openhim-core/docs/user-guide/polling-channels.md

The OpenHIM core application that provides logging and routing of http requests

Polling Channels (scheduled tasks)
==================================

A great feature of the OpenHIM is the ability to trigger tasks in other systems.
This is made possible by a special type of channel called a polling channel. Polling
channels are channels that the OpenHIM will trigger internally on some sort of
schedule. When a channel is triggered it will cause each of the routes that are
configured for that channel to execute.

The OpenHIM will trigger the polling channel with a `GET` request to the `/trigger`
path on the defined schedule. Each route can override the path with their own as
long as they are configured with a path. External systems can be triggered by
pointing a route at them. The external systems will have to expose an HTTP
endpoint for them to be triggered. The triggering will always happen as an HTTP
`GET` request.

To configure a polling channel, in the console click on 'Channels' on the menu,
choose add channel and set the type of the channel to 'polling'. You will be able
to provide a schedule for the polling channel to be executed. You may provide this
in cron format (ie. 0 4 * * * ) or in a descriptive format (ie. 5 minutes). See
[the agenda documentation](https://github.com/rschmukler/agenda#everyinterval-name-data-options-cb)
for a more complete description of this format. From there you may configure the
rest of the channel as usual and add routes for each external system that is to
be triggered.

**NB** When using cron format, it is important to note that the servers' timezone will be used to action the trigger