An HTTP trigger enables you to monitor a URI for changes by checking for changes to the Last-Modified and Content-MD5 HTTP header fields. You can configure the polling interval, and you can optionally set the start and expiry date of the trigger. The screenshot below (with UI opened in Firefox) illustrates how to define the settings of a HTTP trigger.
The trigger is defined with the help of the following parameters:
•Name: The trigger's name is a string that serves as the trigger's identifier.
•Check Content: Checks the optional HTTP header Content-MD5. This is a 128-bit "digest" used as a message integrity check. If the header has changed after the polling interval has passed, then the trigger fires. If the header is not provided by the server at the HTTP location, then the content is retrieved and hashed locally; the hashes are compared at subsequent polls.
•Check Modified Date: Checks the HTTP header Last-Modified. If the header is missing, the Content-MD5 header is checked (see above).
•Polling interval: Specifies the frequency, in seconds, with which the URI will be polled.
•Wait N seconds to settle: Defines the time in seconds that the server will wait before starting the next service.
•Start, Expires (optional): Defines, respectively, the start and end time of the period within which the service will run.
•Time zone: Specifies the timezone of the values in the Start and Expires fields.
•Enabled: This check box allows you to enable/disable the trigger.