trove/doc/source/contributor/design.rst

Trove Design

High Level description

Trove is designed to support a single-tenant database within a Nova instance. There will be no restrictions on how Nova is configured, since Trove interacts with other OpenStack components purely through the API.

Trove-api

The trove-api service provides a RESTful API that supports JSON and XML to provision and manage Trove instances.

• A REST-ful component
• Entry point - trove/bin/trove-api
• Uses a WSGI launcher configured by etc/trove/api-paste.ini
• Defines the pipeline of filters; authtoken, ratelimit, etc.
• Defines the app_factory for the troveapp as trove.common.api:app_factory
• The API class (a wsgi Router) wires the REST paths to the appropriate Controllers
• Implementation of the Controllers are under the relevant module (versions/instance/flavor/limits), in the service.py module
• Controllers usually redirect implementation to a class in the models.py module
• At this point, an api module of another component (TaskManager, GuestAgent, etc.) is used to send the request onwards through RabbitMQ

Trove-taskmanager

The trove-taskmanager service does the heavy lifting as far as provisioning instances, managing the lifecycle of instances, and performing operations on the Database instance.

• A service that listens on a RabbitMQ topic

• Entry point - trove/bin/trove-taskmanager

• Runs as a RpcService configured by etc/trove/trove-taskmanager.conf.sample which defines trove.taskmanager.manager.Manager as the manager - basically this is the entry point for requests arriving through the queue

• As described above, requests for this component are pushed to MQ from another component using the TaskManager's api module using _cast() or _call() (sync/a-sync) and putting the method's name as a parameter

• In module oslo.messaging, oslo_messaging/rpc/dispatcher.py

  - RpcDispatcher.dispatch() invokes the proper method in the Manager by some equivalent to reflection

• The Manager then redirect the handling to an object from the models.py module. It loads an object from the relevant class with the context and instance_id

• Actual handling is usually done in the models.py module

Trove-guestagent

The guestagent is a service that runs within the guest instance, responsible for managing and performing operations on the Database itself. The Guest Agent listens for RPC messages through the message bus and performs the requested operation.

• Similar to TaskManager in the sense of running as a service that listens on a RabbitMQ topic

• GuestAgent runs on every DB instance, and a dedicated MQ topic is used (identified as the instance's id)

• Entry point - trove/bin/trove-guestagent

• Runs as a RpcService configured by etc/trove/trove-guestagent.conf.sample which defines trove.guestagent.datastore.manager.Manager as the manager - basically this is the entry point for requests arriving through the queue

• As described above, requests for this component are pushed to MQ from another component using the GuestAgent's api module using _cast() or _call() (sync/a-sync) and putting the method's name as a parameter

• In module oslo.messaging, oslo_messaging/rpc/dispatcher.py

  - RpcDispatcher.dispatch()invokes the proper method in the Manager by some equivalent to reflection

• The Manager then redirect the handling to an object (usually) from the dbaas.py module.

• Actual handling is usually done in the dbaas.py module

Trove-conductor

Conductor is a service that runs on the host, responsible for receiving messages from guest instances to update information on the host. For example, instance statuses and the current status of a backup. With conductor, guest instances do not need a direct connection to the host's database. Conductor listens for RPC messages through the message bus and performs the relevant operation.

• Similar to guest-agent in that it is a service that listens to a RabbitMQ topic. The difference is conductor lives on the host, not the guest.
• Guest agents communicate to conductor by putting messages on the topic defined in cfg as conductor_queue. By default this is "trove-conductor".
• Entry point - trove/bin/trove-conductor
• Runs as RpcService configured by etc/trove/trove-conductor.conf.sample which defines trove.conductor.manager.Manager as the manager. This is the entry point for requests arriving on the queue.
• As guestagent above, requests are pushed to MQ from another component using _cast() (synchronous), generally of the form {"method": "<method_name>", "args": {<arguments>}}
• Actual database update work is done by trove/conductor/manager.py
• The "heartbeat" method updates the status of an instance. This is used to report that instance has changed from NEW to BUILDING to ACTIVE and so on.
• The "update_backup" method changes the details of a backup, including its current status, size of the backup, type, and checksum.