Asynchronous Task Processor

Flagsmith has the ability to consume asynchronous tasks using a separate task processor service. If flagsmith is run without the asynchronous processor, the flagsmith API will run any asynchronous tasks in a separate, unmanaged thread.

Running the Processor

The task processor can be run using the flagsmith/flagsmith-api image with a slightly different entrypoint. It should be pointed to the same database that the API container is using. To enable the API sending tasks to the processor, you must set the TASK_RUN_METHOD to TASK_PROCESSOR in the flagsmith container running the flagsmith application.

A basic docker-compose setup might look like:

    postgres:
        image: postgres:11.12-alpine
        environment:
            POSTGRES_PASSWORD: password
            POSTGRES_DB: flagsmith
        container_name: flagsmith_postgres

    flagsmith:
        image: flagsmith/flagsmith-api
        environment:
            DJANGO_ALLOWED_HOSTS: '*'
            DATABASE_URL: postgresql://postgres:password@postgres:5432/flagsmith
            ENV: prod
            TASK_RUN_METHOD: TASK_PROCESSOR
        ports:
            - '8000:8000'
        depends_on:
            - postgres
        links:
            - postgres

   flagsmith_processor:
       build:
           dockerfile: api/Dockerfile
           context: .
       environment:
           DATABASE_URL: postgresql://postgres:password@postgres:5432/flagsmith
       command:
           - run-task-processor
       depends_on:
           - flagsmith
           - postgres

Configuring the Processor

The processor exposes a number of configuration options to tune the processor to your needs / setup. These configuration options are via command line arguments when starting the processor.

Argument	Description	Default
--sleepintervalms	The amount of ms each worker should sleep between checking for a new task	2000
--numthreads	The number of worker threads to run per task processor instance	5
--graceperiodms	The amount of ms before a worker thread is considered 'stuck'.	20000

Monitoring

There are a number of options for monitoring the task processor's health.

Checking Thread / Worker Health

The task processor includes a management command which checks the health of the worker threads which are running tasks.

python manage.py checktaskprocessorthreadhealth

The command will exit with either a success exit code (0) or a failure exit code (1).

API to Task Processor health

To monitor that the API can send tasks to the processor and that they are successfully run, there is a custom health check which can be enabled on the general health endpoint (GET /health?format=json). This health check needs to be enabled manually, which can be done by setting the ENABLE_TASK_PROCESSOR_HEALTH_CHECK environment variable to True (in the flagsmith application container, not the task processor). Note that this health check is not considered "critical" and hence, the endpoint will return a 200 OK regardless of whether the task processor is sucessfully processing tasks or not.

Task statistics

Within the API, there is an endpoint which returns, in JSON format, statistics about the tasks consumed / to be consumed by the processor. This endpoint is available at GET /processor/monitoring. This will respond with the following data:

{
 "waiting": 1
}