HTTP Triggers
An HTTP trigger enables you to monitor a URI (Uniform Resource Identifier) for changes. Specifically, you can poll the Last-Modified and Content-MD5 HTTP header fields for changes. You can configure the polling interval (e.g, every 60 seconds) and optionally set the start and expiry date of the trigger. The screenshot below illustrates a sample HTTP trigger.
The parameters of an HTTP trigger are described below.
Check | Specifies changes to track. The following options are available:
•HTTP Header Date instructs the system to check the Last-Modified HTTP header. If the Last-Modified HTTP header is missing, the Content-MD5 header is checked (see next option). •Content instructs the system to check the optional Content-MD5 HTTP header. This is a 128-bit hash value used as a message integrity check. If the MD5 header has changed after the polling interval has passed, the trigger fires. If the header is not provided by the server, the content is retrieved and hashed locally.
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Of URI | This is the URI you would like to check for changes.
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Polling interval | The frequency (in seconds) with which the URI will be polled.
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Wait N seconds for settle | If a change has been detected during the polling period, the server will wait for N seconds (the settle period) before checking the specified URI for further changes. If there have been no further changes during the settle period, the job will start. Otherwise, the server will wait again for the specified settle period and then check again if any changes have occurred since the last check.
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Start | Defines the trigger's start date and time. When you click in the date field, a pop-up calendar opens, which allows you to select the start date. You can also type in the date manually.
The value of the Time field must be in HH:MM:SS or HH:MM format.
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Expires | Defines the date and time when the trigger expires. When you click in the date field, a pop-up calendar opens, which allows you to select the expiry date. You can also type in the date manually.
The value of the Time field must be in HH:MM:SS or HH:MM format.
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Time zone | Defines the time zone of the start and expiry date and time. The default time zone is defined in the server administration settings.
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Priority (Advanced Edition) | In FlowForce Server Advanced Edition, you can assign priority to jobs in a queue. Priority is estimated based on all the jobs assigned to the queue. Priority can be low, below normal, normal, above normal, or high. The default priority is normal. You can set priority for any trigger type. If your job has multiple triggers configured, you can select different priority values for them, if necessary.
Global queues Setting trigger priority is particularly relevant to global queues, because you can decide which jobs are more important in a queue and should be fired first. In most cases, a job will have only one trigger. A job whose trigger has a higher priority and whose trigger conditions have been met will fire first.
Assuming there are several jobs in a global queue, and each job has several triggers of different priority, FlowForce will first check the triggers of higher priority. If the triggers' conditions are not fulfilled, FlowForce Server will then go on to check the triggers of lower priority. For a job with several triggers, it would make more sense to set the same priority value for all of them (e.g., high priority if the job is more important than others in the queue).
Local queues A local queue processes instances of one and the same job. If there is only one trigger configured, the priority value will be ignored. If there are several triggers of different priority, the triggers will compete with each other. For example, a job has a timer and a file-system trigger. The timer has a lower priority, whereas the file-system trigger has a higher priority. If the timer's condition has been fulfilled, and if there are no files to process, the timer will start the job earlier than the second trigger. However, if there are multiple files to process, the timer will wait, and the file-system trigger will be given priority.
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Enabled | The Enabled check box allows you to activate and deactivate the trigger.
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