Add note about motivation to docs

Signed-off-by: James Forcier <jforcier@grubhub.com>
envoyproxy · Aug 27, 2019 · 5a93215 · 5a93215
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diff --git a/api/envoy/api/v2/cds.proto b/api/envoy/api/v2/cds.proto
@@ -541,7 +541,8 @@ message Cluster {
       google.protobuf.UInt64Value min_cluster_size = 2;
 
       // If set to true, Envoy will not consider any hosts when the cluster is in panic mode.
-      // Instead, the cluster will fail all requests as if all hosts are unhealthy.
+      // Instead, the cluster will fail all requests as if all hosts are unhealthy. This can help
+      // avoid potentially overwhelming a failing service.
       bool fail_traffic_on_panic = 3;
     }
     // Configuration for :ref:`locality weighted load balancing

diff --git a/docs/root/intro/arch_overview/upstream/load_balancing/panic_threshold.rst b/docs/root/intro/arch_overview/upstream/load_balancing/panic_threshold.rst
@@ -15,6 +15,8 @@ cluster as load increases.
 There are two modes Envoy can choose from when in a panic state: traffic will either be sent to all
 hosts, or will be sent to no hosts (and therefore will always fail). This is configured in the
 :ref:`cluster configuration <envoy_api_field_Cluster.CommonLbConfig.ZoneAwareLbConfig.fail_traffic_on_panic>`.
+Choosing to fail traffic during panic scenarios can help avoid overwhelming potentially failing
+upstream services.
 
 Panic thresholds work in conjunction with priorities. If the number of available hosts in a given
 priority goes down, Envoy will try to shift some traffic to lower priorities. If it succeeds in