Links on an edition are checked using the LinkChecker API. Links are checked when the Check Links button is clicked on the edition show page. This fires off a request to the Link Checker API using the /create_batch endpoint. Once this has checked all the links present in the edition it makes a callback with a batch_report that gets saved as a LinkCheckerApiReport.
The LinkCheckerApiReports are returned by the API contain a report of all the links present in an edition.
These are saved as LinkCheckerApiReportLinks. These contain information on the warnings or errors on the links, including a suggested_fix.
The LinkCheckerApiReport is displayed on the admin page with a list of the broken links found on the edition.
The CheckAllOrganisationsLinksWorker is a scheduled worker that runs nightly at 2 a.m. it queues up individual link checking tasks for each organisation using CheckOrganisationLinksWorker
CheckOrganisationLinksWorker uses the LinkCheckerApiService#check_links calls the create batch endpoint in the LinkCheckerApi. The callback and the subsequent link check report creation happen as per the on-demand check.