Configuring an HTTP Watchdog


An HTTP Watchdog can be added to a Remote Host configuration in order to periodically poll the Remote Host to check its availability. The idea being that if the Remote Host becomes unavailable for some reason, a HTTP Interface can be brought down and will stop accepting requests. Once the Remote Host comes back online, the HTTP Interface will be automatically started up and will start accepting requests again.

To learn more about the reasons for shutting down an HTTP Interface if certain conditions do not hold, see Configuring Conditions for HTTP Interfaces.

To configure an HTTP Watchdog, right-click a previously configured Remote Host in the tree view of the Policy Studio and select th Watchdog -> Add menu option. Configure the following sections on the Configure HTTP Watchdog dialog.


Valid HTTP Response Code Ranges:

You can use this section to specify the HTTP response codes that you will regard as proof that the Remote Host is available. For example, if a 200 OK HTTP response is received for the poll request, the Remote Host can be considered available.

To specify a range of HTTP status codes, click the Add button and enter the Start and End of the range of HTTP response codes in the fields provided. An exact response code can be specified by entering the response code in both fields, e.g. "200".

HTTP Request for Polling:

The fields in this section allow you to configure the type and URI of the HTTP request to use to poll the Remote Host with. The default option is to use the Options HTTP command with a URI of "*", which is typically used to retrieve status information about the HTTP server. If you wish to use an alternative HTTP request to poll the Remote Host, select an HTTP request method from the Method, and specify the URI to use in the URI field.

Remote Host Polling:

The settings in this section determine when and how the HTTP Watchdog polls the Remote Host. The Poll Frequency determines how often the Watchdog is to send the polling request to the Remote Host.

By default, the Watchdog uses "real" HTTP requests to the Remote Host to determine its availability. In other words, if the API Gateway is sending a batch of requests to the Remote Host it will use the response codes from these requests to decide whether or not the Remote Host is up. Therefore, the Watchdog effectively "polls" the Remote Host by sending real HTTP requests to it.

If you want to configure the Watchdog to send poll requests during periods when it is not sending requests to and receiving responses from the Remote Host, you select Poll if up. In this case, the Watchdog uses real HTTP requests to poll the Remote Host as long as it sends them, but starts sending test poll requests when it is not sending HTTP requests to the Remote Host to test its availability.

[Important] Important

When a Remote Host is deemed to be down (an invalid HTTP response code was received) the Watchdog will continue to poll it at the configured Poll Frequency until it comes back up again (until a valid HTTP response code is received).