representing the
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instance.
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Templates can be added, removed or modified by the user.
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Consistency
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-----------
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This component is responsible for verifying the Graph's consistency with the
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actual situation in the cloud. It is called both during Vitrage startup, as
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part of the graph initialization, as well as periodically to ensure the graph
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is correct.
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The consistency component will include:
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- Deleting obsolete vertices
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- Handle the case that Vitrage missed a "delete entity" event, and did not
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delete certain deduced alarms.
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- Ensure no entity is missed in the Graph. This can be done by retrieving all
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entities from all datasources.
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**Note:** If an entity is added, its related templates will also be executed
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as well to create deduced alarms and add RCA information to the graph.
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API Handler
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-----------
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The API handler is responsible for transferring Vitrage API calls to the Graph.
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Notifiers
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---------
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The notifier is responsible for notifying registered external components of
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changes that took place in the graph. For example, external OpenStack projects
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such as Aodh/Monasca could have a notifier to notify them about deduced alarms.
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Each notifier is responsible to notify another component.
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