Move CloudWatch rate limit to config (#1673)

* Move CloudWatch rate limit to config
Reference #1670

* make that variable a string

* ahem, apparently limiter wants an int

* add the ratelimit to the sample config

* update the test to include the rate

* set a default value of 10 for ratelimit

* Move default ratelimit to init

plugins/inputs/cloudwatch/README.md

@@ -34,6 +34,11 @@ API endpoint. In the following order the plugin will attempt to authenticate.
   ## Metric Statistic Namespace (required)
   namespace = 'AWS/ELB'
 
+  ## Maximum requests per second. Note that the global default AWS rate limit is
+  ## 10 reqs/sec, so if you define multiple namespaces, these should add up to a
+  ## maximum of 10. Optional - default value is 10.
+  ratelimit = 10
+
   ## Metrics to Pull (optional)
   ## Defaults to all Metrics in Namespace if nothing is provided
   ## Refreshes Namespace available metrics every 1h

plugins/inputs/cloudwatch/cloudwatch.go

@@ -33,6 +33,7 @@ type (
 		Namespace   string            `toml:"namespace"`
 		Metrics     []*Metric         `toml:"metrics"`
 		CacheTTL    internal.Duration `toml:"cache_ttl"`
+		RateLimit   int               `toml:"ratelimit"`
 		client      cloudwatchClient
 		metricCache *MetricCache
 	}
@@ -96,6 +97,11 @@ func (c *CloudWatch) SampleConfig() string {
   ## Metric Statistic Namespace (required)
   namespace = 'AWS/ELB'
 
+  ## Maximum requests per second. Note that the global default AWS rate limit is
+  ## 10 reqs/sec, so if you define multiple namespaces, these should add up to a
+  ## maximum of 10. Optional - default value is 10.
+  ratelimit = 10
+
   ## Metrics to Pull (optional)
   ## Defaults to all Metrics in Namespace if nothing is provided
   ## Refreshes Namespace available metrics every 1h
@@ -175,7 +181,7 @@ func (c *CloudWatch) Gather(acc telegraf.Accumulator) error {
 	// limit concurrency or we can easily exhaust user connection limit
 	// see cloudwatch API request limits:
 	// http://docs.aws.amazon.com/AmazonCloudWatch/latest/DeveloperGuide/cloudwatch_limits.html
-	lmtr := limiter.NewRateLimiter(10, time.Second)
+	lmtr := limiter.NewRateLimiter(c.RateLimit, time.Second)
 	defer lmtr.Stop()
 	var wg sync.WaitGroup
 	wg.Add(len(metrics))
@@ -196,6 +202,7 @@ func init() {
 		ttl, _ := time.ParseDuration("1hr")
 		return &CloudWatch{
 			CacheTTL:  internal.Duration{Duration: ttl},
+			RateLimit: 10,
 		}
 	})
 }

plugins/inputs/cloudwatch/cloudwatch_test.go

@@ -58,6 +58,7 @@ func TestGather(t *testing.T) {
 		Namespace: "AWS/ELB",
 		Delay:     internalDuration,
 		Period:    internalDuration,
+		RateLimit: 10,
 	}
 
 	var acc testutil.Accumulator