Go library to collect and emit metric and logging data from CF components.
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emitter Remove HttpStart and HttpStop Aug 24, 2016
factories Remove factories for HttpStart and HttpStop Aug 15, 2016
LICENSE Initial commit Mar 26, 2014
dropsonde.go Remove logger argument from `NewLogSender` Dec 23, 2016
dropsonde_suite_test.go Require verbose to view log output in tests Dec 27, 2016
dropsonde_test.go Renames autowiredEmitter to DefaultEmitter May 31, 2016



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Go library to collect and emit metric and logging data from CF components. https://godoc.org/github.com/cloudfoundry/dropsonde

Protocol Buffer format

See dropsonde-protocol for the full specification of the dropsonde Protocol Buffer format.

Use this script to generate Go handlers for the various protobuf messages.

Initialization and Configuration

import (

func main() {
    dropsonde.Initialize("localhost:3457", "router", "z1", "0")

This initializes dropsonde, along with the logs and metrics packages. It also instruments the default HTTP handler for outgoing requests, instrument itself (to count messages sent, etc.), and provides basic runtime stats.

The first argument is the destination for messages (typically metron). The host and port is required. The remaining arguments form the origin. This list is used by downstream portions of the dropsonde system to track the source of metrics.

Alternatively, import github.com/cloudfoundry/dropsonde/metrics to include the ability to send custom metrics, via metrics.SendValue and metrics.IncrementCounter.

Sending application logs and metrics

After calling dropsonde.Initialize (as above), the subpackages logs and metrics are also initialized. (They can be separately initialized, though this requires more setup of emitters, etc.)

Application Logs

Currently, dropsonde only supports sending logs for platform-hosted applications (i.e. not the emitting component itself).

Use logs.SendAppLog and logs.SendAppErrorLog to send single logs, e.g.

logs.SendAppLog("b7ba6142-6e6a-4e0b-81c1-d7025888cce4", "An event happened!", "APP", "0")

To process a stream of app logs (from, say, a socket of an application's STDOUT output), use logs.ScanLogStream and logs.ScanErrorLogStream:

logs.ScanLogStream("b7ba6142-6e6a-4e0b-81c1-d7025888cce4", "APP", "0", appLogSocketConnection)

See the Cloud Foundry DEA Logging Agent (currently deprecated) for an example code that scans log streams using these methods.


As mentioned earlier, initializing Dropsonde automatically instruments the default HTTP server and client objects in the net/http package, and will automatically send HttpStart and HttpStop events for every request served or made.

For instrumentation of other metrics, use the metrics package.

  • metrics.SendValue(name, value, unit) sends an event that records the value of a measurement at an instant in time. (These are often called "gauge" metrics by other libraries.) The value is of type float64, and the unit is mandatory. We recommend following this guide for unit names, and highly encourage SI units and prefixes where appropriate.
  • metrics.IncrementCounter(name) and metrics.AddToCounter(name, delta) send events that increment the named counter (by one or the specified non-negative delta, respectively). Note that the cumulative total is not included in the event message, only the increment.


There are some metric functions/methods which return Chainer types, which can be used to apply tags before sending. In the simplest case, the call will cascade until Send():

err := metrics.Value(name, value, unit).
    SetTag("foo", "bar").
    SetTag("bacon", 12).

In more complicated code, the chainer can be passed around, adding tags until the metric is ready to be sent. For example, pre-marshal, you may want to add tags about the type:

chainer := metrics.Value(name, value, unit).
    SetTag("req-mimetype", "json").
    SetTag("name", v.Name)

Later, it could tags about the chosen response type:

chainer = chainer.SetTag("resp-mimetype", respType)

And finally, add tags about the final state:

err := chainer.SetTag("resp-state", "error").
    SetTag("resp-code", http.StatusBadRequest).

Note: It is important to note that for counter metrics are summed individually and not in total. If you have historically emitted a counter without tags it is best practice to continue to emit that total metric without tags, and add additional metrics for the individual tagged metrics you'd like to track.

Manual usage

For details on manual usage of dropsonde, please refer to the Godocs. Pay particular attenion to the ByteEmitter, InstrumentedHandler, and InstrumentedRoundTripper types.

Handling dropsonde events

Programs wishing to emit events and metrics should use the package as described above. For programs that wish to process events, we provide the dropsonde/unmarshaller and dropsonde/marshaller packages for decoding/reencoding raw Protocol Buffer messages. Use dropsonde/signature to sign and validate messages.