Crate metrics_cloudwatch_embedded

Backend for the metrics crate to emit metrics in the CloudWatch Embedded Metrics Format (https://docs.aws.amazon.com/AmazonCloudWatch/latest/monitoring/CloudWatch_Embedded_Metric_Format_Specification.html)

Counters, Gauges and Histograms are supported.

Example

let metrics = metrics_cloudwatch_embedded::Builder::new()
     .cloudwatch_namespace("MyApplication")
     .init()
     .unwrap();

 metrics::counter!("requests", "Method" => "Default").increment(1);

 metrics
     .set_property("RequestId", "ABC123")
     .flush(std::io::stdout());

Implementation Details

Intended for use with the lambda_runtime, however Collector::flush(…) could be used for anything that writes logs that end up in CloudWatch.

• Counters are Guages are implented as AtomicU64 via the CounterFn and GaugeFn implementations in the metrics crate
• Histograms are implemented as mpsc::SyncSender
• serde_json is used to serialize metric documents to simplify maintainence and for consistancy with other crates in the ecosystem
• Registering and flushing of metrics uses state within a Mutex, recording previously registered metrics should not block on this Mutex
• Metric names are mapped to metrics::Unit regardless of their type and labels
• Metric descriptions are unused

Limitations

• Histograms retain up to 100 values (the maximum for a single metric document) between calls to Collector::flush(), overflow will report an error via the tracing crate
• Dimensions set at initialization via Builder::with_dimension(…) may not overlap with metric labels
• Only the subset of metric units in metrics::Unit are supported https://docs.aws.amazon.com/AmazonCloudWatch/latest/APIReference/API_MetricDatum.html
• Registering different metric types with the same metrics::Key will fail with an error via the tracing crate
• The Embedded Metric Format supports a maximum of 30 dimensions per metric, attempting to register a metric with more than 30 dimensions/labels will fail with an error via the tracing crate

Modules

• lambda
  Additional functionality for integration with lambda_runtime and lambda_http

Structs

• Builder
  Builder for the Embedded Cloudwatch Metrics Collector
• Collector
  Embedded CloudWatch Metrics Collector + Emitter