Part of the NS1 Filter Chain™, health check filters eliminate answers that are currently down or experiencing higher traffic than the limits you define. There are two health check filters available for Filter Chain configuration: the Up and Shed Load filters.
This filter eliminates answers in which the "up" metadata value is false or 1, or if it is not set. In other words, it eliminates answers who are observed to be "down" (i.e., up=false). Typically, the "up" metadata field for an answer is connected to an NS1 monitor or third-party data source to enable automatic updates as network conditions change. Refer to Configuring automatic DNS failover for details.
If all answers are "up," this filter is bypassed and all answers are returned if all answers are eliminated as a result of the filter.
This filter eliminates answers in which the load is higher than the defined limits, resulting in slow or stopped traffic to high-traffic or overloaded endpoints. You must select a metric type — load average, average connections, or active requests — and then define low and high watermark values for that metric. This filter is used often to configure automatic load shedding where users create a data feed to automatically update load metrics within the answer metadata.
If the load metric value is below the specified low watermark, this filter does nothing. If the load value is between the low and high watermarks, the answer is eliminated some of the time — more often as it approaches the high watermark. If the load value is above the high watermark, the answer is eliminated completely.