add simulated latency (#583)

Signed-off-by: James Ranson <[email protected]>

docs/simulated-latency.md

@@ -0,0 +1,29 @@
+# Simulated Latency
+
+Trickster supports simulating latency on a per-backend basis, and can simulate both consistent and random durations of latency. Simulated latency is introduced in the frontend part of the proxy, and thus works with any backend provider.
+
+In `rule`, `alb` and other backend providers, where a request may transit multiple backend routes, only the Simulated Latency configs associated with the request entrypoint (first route) will be procssed, and not any subsequent routes the request is sent through.
+
+## Consistent Latency Duration
+
+In the Backend configuration, add a `latency_min_ms` value > 0, and the configured amount of latency will be introduced for each incoming request.
+
+## Random Latency
+
+ To simulate random latency, set `latency_max_ms` to a value > `latency_min_ms`, which may be 0 for random latency. Trickster will introduce a random amount of latency between (inclusive) the provided values.
+
+## Example Config
+
+```yaml
+frontend:
+  listen_port: 8480
+
+backends:
+  default:
+    origin_url: https://www.example.com
+    provider: reverseproxy
+    #
+    # introduce random latency between 50 and 150 milliseconds on each request
+    latency_min_ms: 50
+    latency_max_ms: 150
+```

examples/conf/example.full.yaml

@@ -358,6 +358,12 @@ backends:
 #     # default is 0
 #     shard_step_ms: 0
 
+#     # Simulated Latency
+#     # set latency_min_ms > 0 to apply a consistent latency to each request to this backend
+#     # set latency_max_ms > latency_max_ms (which can be 0) to apply a random latency between the two
+#     latency_max_ms = 0
+#     latency_max_ms = 0
+
 #     #
 #     # Each backend provider implements their own defaults for health checking
 #     # which can be overridden per backend configuration. See /docs/health.md for more information

pkg/backends/options/options.go

@@ -151,6 +151,16 @@ type Options struct {
 	// fronting backends that only support single range requests
 	DearticulateUpstreamRanges bool `yaml:"dearticulate_upstream_ranges,omitempty"`
 
+	// Simulated Latency
+	// When LatencyMinMS > 0 and LatencyMaxMS < LatencyMinMS (e.g., 0), then LatencyMinMS of latency
+	// are applied to the request. When LatencyMaxMS > LatencyMinMS, then a random amount of
+	// latency between the two values will be applied to the request
+	//
+	// LatencyMin is the minimum amount of simulated latency to apply to each incoming request
+	LatencyMinMS int `yaml:"latency_min_ms"`
+	// LatencyMax is the maximum amount of simulated latency to apply to each incoming request
+	LatencyMaxMS int `yaml:"latency_max_ms"`
+
 	// Synthesized Configurations
 	// These configurations are parsed versions of those defined above, and are what Trickster uses internally
 	//
@@ -263,6 +273,8 @@ func (o *Options) Clone() *Options {
 	no.FastForwardTTLMS = o.FastForwardTTLMS
 	no.ForwardedHeaders = o.ForwardedHeaders
 	no.Host = o.Host
+	no.LatencyMinMS = o.LatencyMinMS
+	no.LatencyMaxMS = o.LatencyMaxMS
 	no.Name = o.Name
 	no.IsDefault = o.IsDefault
 	no.KeepAliveTimeoutMS = o.KeepAliveTimeoutMS
@@ -360,9 +372,7 @@ func (l Lookup) Validate(ncl negative.Lookups) error {
 		if err != nil {
 			return err
 		}
-		if strings.HasSuffix(url.Path, "/") {
-			url.Path = url.Path[0 : len(url.Path)-1]
-		}
+		url.Path = strings.TrimSuffix(url.Path, "/")
 		o.Name = k
 		o.Scheme = url.Scheme
 		o.Host = url.Host
@@ -679,6 +689,14 @@ func SetDefaults(
 		no.Prometheus = o.Prometheus.Clone()
 	}
 
+	if metadata.IsDefined("backends", name, "latency_min_ms") {
+		no.LatencyMinMS = o.LatencyMinMS
+	}
+
+	if metadata.IsDefined("backends", name, "latency_max_ms") {
+		no.LatencyMaxMS = o.LatencyMaxMS
+	}
+
 	return no, nil
 }
 

pkg/util/middleware/config_context.go

@@ -17,7 +17,9 @@
 package middleware
 
 import (
+	"math/rand"
 	"net/http"
+	"time"
 
 	"github.com/trickstercache/trickster/v2/pkg/backends"
 	bo "github.com/trickstercache/trickster/v2/pkg/backends/options"
@@ -28,6 +30,10 @@ import (
 	"github.com/trickstercache/trickster/v2/pkg/proxy/request"
 )
 
+func init() {
+	rand.Seed(time.Now().UnixNano())
+}
+
 // WithResourcesContext ...
 func WithResourcesContext(client backends.Backend, o *bo.Options,
 	c cache.Cache, p *po.Options, t *tracing.Tracer,
@@ -46,6 +52,22 @@ func WithResourcesContext(client backends.Backend, o *bo.Options,
 			return
 		}
 		rsc.Merge(resources)
+
+		if o != nil && (o.LatencyMinMS > 0 || o.LatencyMaxMS > 0) {
+			processSimulatedLatency(o.LatencyMinMS, o.LatencyMaxMS)
+		}
+
 		next.ServeHTTP(w, r.WithContext(context.WithResources(r.Context(), rsc)))
 	})
 }
+
+func processSimulatedLatency(minMS, maxMS int) {
+	if (minMS == 0 && maxMS == 0) || (minMS < 0 || maxMS < 0) {
+		return
+	}
+	if minMS >= maxMS {
+		time.Sleep(time.Duration(minMS) * time.Millisecond)
+	}
+	diff := int64(maxMS - minMS)
+	time.Sleep(time.Duration((rand.Int63()%diff)+int64(minMS)) * time.Millisecond)
+}