Excluded endpoints

Certain conditions may cause Envoy to exclude endpoints from load balancing. Excluding a host means that for any load balancing calculations that adjust weights based on the ratio of eligible hosts and total hosts (priority spillover, locality weighting and panic mode) Envoy will exclude these hosts in the denominator.

For example, with hosts in two priorities P0 and P1, where P0 looks like {healthy, unhealthy (excluded), unhealthy (excluded)} and where P1 looks like {healthy, healthy} all traffic will still hit P0, as 1 / (3 - 2) = 1.

Excluded hosts allow scaling up or down the number of hosts for a given cluster without entering panic mode or triggering priority spillover.

If panic mode is triggered, excluded hosts are still eligible for traffic; they simply do not contribute to the calculation when deciding whether panic mode is enabled or not.

Currently, the following two conditions can lead to a host being excluded when using active health checking:

• Using the ignore_new_hosts_until_first_hc cluster option.

• Receiving the x-envoy-immediate-health-check-fail header in a normal routed response or in response to an HTTP active health check.