Initial slow start support (#7810) (#7905)

* Initial slow start support (#7810)

* Initial slow start support

* Add changelog

* Update changelog

* Update changelog version

* Update changelog version

* Update changelog version

---------

Co-authored-by: Nathan Fudenberg <[email protected]>

* ci

* changelog: Backport requires downgrade of type

---------

Co-authored-by: Nick Caballero <[email protected]>
Co-authored-by: soloio-bulldozer[bot] <48420018+soloio-bulldozer[bot]@users.noreply.github.com>

changelog/v1.13.9/envoy-slow-start-config.yaml

@@ -0,0 +1,4 @@
+changelog:
+  - type: FIX
+    issueLink: https://github.com/solo-io/gloo/issues/7807
+    description: Expose `config.core.v3.Cluster.SlowStartConfig` for `RoundRobin` and `LeastRequest` load balancers. Requires CRD update to be able to use.

install/helm/gloo/crds/gloo.solo.io_v1_Upstream.yaml

@@ -884,6 +884,17 @@ spec:
                       choiceCount:
                         format: int32
                         type: integer
+                      slowStartConfig:
+                        properties:
+                          aggression:
+                            nullable: true
+                            type: number
+                          minWeightPercent:
+                            nullable: true
+                            type: number
+                          slowStartWindow:
+                            type: string
+                        type: object
                     type: object
                   localityWeightedLbConfig:
                     maxProperties: 0
@@ -907,6 +918,18 @@ spec:
                         type: object
                     type: object
                   roundRobin:
+                    properties:
+                      slowStartConfig:
+                        properties:
+                          aggression:
+                            nullable: true
+                            type: number
+                          minWeightPercent:
+                            nullable: true
+                            type: number
+                          slowStartWindow:
+                            type: string
+                        type: object
                     type: object
                   updateMergeWindow:
                     type: string

projects/gloo/api/v1/load_balancer.proto

@@ -25,10 +25,16 @@ message LoadBalancerConfig {
     // Set to 0 to disable and have changes applied immediately.
     google.protobuf.Duration update_merge_window = 2;
 
-    message RoundRobin {}
+    message RoundRobin {
+        // Configuration for slow start mode. If this configuration is not set, slow start will not be not enabled.
+        SlowStartConfig slow_start_config = 1;
+    }
     message LeastRequest {
         // How many choices to take into account. defaults to 2.
         uint32 choice_count = 1;
+
+        // Configuration for slow start mode. If this configuration is not set, slow start will not be not enabled.
+        SlowStartConfig slow_start_config = 2;
     }
     message Random {}
 
@@ -72,4 +78,29 @@ message LoadBalancerConfig {
         google.protobuf.Empty locality_weighted_lb_config = 8;
     }
 
+    message SlowStartConfig {
+        // Represents the size of slow start window.
+        // If set, the newly created host remains in slow start mode starting from its creation time
+        // for the duration of slow start window.
+        google.protobuf.Duration slow_start_window = 1;
+
+        // This parameter controls the speed of traffic increase over the slow start window. Defaults to 1.0,
+        // so that endpoint would get linearly increasing amount of traffic.
+        // When increasing the value for this parameter, the speed of traffic ramp-up increases non-linearly.
+        // The value of aggression parameter should be greater than 0.0.
+        // By tuning the parameter, is possible to achieve polynomial or exponential shape of ramp-up curve.
+        //
+        // During slow start window, effective weight of an endpoint would be scaled with time factor and aggression:
+        // ``new_weight = weight * max(min_weight_percent, time_factor ^ (1 / aggression))``,
+        // where ``time_factor=(time_since_start_seconds / slow_start_time_seconds)``.
+        //
+        // As time progresses, more and more traffic would be sent to endpoint, which is in slow start window.
+        // Once host exits slow start, time_factor and aggression no longer affect its weight.
+        google.protobuf.DoubleValue aggression = 2;
+
+        // Configures the minimum percentage of origin weight that avoids too small new weight,
+        // which may cause endpoints in slow start mode receive no traffic in slow start window.
+        // If not specified, the default is 10%.
+        google.protobuf.DoubleValue min_weight_percent = 3;
+    }
 }