A dogstatsd client for Erlang

DogStatsD is Datadog's extension of StatsD. It adds tags to the metrics.

Configure

The defaults assume that you're running a statsd server on localhost (true if the agent is installed locally).

There are a number of configuration settings. You can either provide them as environment variables in ALL_CAPS or in an Erlang config file in all_lowercase.

| name               | type    | default       | info                                                                                  |
| ----               | ----    | -------       | ----                                                                                  |
| AGENT_ADDRESS      | string  | `"localhost"` | Hostname or IP where we can send the StatsD UDP packets                               |
| AGENT_PORT         | integer | `8125`        | Port that the StatsD agent is listening on                                            |
| GLOBAL_PREFIX      | string  | `""`          | Prefix to attach before all metric names. The `.` will be inserted for you            |
| GLOBAL_TAGS        | map     | `#{}`         | Tags to attach to all metrics                                                         |
| SEND_METRICS       | boolean | `true`        | Set to `false` when you're running tests to disable sending any metrics               |
| VM_STATS           | boolean | `true`        | Collect stats on the Erlang VM?                                                       |
| VM_STATS_DELAY     | integer | `60000`       | Time in ms between collection Erlang VM stats                                         |
| VM_STATS_SCHEDULER | boolean | `true`        | Collect stats on the scheduler?                                                       |
| VM_STATS_BASE_KEY  | string  | `"erlang.vm"` | All the VM stats will begin with this prefix (after the GLOBAL_PREFIX if that is set) |

Use

List dogstatsd in your rebar.config file

{deps, [
        {dogstatsd,     {git, "https://github.com/WhoopInc/dogstatsde.git"}}
]}.

List the dogstatsd application in your *.app.src file
Provide configuration as needed when starting up
For VM stats, no action is needed -- they'll collect on their own as long as the application is running
For custom metrics:

dogstatsd:gauge("users.active", UserCount, #{ shard => ShardId, version > Vsn })

VM Stats

If VM_STATS is not disabled, dogstatsd will periodically run erlang:statistics/1 and friends and collect data on the VM's performance:

name	erlang call	info
`proc_count`	`erlang:system_info(process_count)`
`proc_limit`	`erlang:system_info(process_limit)`
`messages_in_queues`	`process_info(Pid, message_queue_len)`	over all PIDs
`modules`	`length(code:all_loaded())`
`run_queue`	`erlang:statistics(run_queue)`
`error_logger_queue_len`	`process_info(Pid, message_queue_len)`	where `Pid` belongs to `error_logger`
`memory.total`	`erlang:memory()`
`memory.procs_userd`	`erlang:memory()`
`memory.atom_used`	`erlang:memory()`
`memory.binary`	`erlang:memory()`
`memory.ets`	`erlang:memory()`
`io.bytes_in`	`erlang:statistics(io)`
`io.bytes_out`	`erlang:statistics(io)`
`gc.count`	`erlang:statistics(garbage_collection)`
`gc.words_reclaimed`	`erlang:statistics(words_reclaimed)`
`reductions`	`erlang:statistics(reductions)`
`scheduler_wall_time.active`	`erlang:statistics(scheduler_wall_time)`	there are multiple schedulers, and the `scheduler` tag differentiates between them
`scheduler_wall_time.total`	`erlang:statistics(scheduler_wall_time)`	there are multiple schedulers, and the `scheduler` tag differentiates between them

screen-shot of VM stats in Datadog

Metric types

All metrics share the same signature:

-type metric_name() :: iodata().
-type metric_value() :: number().
-type metric_sample_rate() :: number().
-type metric_tags() :: map().

-spec MetricFunction(metric_name(), metric_value(), metric_sample_rate(), metric_tags()) -> ok.

The metric name is a string value with dots to separate levels of namespacing.
The sample rate is a number between [0.0,1.0]. This is the probability of sending a particular metric.
Tags are given as a map. The keys and values can be atoms, strings, or numbers.

Metric name and value are required. Sample rate defaults to 1.0. Tags defaults to an empty tag-set, but the value of GLOBAL_TAGS (which also defaults to an empty tag-set) is always merged with the passed tags.