BEAM Telemetry: Hackney Metrics
In the previous post of the series, I added basic metrics reporting to Cowboy, and simply wrote them to the logger. In this post, I’m going to do the same for the HTTP client, Hackney,.
The documentation for Hackney says that to enable metrics, you must add a
mod_metrics entry to its configuration. Let’s put together a small demo app and do that.
Hackney relies on erlang_metrics to abstract away the particular metrics
module you’re using. It includes support for exometer and folsom which are two popular metrics libraries in the
Erlang ecosystem,
The module that you specify in the configuration must implement certain functions.
erlang_metrics. The callback functions have changed a lot in the
newer version. Make sure you’re implementing the correct (older) ones.
-module(hackney_metrics_demo_metrics).
-export([new/2, delete/1, increment_counter/1, increment_counter/2, decrement_counter/1,
decrement_counter/2, update_histogram/2, update_gauge/2, update_meter/2]).
-include_lib("kernel/include/logger.hrl").
new(_Type, _Name) -> ok.
delete(_Name) -> ok.
increment_counter(Name) -> increment_counter(Name, 1).
increment_counter(Name, Value) -> ?LOG_INFO(#{f => ?FUNCTION_NAME, name => Name, value => Value}).
decrement_counter(Name) -> decrement_counter(Name, 1).
decrement_counter(Name, Value) -> ?LOG_INFO(#{f => ?FUNCTION_NAME, name => Name, value => Value}).
update_histogram(Name, Fun) when is_function(Fun, 0) ->
Begin = os:timestamp(),
Result = Fun(),
Duration = timer:now_diff(os:timestamp(), Begin) div 1000,
?LOG_INFO(#{f => ?FUNCTION_NAME, name => Name, value => Duration}),
Result;
update_histogram(Name, Value) when is_number(Value) ->
?LOG_INFO(#{f => ?FUNCTION_NAME, name => Name, value => Value}).
update_gauge(Name, Value) -> ?LOG_INFO(#{f => ?FUNCTION_NAME, name => Name, value => Value}).
update_meter(Name, Value) -> ?LOG_INFO(#{f => ?FUNCTION_NAME, name => Name, value => Value}).
If we make an HTTP request in the shell…
hackney:get(SomeUrl).
…we get a bunch of metrics:
f: increment_counter, name: [hackney,"blog.differentpla.net",nb_requests], value: 1
f: increment_counter, name: [hackney,nb_requests], value: 1
f: increment_counter, name: [hackney,total_requests], value: 1
f: update_histogram, name: [hackney_pool,default,in_use_count], value: 1
f: update_histogram, name: [hackney_pool,default,free_count], value: -1
f: update_histogram, name: [hackney,"blog.differentpla.net",connect_time], value: 77.395
f: increment_counter, name: [hackney_pool,"blog.differentpla.net",new_connection], value: 1
f: update_meter, name: [hackney_pool,default,take_rate], value: 1
f: increment_counter, name: [hackney_pool,"blog.differentpla.net",reuse_connection], value: 1
f: update_histogram, name: [hackney,"blog.differentpla.net",response_time], value: 130.577
I’d like to export these metrics to Prometheus. I’ll tackle that in a later post.