Merge "Add config file format docs"
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[gerrit]
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host=review.openstack.org
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port=29418
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project=stackforge/stacktach-stackdistiller.git
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README.md
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README.md
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stackdistiller
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==============
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# stackdistiller
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A data extraction and transformation library for OpenStack notifications.
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Stackdistiller is designed to extract data from openstack notifications
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and convert it into a form relevant to the application consuming the
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notification. It consists of two components, the Distiller, which extracts
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data from notifications according to a YAML config file, and the Condenser,
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which receives the data extracted by the Distiller, and formats it into
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an application-specific object, referred to as an Event. This could be a
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simple python dictionary, an XML document tree, or a set of ORM model
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objects.
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data from notifications according to a YAML [config file](doc/event_definitions_config.md),
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and the Condenser, which receives the data extracted by the Distiller,
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and formats it into an application-specific object, referred to as an Event.
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This could be a simple python dictionary, an XML document tree, or a set of
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ORM model objects.
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## Distiller
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Event Definitions YAML Config Format
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====================================
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# Event Definitions file format
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Documentation to go here soon.
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The event definitions file is in YAML format. It consists of a list of event
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definitions, which are mappings. Order is significant, the list of definitions
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is scanned in *reverse* order (last definition in the file to the first),
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to find a definition which matches the notification's event_type. That
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definition will be used to generate the Event. The reverse ordering is done
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because it is common to want to have a more general wildcarded definition
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(such as `compute.instance.*` ) with a set of traits common to all of those
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events, with a few more specific event definitions (like
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`compute.instance.exists`) afterward that have all of the above traits, plus
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a few more. This lets you put the general definition first, followed by the
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specific ones, and use YAML mapping [merge key syntax](http://yaml.org/type/merge.html)
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to avoid copying all of the trait definitions.
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## Event Definitions
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Each event definition is a mapping with two keys (both required):
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event_type
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This is a list (or a string, which will be taken as a 1 element list)
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of event_types this definition will handle. These can be
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wildcarded with unix shell glob syntax. An exclusion listing
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(starting with a '!') will exclude any types listed from matching.
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If ONLY exclusions are listed, the definition will match anything
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not matching the exclusions.
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traits
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This is a mapping, the keys are the trait names, and the values are
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trait definitions.
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## Trait Definitions
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Each trait definition is a mapping with the following keys:
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type
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(optional) The data type for this trait. (as a string). Valid
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options are: text, int, float, and datetime.
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defaults to text if not specified.
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fields
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A path specification for the field(s) in the notification you wish
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to extract for this trait. Specifications can be written to match
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multiple possible fields, the value for the trait will be derived
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from the matching fields that exist and have a non-null values in
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the notification. By default the value will be the first such field.
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(plugins can alter that, if they wish). This is normally a string,
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but, for convenience, it can be specified as a list of
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specifications, which will match the fields for all of them. (See
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"Field Path Specifications" below for more info on this syntax.)
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plugin
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(optional) This is a mapping (For convenience, this value can also
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be specified as a string, which is interpreted as the name of a
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plugin to be loaded with no parameters) with the following keys
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name
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(string) name of a plugin to load
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parameters
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(optional) Mapping of keyword arguments to pass to the plugin on
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initialization. (See documentation on each plugin to see what
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arguments it accepts.)
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## Field Path Specifications
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The path specifications define which fields in the JSON notification
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body are extracted to provide the value for a given trait. The paths
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can be specified with a dot syntax (e.g. `payload.host`). Square
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bracket syntax (e.g. `payload[host]`) is also supported. In either
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case, if the key for the field you are looking for contains special
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characters, like '.', it will need to be quoted (with double or single
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quotes) like so:
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payload.image_meta.'org.openstack__1__architecture'
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The syntax used for the field specification is a variant of JSONPath,
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and is fairly flexible. (see: https://github.com/kennknowles/python-jsonpath-rw for more info)
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## Example Definitions file
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---
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- event_type: compute.instance.*
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traits: &instance_traits
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user_id:
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fields: payload.user_id
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instance_id:
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fields: payload.instance_id
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host:
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fields: publisher_id
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plugin:
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name: split
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parameters:
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segment: 1
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max_split: 1
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service_name:
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fields: publisher_id
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plugin: split
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instance_type_id:
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type: int
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fields: payload.instance_type_id
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os_architecture:
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fields: payload.image_meta.'org.openstack__1__architecture'
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launched_at:
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type: datetime
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fields: payload.launched_at
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deleted_at:
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type: datetime
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fields: payload.deleted_at
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- event_type:
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- compute.instance.exists
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- compute.instance.update
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traits:
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<<: *instance_traits
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audit_period_beginning:
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type: datetime
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fields: payload.audit_period_beginning
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audit_period_ending:
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type: datetime
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fields: payload.audit_period_ending
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## Trait plugins
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Trait plugins can be used to do simple programmatic conversions on the value in
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a notification field, like splitting a string, lowercasing a value, converting
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a screwball date into ISO format, or the like.
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Plugins are initialized with the parameters from the trait definition, if any,
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which can customize their behavior for a given trait.
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They are called with a list of all matching fields from the notification,
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so they can derive a value from multiple fields.
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The plugin will be called even if there is no fields found matching the field
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path(s), this lets a plugin set a default value, if needed.
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A plugin can also reject a value by returning `None`, which will cause the trait not to be
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added.
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If the plugin returns anything other than `None`, the trait's value
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will be set from whatever the plugin returned (coerced to the appropriate type
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for the trait).
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