Asyncable Models

History

The problem: external calls to VBMS and BGS can take a long time to run, and sometimes they fail due to a variety of reasons. This caused problems for our users, who had to wait for the tasks to run and then re-do work if they failed through no fault of their own.

So we decided to audit our Intake-related models and move all our external service calls to run asynchronously, in the background. They also needed to be idempotent, so that retries would not create duplicate data.

We already have ActiveJob and the shoryuken (https://github.com/phstc/shoryuken) gem for handing cron and background tasks. It's configured to automatically retry jobs in a progressively decaying interval https://github.com/department-of-veterans-affairs/caseflow/blob/master/config/initializers/shoryuken.rb#L8

Our dilemma was that sometimes external services go down for hours, and we wanted a retry interval that stretched into days. Also, we wanted to be able to query the database to see the status of these tasks.

Implementation

What we hit on was an asynchronous pattern that uses both shoryuken to run outside the web process and the database for state persistence.

https://github.com/department-of-veterans-affairs/caseflow/blob/master/app/models/concerns/asyncable.rb

The Asyncable concern requires 6 columns be added to any ActiveRecord model:

• submitted_at
• last_submitted_at
• attempted_at
• processed_at
• canceled_at
• error

The naming is flexible -- you can override the default column names with class methods in the consuming model.

Models with the Asyncable concern will also inherit this association with job_notes:

has_many :job_notes, as: :job

The Asyncable concern adds a variety of class scope methods for querying categories of tasks that run in the background.

By default, tasks run every 3 hours and will expire after 4 days.

We use those scoping methods in a cron job: https://github.com/department-of-veterans-affairs/caseflow/blob/master/app/jobs/sync_reviews_job.rb

to fire off shoryuken jobs: https://github.com/department-of-veterans-affairs/caseflow/blob/master/app/jobs/decision_review_process_job.rb

Admin

There is a /jobs page in the Caseflow app that allows users to view all the "potentially stuck" (running, queued or expired) jobs. Each job has a detail page as well, linked from the main /jobs by path of "/asyncable_jobs/#{self.class}/jobs/#{id}". A example link would be https://appeals.cf.ds.va.gov/asyncable_jobs/SupplementalClaim/jobs.