Add CloudWatch input plugin

Rebased commit of previously reviewed branch.
Added cloudwatch client Mock and more rich unit tests.

closes #935
closes #936

CHANGELOG.md

@@ -3,6 +3,7 @@
 ### Features
 - [#976](https://github.com/influxdata/telegraf/pull/976): Reduce allocations in the UDP and statsd inputs.
 - [#979](https://github.com/influxdata/telegraf/pull/979): Reduce allocations in the TCP listener.
+- [#935](https://github.com/influxdata/telegraf/pull/935): AWS Cloudwatch input plugin. Thanks @joshhardy & @ljosa!
 
 ### Bugfixes
 - [#968](https://github.com/influxdata/telegraf/issues/968): Processes plugin gets unknown state when spaces are in (command name)

plugins/inputs/all/all.go

@@ -4,6 +4,7 @@ import (
 	_ "github.com/influxdata/telegraf/plugins/inputs/aerospike"
 	_ "github.com/influxdata/telegraf/plugins/inputs/apache"
 	_ "github.com/influxdata/telegraf/plugins/inputs/bcache"
+	_ "github.com/influxdata/telegraf/plugins/inputs/cloudwatch"
 	_ "github.com/influxdata/telegraf/plugins/inputs/couchbase"
 	_ "github.com/influxdata/telegraf/plugins/inputs/couchdb"
 	_ "github.com/influxdata/telegraf/plugins/inputs/disque"

plugins/inputs/cloudwatch/README.md

@@ -0,0 +1,86 @@
+# Amazon CloudWatch Statistics Input
+
+This plugin will pull Metric Statistics from Amazon CloudWatch.
+
+### Amazon Authentication
+
+This plugin uses a credential chain for Authentication with the CloudWatch
+API endpoint. In the following order the plugin will attempt to authenticate.
+1. [IAMS Role](http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/iam-roles-for-amazon-ec2.html)
+2. [Environment Variables](https://github.com/aws/aws-sdk-go/wiki/configuring-sdk#environment-variables)
+3. [Shared Credentials](https://github.com/aws/aws-sdk-go/wiki/configuring-sdk#shared-credentials-file)
+
+### Configuration:
+
+```toml
+[[inputs.cloudwatch]]
+  ## Amazon Region (required)
+  region = 'us-east-1'
+
+  ## Requested CloudWatch aggregation Period (required - must be a multiple of 60s)
+  period = '1m'
+
+  ## Collection Delay (required - must account for metrics availability via CloudWatch API)
+  delay = '1m'
+
+  ## Override global run interval (optional - defaults to global interval)
+  ## Recomended: use metric 'interval' that is a multiple of 'period' to avoid 
+  ## gaps or overlap in pulled data
+  interval = '1m'
+
+  ## Metric Statistic Namespace (required)
+  namespace = 'AWS/ELB'
+
+  ## Metrics to Pull (optional)
+  ## Defaults to all Metrics in Namespace if nothing is provided
+  ## Refreshes Namespace available metrics every 1h
+  [[inputs.cloudwatch.metrics]]
+    names = ['Latency', 'RequestCount']
+
+    ## Dimension filters for Metric (optional)
+    [[inputs.cloudwatch.metrics.dimensions]]
+      name = 'LoadBalancerName'
+      value = 'p-example'
+```
+#### Requirements and Terminology
+
+Plugin Configuration utilizes [CloudWatch concepts](http://docs.aws.amazon.com/AmazonCloudWatch/latest/DeveloperGuide/cloudwatch_concepts.html) and access pattern to allow monitoring of any CloudWatch Metric.
+
+- `region` must be a valid AWS [Region](http://docs.aws.amazon.com/AmazonCloudWatch/latest/DeveloperGuide/cloudwatch_concepts.html#CloudWatchRegions) value
+- `period` must be a valid CloudWatch [Period](http://docs.aws.amazon.com/AmazonCloudWatch/latest/DeveloperGuide/cloudwatch_concepts.html#CloudWatchPeriods) value
+- `namespace` must be a valid CloudWatch [Namespace](http://docs.aws.amazon.com/AmazonCloudWatch/latest/DeveloperGuide/cloudwatch_concepts.html#Namespace) value
+- `names` must be valid CloudWatch [Metric](http://docs.aws.amazon.com/AmazonCloudWatch/latest/DeveloperGuide/cloudwatch_concepts.html#Metric) names
+- `dimensions` must be valid CloudWatch [Dimension](http://docs.aws.amazon.com/AmazonCloudWatch/latest/DeveloperGuide/cloudwatch_concepts.html#Dimension) name/value pairs
+
+#### Restrictions and Limitations
+- CloudWatch metrics are not available instantly via the CloudWatch API. You should adjust your collection `delay` to account for this lag in metrics availability based on your [monitoring subscription level](http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/using-cloudwatch-new.html)
+- CloudWatch API usage incurs cost - see [GetMetricStatistics Pricing](https://aws.amazon.com/cloudwatch/pricing/)
+
+### Measurements & Fields:
+
+Each CloudWatch Namespace monitored records a measurement with fields for each available Metric Statistic
+Namespace and Metrics are represented in [snake case](https://en.wikipedia.org/wiki/Snake_case)
+
+- cloudwatch_{namespace}
+  - {metric}_sum         (metric Sum value)
+  - {metric}_average     (metric Average value)
+  - {metric}_minimum     (metric Minimum value)
+  - {metric}_maximum     (metric Maximum value)
+  - {metric}_sample_count (metric SampleCount value)
+
+
+### Tags:
+Each measurement is tagged with the following identifiers to uniquely identify the associated metric
+Tag Dimension names are represented in [snake case](https://en.wikipedia.org/wiki/Snake_case)
+
+- All measurements have the following tags:
+  - region           (CloudWatch Region)
+  - unit             (CloudWatch Metric Unit)
+  - {dimension-name} (Cloudwatch Dimension value - one for each metric dimension)
+
+### Example Output:
+
+```
+$ ./telegraf -config telegraf.conf -input-filter cloudwatch -test
+> cloudwatch_aws_elb,load_balancer_name=p-example,region=us-east-1,unit=seconds latency_average=0.004810798017284538,latency_maximum=0.1100282669067383,latency_minimum=0.0006084442138671875,latency_sample_count=4029,latency_sum=19.382705211639404 1459542420000000000
+```