Cadasta Worker Toolbox
Project description
A collection of helpers to assist in quickly building asynchronous workers for the Cadasta system.
Architecture
The Cadasta asynchronous system is designed so that both the scheduled tasks and the task results can be tracked by the central Cadasta Platform. To ensure that this takes place, all Celery workers must be correctly configured to support these features.
Tracking Scheduled Tasks
To keep our system aware of all tasks being scheduled, the Cadasta Platform has a process running to consume task messages off of a task-monitor queue and insert those messages into our database. To support this design, all task producers (including worker nodes) must publish their task messages to both the normal destination queues and the task-monitor queue. This is acheived by registering all queues with a Topic Exchange, setting the task-monitor queue to subscribe to all messages sent to the exchange, and setting standard work queues to subscribe to messages with a matching routing_key. Being that the Cadasta Platform is designed to work with Amazon SQS and the SQS backend only keeps exchange/queue declarations in memory, each message producer must have this set up within their configuration.
Tracking Task Results
TODO
Library
cadasta.workertoolbox.conf.Config
The Config class was built to simplify configuring Celery settings, helping to ensure that all workers adhere to the architecture requirements of the Cadasta asynchronous system. An instance of the Config should come configured with all Celery settings that are required by our system. It is the aim of the class to not require much customization on the part of the developer. However, some customization may be needed when altering configuration between environments (e.g. if dev settings vary greatly from prod settings).
Required Arguments
queues
The only required argument is the queues array. This should contain an array of names for queues that are to be used by the given worker. This includes queues from which the node processes tasks and queues into which the node will schedule tasks. It is not necessary to include the 'celery' or 'platform.fifo' queues, as these will be added automatically. The input of the queues variable will be stored as QUEUES on the Config instance.
Optional Arguments
Any Celery setting may be submitted. It is internal convention that we use the lowercase Celery settings rather than their older upper-case counterparts. This will ensure that they are displayed when calling repr on the Conf instance.
result_backend
TODO
task_queues
TODO
Note: It is recommended that developers not alter this setting.
task_routes
TODO
Note: It is recommended that developers not alter this setting.
Internal Variables
By convention, all variables pertinent to only the Config class (i.e. not used by Celery) should be written entirely uppercase.
RESULT_DB_USER
Variable used to populate the default result_backend template.
RESULT_DB_PASS
Variable used to populate the default result_backend template.
RESULT_DB_HOST
Variable used to populate the default result_backend template.
RESULT_DB_NAME
Variable used to populate the default result_backend template.
PLATFORM_QUEUE_NAME
Defaults to 'platform.fifo'.
Note: It is recommended that developers not alter this setting.
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