metrics: return histograms for time metrics

command/src/command.proto

@@ -574,6 +574,7 @@ message FilteredMetrics {
         uint64 time = 3;
         Percentiles percentiles = 4;
         FilteredTimeSerie time_serie = 5;
+        FilteredHistogram histogram = 6;
     }
 }
 
@@ -583,7 +584,6 @@ message FilteredTimeSerie {
     repeated uint32 last_hour = 3;
 }
 
-
 message Percentiles {
     required uint64 samples = 1;
     required uint64 p_50 = 2;
@@ -595,6 +595,20 @@ message Percentiles {
     required uint64 p_100 = 8;
 }
 
+// a histogram meant to be translated to prometheus
+message FilteredHistogram {
+    required uint64 sum = 1;
+    required uint64 count = 2;
+    repeated Bucket buckets = 3;
+}
+
+// a prometheus histogram bucket
+message Bucket {
+    required uint64 count = 1;
+    // upper range of the bucket (le = less or equal)
+    required uint64 le = 2;
+}
+
 message RequestCounts {
     map<string, int32> map = 1;
-}
+}

lib/src/metrics/local_drain.rs

@@ -8,14 +8,14 @@ use std::{
 use hdrhistogram::Histogram;
 
 use sozu_command::proto::command::{
-    filtered_metrics, response_content::ContentType, AvailableMetrics, BackendMetrics,
-    ClusterMetrics, FilteredMetrics, MetricsConfiguration, Percentiles, QueryMetricsOptions,
-    ResponseContent, WorkerMetrics,
+    filtered_metrics, response_content::ContentType, AvailableMetrics, BackendMetrics, Bucket,
+    ClusterMetrics, FilteredHistogram, FilteredMetrics, MetricsConfiguration, Percentiles,
+    QueryMetricsOptions, ResponseContent, WorkerMetrics,
 };
 
 use crate::metrics::{MetricError, MetricValue, Subscriber};
 
-/// This is how the metrics are stored in the local drain
+/// metrics as stored in the local drain
 #[derive(Debug, Clone)]
 pub enum AggregatedMetric {
     Gauge(usize),
@@ -88,6 +88,30 @@ impl AggregatedMetric {
     }
 }
 
+/// filter "inside" metrics by names, turn them into sendable ones
+fn filter_aggregated_metrics(
+    aggregated: &BTreeMap<String, AggregatedMetric>,
+    metric_names: &Vec<String>,
+) -> BTreeMap<String, FilteredMetrics> {
+    let mut to_filter = aggregated.clone();
+    if !metric_names.is_empty() {
+        to_filter.retain(|key, _| metric_names.contains(key));
+    }
+
+    let mut filtered_metrics = BTreeMap::new();
+    for (name, metric) in to_filter {
+        filtered_metrics.insert(name.to_owned(), metric.to_filtered());
+        // convert time metrics to a histogram format, on top of percentiles
+        match metric {
+            AggregatedMetric::Time(ref hist) => {
+                filtered_metrics.insert(format!("{}_hist", name), filter_histogram(hist));
+            }
+            _ => {}
+        }
+    }
+    filtered_metrics
+}
+
 pub fn histogram_to_percentiles(hist: &Histogram<u32>) -> Percentiles {
     Percentiles {
         samples: hist.len(),
@@ -101,6 +125,30 @@ pub fn histogram_to_percentiles(hist: &Histogram<u32>) -> Percentiles {
     }
 }
 
+pub fn filter_histogram(hist: &Histogram<u32>) -> FilteredMetrics {
+    let count = hist.len();
+    let mean = hist.mean();
+    let min = hist.min();
+    let max = hist.max();
+    let sum = (count as f64 * mean) as u64;
+    let range = max - min;
+    let number_of_buckets = 10;
+    let mut buckets = Vec::new();
+
+    for i in 0..number_of_buckets {
+        let le = min + (i * range) / number_of_buckets;
+        let count = hist.count_between(min, min + le);
+        buckets.push(Bucket { le, count });
+    }
+    FilteredMetrics {
+        inner: Some(filtered_metrics::Inner::Histogram(FilteredHistogram {
+            sum,
+            count,
+            buckets,
+        })),
+    }
+}
+
 #[derive(Copy, Clone, Debug, PartialEq)]
 enum MetricKind {
     Gauge,
@@ -306,17 +354,7 @@ impl LocalDrain {
         &mut self,
         metric_names: &Vec<String>,
     ) -> BTreeMap<String, FilteredMetrics> {
-        self.proxy_metrics
-            .iter()
-            .filter(|(key, _)| {
-                if metric_names.is_empty() {
-                    true
-                } else {
-                    metric_names.contains(key)
-                }
-            })
-            .map(|(key, value)| (key.to_string(), value.to_filtered()))
-            .collect()
+        filter_aggregated_metrics(&self.proxy_metrics, metric_names)
     }
 
     pub fn dump_cluster_metrics(