allow configuring scanner cycles dynamically (#11931)

This allows us to speed up or slow down sleeps
between multiple scanner cycles, helps in testing
as well as some deployments might want to run
scanner more frequently.

This change is also dynamic can be applied on
a running cluster, subsequent cycles pickup
the newly set value.

cmd/config/scanner/scanner.go

@@ -1,5 +1,5 @@
 /*
- * MinIO Cloud Storage, (C) 2020 MinIO, Inc.
+ * MinIO Cloud Storage, (C) 2020-2021 MinIO, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -28,8 +28,10 @@ import (
 const (
 	Delay   = "delay"
 	MaxWait = "max_wait"
+	Cycle   = "cycle"
 
 	EnvDelay         = "MINIO_SCANNER_DELAY"
+	EnvCycle         = "MINIO_SCANNER_CYCLE"
 	EnvDelayLegacy   = "MINIO_CRAWLER_DELAY"
 	EnvMaxWait       = "MINIO_SCANNER_MAX_WAIT"
 	EnvMaxWaitLegacy = "MINIO_CRAWLER_MAX_WAIT"
@@ -41,6 +43,8 @@ type Config struct {
 	Delay float64 `json:"delay"`
 	// MaxWait is maximum wait time between operations
 	MaxWait time.Duration
+	// Cycle is the time.Duration between each scanner cycles
+	Cycle time.Duration
 }
 
 var (
@@ -54,6 +58,10 @@ var (
 			Key:   MaxWait,
 			Value: "15s",
 		},
+		config.KV{
+			Key:   Cycle,
+			Value: "1m",
+		},
 	}
 
 	// Help provides help for config values
@@ -70,6 +78,12 @@ var (
 			Optional:    true,
 			Type:        "duration",
 		},
+		config.HelpKV{
+			Key:         Cycle,
+			Description: `time duration between scanner cycles, defaults to '1m'`,
+			Optional:    true,
+			Type:        "duration",
+		},
 	}
 )
 
@@ -94,5 +108,10 @@ func LookupConfig(kvs config.KVS) (cfg Config, err error) {
 	if err != nil {
 		return cfg, err
 	}
+
+	cfg.Cycle, err = time.ParseDuration(env.Get(EnvCycle, kvs.Get(Cycle)))
+	if err != nil {
+		return cfg, err
+	}
 	return cfg, nil
 }