Prometheus Scraper Support

Enabling Prometheus metrics

• In ddConfig table set [{dderl,dderl_prometheus,prometheusIsEnabled}] to true
• Configure basic auth in prometheus using [{dderl,dderl_prometheus,prometheusAuth}] in ddConfig table

Configuring metrics

• Metrics can be configured using [{dderl,dderl_prometheus,prometheusMetrics}] key in ddConfig. The default value is

  #{data_nodes => #{help => "Number of nodes in the cluster",labels => ["node","schema"],type => gauge},
    memory => #{help => "Memory",labels => ["node","schema"],type => gauge},
    port_count => #{help => "Number of Ports used",labels => ["node","schema"],type => gauge},
    process_count => #{help => "Process Count",labels => ["node","schema"],type => gauge},
    run_queue => #{help => "Run Queue Size",labels => ["node","schema"],type => gauge}}

• type should be one of guage, histogram, counter, summary orboolean
• help is a string or binary describing the metrics
• key is the name of the metric for example data_nodes
• labels(optional) correspond to the prometheus metric labels. Should be a list of string/binary
• buckets(optional) can be used with histogram and summary
• duration_unit(optional) can be used with summar

Configuring metrics fun

• This is the function that is being executed to fetch the mertics when the scraper is invoked

• Following is the default function. This can be changed by editing the value for key [{dderl,dderl_prometheus,prometheusMetricsFun}]

  fun (Config) ->
  #{data_nodes := DNodes} = imem_metrics:get_metric(data_nodes),
  #{port_count := Ports, process_count := Procs,
    erlang_memory := Memory, run_queue := RunQ} =
     imem_metrics:get_metric(system_information),
  Labels = [node(), imem_meta:schema()],
  maps:fold(fun (memory, _V, Acc) ->
     	  Acc#{memory => {Labels, Memory}};
           (process_count, _V, Acc) ->
     	  Acc#{process_count => {Labels, Procs}};
           (port_count, _V, Acc) ->
     	  Acc#{port_count => {Labels, 100}};
           (run_queue, _V, Acc) ->
     	  Acc#{run_queue => {Labels, RunQ}};
           (data_nodes, _V, Acc) ->
     	  Acc#{data_nodes => {Labels, length(DNodes)}};
           (K, V, Acc) -> Acc
        end, #{}, Config)
   end

- When using labels with a metrics expected result is a two tuple with first element a list a labels and then the value. The default function uses node and schema as labels.
- If not using labels in then the just the metrics value can be returned.