proxy: move metrics::prometheus module to root metrics module (#763)

The proxy `telemetry::metrics::prometheus` module was initially added in order to give the Prometheus metrics export code a separate namespace from the controller push metrics. Since the controller push metrics code was removed from the proxy in #616, we no longer need a separate module for the Prometheus-specific metrics code. Therefore, I've moved that code to the root `telemetry::metrics` module, which should hopefully make the proxy source tree structure a little simpler.

This is a fairly trivial refactor.

Signed-off-by: Eliza Weisman <eliza@buoyant.io>

proxy/src/control/discovery.rs

@@ -30,7 +30,7 @@ use transport::DnsNameAndPort;
 
 use control::cache::{Cache, CacheChange, Exists};
 
-use ::telemetry::metrics::prometheus::{DstLabels, Labeled};
+use ::telemetry::metrics::{DstLabels, Labeled};
 
 /// A handle to start watching a destination for address changes.
 #[derive(Clone, Debug)]

proxy/src/ctx/http.rs

@@ -2,7 +2,7 @@ use http;
 use std::sync::Arc;
 
 use ctx;
-use telemetry::metrics::prometheus;
+use telemetry::metrics;
 
 /// Describes a stream's request headers.
 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
@@ -22,7 +22,7 @@ pub struct Request {
     /// Optional information on the request's destination service, which may
     /// be provided by the control plane for destinations lookups against its
     /// discovery API.
-    pub dst_labels: Option<prometheus::DstLabels>,
+    pub dst_labels: Option<metrics::DstLabels>,
 }
 
 /// Describes a stream's response headers.
@@ -51,7 +51,7 @@ impl Request {
         // destination labels from the control plane's discovery API.
         let dst_labels = request
             .extensions()
-            .get::<prometheus::DstLabels>()
+            .get::<metrics::DstLabels>()
             .cloned();
         let r = Self {
             id,

proxy/src/outbound.rs

@@ -18,7 +18,7 @@ use bind::{self, Bind, Protocol};
 use control::{self, discovery};
 use control::discovery::Bind as BindTrait;
 use ctx;
-use telemetry::metrics::prometheus;
+use telemetry::metrics;
 use timeout::Timeout;
 use transparency::h1;
 use transport::{DnsNameAndPort, Host, HostAndPort};
@@ -170,7 +170,7 @@ where
     type Request = http::Request<B>;
     type Response = bind::HttpResponse;
     type Error = <Self::Service as tower::Service>::Error;
-    type Service = prometheus::Labeled<bind::Service<B>>;
+    type Service = metrics::Labeled<bind::Service<B>>;
     type DiscoverError = BindError;
 
     fn poll(&mut self) -> Poll<Change<Self::Key, Self::Service>, Self::DiscoverError> {
@@ -187,7 +187,7 @@ where
                     let svc = bind.bind(&addr)
                         // The controller has no labels to add to an external
                         // service.
-                        .map(prometheus::Labeled::none)
+                        .map(metrics::Labeled::none)
                         .map_err(|_| BindError::External{ addr })?;
                     Ok(Async::Ready(Change::Insert(addr, svc)))
                 } else {

proxy/src/telemetry/control.rs

@@ -6,7 +6,7 @@ use futures_mpsc_lossy::Receiver;
 use tokio_core::reactor::Handle;
 
 use super::event::Event;
-use super::metrics::prometheus;
+use super::metrics;
 use super::tap::Taps;
 use connection;
 use ctx;
@@ -34,10 +34,10 @@ pub struct MakeControl {
 #[derive(Debug)]
 pub struct Control {
     /// Aggregates scrapable metrics.
-    metrics_aggregate: prometheus::Aggregate,
+    metrics_aggregate: metrics::Aggregate,
 
     /// Serves scrapable metrics.
-    metrics_service: prometheus::Serve,
+    metrics_service: metrics::Serve,
 
     /// Receives telemetry events.
     rx: Option<Receiver<Event>>,
@@ -77,7 +77,7 @@ impl MakeControl {
     /// - `Err(io::Error)` if the timeout could not be created.
     pub fn make_control(self, taps: &Arc<Mutex<Taps>>, handle: &Handle) -> io::Result<Control> {
         let (metrics_aggregate, metrics_service) =
-            prometheus::new(&self.process_ctx);
+            metrics::new(&self.process_ctx);
 
         Ok(Control {
             metrics_aggregate,

proxy/src/telemetry/metrics/latency.rs

@@ -2,8 +2,7 @@
 use std::{fmt, iter, ops, slice, u32};
 use std::num::Wrapping;
 use std::time::Duration;
-
-use super::prometheus;
+use super::Counter;
 
 /// The number of buckets in a  latency histogram.
 pub const NUM_BUCKETS: usize = 26;
@@ -64,7 +63,7 @@ pub struct Histogram {
     /// Array of buckets in which to count latencies.
     ///
     /// The upper bound of a given bucket `i` is given in `BUCKET_BOUNDS[i]`.
-    buckets: [prometheus::Counter; NUM_BUCKETS],
+    buckets: [Counter; NUM_BUCKETS],
 
     /// The total sum of all observed latency values.
     ///
@@ -137,8 +136,8 @@ where
 impl<'a> IntoIterator for &'a Histogram {
     type Item = u64;
     type IntoIter = iter::Map<
-        slice::Iter<'a, prometheus::Counter>,
-        fn(&'a prometheus::Counter) -> u64
+        slice::Iter<'a, Counter>,
+        fn(&'a Counter) -> u64
     >;
 
     fn into_iter(self) -> Self::IntoIter {

proxy/src/telemetry/metrics/mod.rs

@@ -1,2 +1,455 @@
+//! Aggregates and serves Prometheus metrics.
+//!
+//! # A note on label formatting
+//!
+//! Prometheus labels are represented as a comma-separated list of values
+//! Since the Conduit proxy labels its metrics with a fixed set of labels
+//! which we know in advance, we represent these labels using a number of
+//! `struct`s, all of which implement `fmt::Display`. Some of the label
+//! `struct`s contain other structs which represent a subset of the labels
+//! which can be present on metrics in that scope. In this case, the
+//! `fmt::Display` impls for those structs call the `fmt::Display` impls for
+//! the structs that they own. This has the potential to complicate the
+//! insertion of commas to separate label values.
+//!
+//! In order to ensure that commas are added correctly to separate labels,
+//! we expect the `fmt::Display` implementations for label types to behave in
+//! a consistent way: A label struct is *never* responsible for printing
+//! leading or trailing commas before or after the label values it contains.
+//! If it contains multiple labels, it *is* responsible for ensuring any
+//! labels it owns are comma-separated. This way, the `fmt::Display` impl for
+//! any struct that represents a subset of the labels are position-agnostic;
+//! they don't need to know if there are other labels before or after them in
+//! the formatted output. The owner is responsible for managing that.
+//!
+//! If this rule is followed consistently across all structs representing
+//! labels, we can add new labels or modify the existing ones without having
+//! to worry about missing commas, double commas, or trailing commas at the
+//! end of the label set (all of which will make Prometheus angry).
+use std::default::Default;
+use std::{fmt, ops, time};
+use std::hash::Hash;
+use std::num::Wrapping;
+use std::sync::{Arc, Mutex};
+
+use futures::future::{self, FutureResult};
+use hyper;
+use hyper::header::{ContentLength, ContentType};
+use hyper::StatusCode;
+use hyper::server::{
+    Service as HyperService,
+    Request as HyperRequest,
+    Response as HyperResponse
+};
+use indexmap::{IndexMap};
+
+use ctx;
+use telemetry::event::Event;
+
+mod labels;
 mod latency;
-pub mod prometheus;
+
+use self::labels::{RequestLabels, ResponseLabels};
+use self::latency::{BUCKET_BOUNDS, Histogram};
+pub use self::labels::{DstLabels, Labeled};
+
+#[derive(Debug, Clone)]
+struct Metrics {
+    request_total: Metric<Counter, Arc<RequestLabels>>,
+    request_duration: Metric<Histogram, Arc<RequestLabels>>,
+
+    response_total: Metric<Counter, Arc<ResponseLabels>>,
+    response_duration: Metric<Histogram, Arc<ResponseLabels>>,
+    response_latency: Metric<Histogram, Arc<ResponseLabels>>,
+
+    start_time: u64,
+}
+
+#[derive(Debug, Clone)]
+struct Metric<M, L: Hash + Eq> {
+    name: &'static str,
+    help: &'static str,
+    values: IndexMap<L, M>
+}
+
+/// A Prometheus counter is represented by a `Wrapping` unsigned 64-bit int.
+///
+/// Counters always explicitly wrap on overflows rather than panicking in
+/// debug builds. Prometheus' [`rate()`] and [`irate()`] queries handle breaks
+/// in monotonicity gracefully  (see also [`resets()`]), so wrapping is less
+/// problematic than panicking in this case.
+///
+/// Note, however, that Prometheus represents counters using 64-bit
+/// floating-point numbers. The correct semantics are to ensure the counter
+/// always gets reset to zero after Prometheus reads it, before it would ever
+/// overflow a 52-bit `f64` mantissa.
+///
+/// [`rate()`]: https://prometheus.io/docs/prometheus/latest/querying/functions/#rate()
+/// [`irate()`]: https://prometheus.io/docs/prometheus/latest/querying/functions/#irate()
+/// [`resets()`]: https://prometheus.io/docs/prometheus/latest/querying/functions/#resets
+///
+// TODO: Implement Prometheus reset semantics correctly, taking into
+//       consideration that Prometheus models counters as `f64` and so
+//       there are only 52 significant bits.
+#[derive(Copy, Debug, Default, Clone, Eq, PartialEq)]
+pub struct Counter(Wrapping<u64>);
+
+/// Tracks Prometheus metrics
+#[derive(Debug)]
+pub struct Aggregate {
+    metrics: Arc<Mutex<Metrics>>,
+}
+
+/// Serve Prometheues metrics.
+#[derive(Debug, Clone)]
+pub struct Serve {
+    metrics: Arc<Mutex<Metrics>>,
+}
+
+/// Construct the Prometheus metrics.
+///
+/// Returns the `Aggregate` and `Serve` sides. The `Serve` side
+/// is a Hyper service which can be used to create the server for the
+/// scrape endpoint, while the `Aggregate` side can receive updates to the
+/// metrics by calling `record_event`.
+pub fn new(process: &Arc<ctx::Process>) -> (Aggregate, Serve) {
+    let metrics = Arc::new(Mutex::new(Metrics::new(process)));
+    (Aggregate::new(&metrics), Serve::new(&metrics))
+}
+
+// ===== impl Metrics =====
+
+impl Metrics {
+
+    pub fn new(process: &Arc<ctx::Process>) -> Self {
+
+        let start_time = process.start_time
+            .duration_since(time::UNIX_EPOCH)
+            .expect(
+                "process start time should not be before the beginning \
+                 of the Unix epoch"
+            )
+            .as_secs();
+
+        let request_total = Metric::<Counter, Arc<RequestLabels>>::new(
+            "request_total",
+            "A counter of the number of requests the proxy has received.",
+        );
+
+        let request_duration = Metric::<Histogram, Arc<RequestLabels>>::new(
+            "request_duration_ms",
+            "A histogram of the duration of a request. This is measured from \
+             when the request headers are received to when the request \
+             stream has completed.",
+        );
+
+        let response_total = Metric::<Counter, Arc<ResponseLabels>>::new(
+            "response_total",
+            "A counter of the number of responses the proxy has received.",
+        );
+
+        let response_duration = Metric::<Histogram, Arc<ResponseLabels>>::new(
+            "response_duration_ms",
+            "A histogram of the duration of a response. This is measured from \
+             when the response headers are received to when the response \
+             stream has completed.",
+        );
+
+        let response_latency = Metric::<Histogram, Arc<ResponseLabels>>::new(
+            "response_latency_ms",
+            "A histogram of the total latency of a response. This is measured \
+            from when the request headers are received to when the response \
+            stream has completed.",
+        );
+
+        Metrics {
+            request_total,
+            request_duration,
+            response_total,
+            response_duration,
+            response_latency,
+            start_time,
+        }
+    }
+
+    fn request_total(&mut self,
+                     labels: &Arc<RequestLabels>)
+                     -> &mut Counter {
+        self.request_total.values
+            .entry(labels.clone())
+            .or_insert_with(Default::default)
+    }
+
+    fn request_duration(&mut self,
+                        labels: &Arc<RequestLabels>)
+                        -> &mut Histogram {
+        self.request_duration.values
+            .entry(labels.clone())
+            .or_insert_with(Default::default)
+    }
+
+    fn response_duration(&mut self,
+                         labels: &Arc<ResponseLabels>)
+                         -> &mut Histogram {
+        self.response_duration.values
+            .entry(labels.clone())
+            .or_insert_with(Default::default)
+    }
+
+    fn response_latency(&mut self,
+                        labels: &Arc<ResponseLabels>)
+                        -> &mut Histogram {
+        self.response_latency.values
+            .entry(labels.clone())
+            .or_insert_with(Default::default)
+    }
+
+    fn response_total(&mut self,
+                      labels: &Arc<ResponseLabels>)
+                      -> &mut Counter {
+        self.response_total.values
+            .entry(labels.clone())
+            .or_insert_with(Default::default)
+    }
+}
+
+
+impl fmt::Display for Metrics {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "{}\n{}\n{}\n{}\n{}\nprocess_start_time_seconds {}\n",
+            self.request_total,
+            self.request_duration,
+            self.response_total,
+            self.response_duration,
+            self.response_latency,
+            self.start_time,
+        )
+    }
+}
+
+
+// ===== impl Counter =====
+
+impl fmt::Display for Counter {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "{}", (self.0).0 as f64)
+    }
+}
+
+impl Into<u64> for Counter {
+    fn into(self) -> u64 {
+        (self.0).0 as u64
+    }
+}
+
+impl ops::Add for Counter {
+    type Output = Self;
+    fn add(self, Counter(rhs): Self) -> Self::Output {
+        Counter(self.0 + rhs)
+    }
+}
+
+impl Counter {
+
+    /// Increment the counter by one.
+    ///
+    /// This function wraps on overflows.
+    pub fn incr(&mut self) -> &mut Self {
+        (*self).0 += Wrapping(1);
+        self
+    }
+}
+
+// ===== impl Metric =====
+
+impl<M, L: Hash + Eq> Metric<M, L> {
+
+    pub fn new(name: &'static str, help: &'static str) -> Self {
+        Metric {
+            name,
+            help,
+            values: IndexMap::new(),
+        }
+    }
+
+}
+
+impl<L> fmt::Display for Metric<Counter, L>
+where
+    L: fmt::Display,
+    L: Hash + Eq,
+{
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f,
+            "# HELP {name} {help}\n# TYPE {name} counter\n",
+            name = self.name,
+            help = self.help,
+        )?;
+
+        for (labels, value) in &self.values {
+            write!(f, "{name}{{{labels}}} {value}\n",
+                name = self.name,
+                labels = labels,
+                value = value,
+            )?;
+        }
+
+        Ok(())
+    }
+}
+
+impl<L> fmt::Display for Metric<Histogram, L> where
+    L: fmt::Display,
+    L: Hash + Eq,
+{
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f,
+            "# HELP {name} {help}\n# TYPE {name} histogram\n",
+            name = self.name,
+            help = self.help,
+        )?;
+
+        for (labels, histogram) in &self.values {
+            // Look up the bucket numbers against the BUCKET_BOUNDS array
+            // to turn them into upper bounds.
+            let bounds_and_counts = histogram.into_iter()
+                .enumerate()
+                .map(|(num, count)| (BUCKET_BOUNDS[num], count));
+
+            // Since Prometheus expects each bucket's value to be the sum of
+            // the number of values in this bucket and all lower buckets,
+            // track the total count here.
+            let mut total_count = 0;
+            for (le, count) in bounds_and_counts {
+                // Add this bucket's count to the total count.
+                total_count += count;
+                write!(f, "{name}_bucket{{{labels},le=\"{le}\"}} {count}\n",
+                    name = self.name,
+                    labels = labels,
+                    le = le,
+                    // Print the total count *as of this iteration*.
+                    count = total_count,
+                )?;
+            }
+
+            // Print the total count and histogram sum stats.
+            write!(f,
+                "{name}_count{{{labels}}} {count}\n\
+                 {name}_sum{{{labels}}} {sum}\n",
+                name = self.name,
+                labels = labels,
+                count = total_count,
+                sum = histogram.sum_in_ms(),
+            )?;
+        }
+
+        Ok(())
+    }
+}
+
+// ===== impl Aggregate =====
+
+impl Aggregate {
+
+    fn new(metrics: &Arc<Mutex<Metrics>>) -> Self {
+        Aggregate {
+            metrics: metrics.clone(),
+        }
+    }
+
+    #[inline]
+    fn update<F: Fn(&mut Metrics)>(&mut self, f: F) {
+        let mut lock = self.metrics.lock()
+            .expect("metrics lock poisoned");
+        f(&mut *lock);
+    }
+
+    /// Observe the given event.
+    pub fn record_event(&mut self, event: &Event) {
+        trace!("Metrics::record({:?})", event);
+        match *event {
+
+            Event::StreamRequestOpen(_) | Event::StreamResponseOpen(_, _) => {
+                // Do nothing; we'll record metrics for the request or response
+                //  when the stream *finishes*.
+            },
+
+            Event::StreamRequestFail(ref req, ref fail) => {
+                let labels = Arc::new(RequestLabels::new(req));
+                self.update(|metrics| {
+                    *metrics.request_duration(&labels) +=
+                        fail.since_request_open;
+                    *metrics.request_total(&labels).incr();
+                })
+            },
+
+            Event::StreamRequestEnd(ref req, ref end) => {
+                let labels = Arc::new(RequestLabels::new(req));
+                self.update(|metrics| {
+                    *metrics.request_total(&labels).incr();
+                    *metrics.request_duration(&labels) +=
+                        end.since_request_open;
+                })
+            },
+
+            Event::StreamResponseEnd(ref res, ref end) => {
+                let labels = Arc::new(ResponseLabels::new(
+                    res,
+                    end.grpc_status,
+                ));
+                self.update(|metrics| {
+                    *metrics.response_total(&labels).incr();
+                    *metrics.response_duration(&labels) +=  end.since_response_open;
+                    *metrics.response_latency(&labels) += end.since_request_open;
+                });
+            },
+
+            Event::StreamResponseFail(ref res, ref fail) => {
+                // TODO: do we care about the failure's error code here?
+                let labels = Arc::new(ResponseLabels::fail(res));
+                self.update(|metrics| {
+                    *metrics.response_total(&labels).incr();
+                    *metrics.response_duration(&labels) += fail.since_response_open;
+                    *metrics.response_latency(&labels) += fail.since_request_open;
+                });
+            },
+
+            Event::TransportOpen(_) | Event::TransportClose(_, _) => {
+                // TODO: we don't collect any metrics around transport events.
+            },
+        };
+    }
+}
+
+
+// ===== impl Serve =====
+
+impl Serve {
+    fn new(metrics: &Arc<Mutex<Metrics>>) -> Self {
+        Serve { metrics: metrics.clone() }
+    }
+}
+
+impl HyperService for Serve {
+    type Request = HyperRequest;
+    type Response = HyperResponse;
+    type Error = hyper::Error;
+    type Future = FutureResult<Self::Response, Self::Error>;
+
+    fn call(&self, req: Self::Request) -> Self::Future {
+        if req.path() != "/metrics" {
+            return future::ok(HyperResponse::new()
+                .with_status(StatusCode::NotFound));
+        }
+
+        let body = {
+            let metrics = self.metrics.lock()
+                .expect("metrics lock poisoned");
+            format!("{}", *metrics)
+        };
+        future::ok(HyperResponse::new()
+            .with_header(ContentLength(body.len() as u64))
+            .with_header(ContentType::plaintext())
+            .with_body(body))
+    }
+}

proxy/src/telemetry/metrics/prometheus/mod.rs

@@ -1,453 +0,0 @@
-//! Aggregates and serves Prometheus metrics.
-//!
-//! # A note on label formatting
-//!
-//! Prometheus labels are represented as a comma-separated list of values
-//! Since the Conduit proxy labels its metrics with a fixed set of labels
-//! which we know in advance, we represent these labels using a number of
-//! `struct`s, all of which implement `fmt::Display`. Some of the label
-//! `struct`s contain other structs which represent a subset of the labels
-//! which can be present on metrics in that scope. In this case, the
-//! `fmt::Display` impls for those structs call the `fmt::Display` impls for
-//! the structs that they own. This has the potential to complicate the
-//! insertion of commas to separate label values.
-//!
-//! In order to ensure that commas are added correctly to separate labels,
-//! we expect the `fmt::Display` implementations for label types to behave in
-//! a consistent way: A label struct is *never* responsible for printing
-//! leading or trailing commas before or after the label values it contains.
-//! If it contains multiple labels, it *is* responsible for ensuring any
-//! labels it owns are comma-separated. This way, the `fmt::Display` impl for
-//! any struct that represents a subset of the labels are position-agnostic;
-//! they don't need to know if there are other labels before or after them in
-//! the formatted output. The owner is responsible for managing that.
-//!
-//! If this rule is followed consistently across all structs representing
-//! labels, we can add new labels or modify the existing ones without having
-//! to worry about missing commas, double commas, or trailing commas at the
-//! end of the label set (all of which will make Prometheus angry).
-use std::default::Default;
-use std::{fmt, ops, time};
-use std::hash::Hash;
-use std::num::Wrapping;
-use std::sync::{Arc, Mutex};
-
-use futures::future::{self, FutureResult};
-use hyper;
-use hyper::header::{ContentLength, ContentType};
-use hyper::StatusCode;
-use hyper::server::{
-    Service as HyperService,
-    Request as HyperRequest,
-    Response as HyperResponse
-};
-use indexmap::{IndexMap};
-
-use ctx;
-use telemetry::event::Event;
-use super::latency::{BUCKET_BOUNDS, Histogram};
-
-mod labels;
-use self::labels::{RequestLabels, ResponseLabels};
-pub use self::labels::{DstLabels, Labeled};
-
-#[derive(Debug, Clone)]
-struct Metrics {
-    request_total: Metric<Counter, Arc<RequestLabels>>,
-    request_duration: Metric<Histogram, Arc<RequestLabels>>,
-
-    response_total: Metric<Counter, Arc<ResponseLabels>>,
-    response_duration: Metric<Histogram, Arc<ResponseLabels>>,
-    response_latency: Metric<Histogram, Arc<ResponseLabels>>,
-
-    start_time: u64,
-}
-
-#[derive(Debug, Clone)]
-struct Metric<M, L: Hash + Eq> {
-    name: &'static str,
-    help: &'static str,
-    values: IndexMap<L, M>
-}
-
-/// A Prometheus counter is represented by a `Wrapping` unsigned 64-bit int.
-///
-/// Counters always explicitly wrap on overflows rather than panicking in
-/// debug builds. Prometheus' [`rate()`] and [`irate()`] queries handle breaks
-/// in monotonicity gracefully  (see also [`resets()`]), so wrapping is less
-/// problematic than panicking in this case.
-///
-/// Note, however, that Prometheus represents counters using 64-bit
-/// floating-point numbers. The correct semantics are to ensure the counter
-/// always gets reset to zero after Prometheus reads it, before it would ever
-/// overflow a 52-bit `f64` mantissa.
-///
-/// [`rate()`]: https://prometheus.io/docs/prometheus/latest/querying/functions/#rate()
-/// [`irate()`]: https://prometheus.io/docs/prometheus/latest/querying/functions/#irate()
-/// [`resets()`]: https://prometheus.io/docs/prometheus/latest/querying/functions/#resets
-///
-// TODO: Implement Prometheus reset semantics correctly, taking into
-//       consideration that Prometheus models counters as `f64` and so
-//       there are only 52 significant bits.
-#[derive(Copy, Debug, Default, Clone, Eq, PartialEq)]
-pub struct Counter(Wrapping<u64>);
-
-/// Tracks Prometheus metrics
-#[derive(Debug)]
-pub struct Aggregate {
-    metrics: Arc<Mutex<Metrics>>,
-}
-
-/// Serve Prometheues metrics.
-#[derive(Debug, Clone)]
-pub struct Serve {
-    metrics: Arc<Mutex<Metrics>>,
-}
-
-/// Construct the Prometheus metrics.
-///
-/// Returns the `Aggregate` and `Serve` sides. The `Serve` side
-/// is a Hyper service which can be used to create the server for the
-/// scrape endpoint, while the `Aggregate` side can receive updates to the
-/// metrics by calling `record_event`.
-pub fn new(process: &Arc<ctx::Process>) -> (Aggregate, Serve) {
-    let metrics = Arc::new(Mutex::new(Metrics::new(process)));
-    (Aggregate::new(&metrics), Serve::new(&metrics))
-}
-
-// ===== impl Metrics =====
-
-impl Metrics {
-
-    pub fn new(process: &Arc<ctx::Process>) -> Self {
-
-        let start_time = process.start_time
-            .duration_since(time::UNIX_EPOCH)
-            .expect(
-                "process start time should not be before the beginning \
-                 of the Unix epoch"
-            )
-            .as_secs();
-
-        let request_total = Metric::<Counter, Arc<RequestLabels>>::new(
-            "request_total",
-            "A counter of the number of requests the proxy has received.",
-        );
-
-        let request_duration = Metric::<Histogram, Arc<RequestLabels>>::new(
-            "request_duration_ms",
-            "A histogram of the duration of a request. This is measured from \
-             when the request headers are received to when the request \
-             stream has completed.",
-        );
-
-        let response_total = Metric::<Counter, Arc<ResponseLabels>>::new(
-            "response_total",
-            "A counter of the number of responses the proxy has received.",
-        );
-
-        let response_duration = Metric::<Histogram, Arc<ResponseLabels>>::new(
-            "response_duration_ms",
-            "A histogram of the duration of a response. This is measured from \
-             when the response headers are received to when the response \
-             stream has completed.",
-        );
-
-        let response_latency = Metric::<Histogram, Arc<ResponseLabels>>::new(
-            "response_latency_ms",
-            "A histogram of the total latency of a response. This is measured \
-            from when the request headers are received to when the response \
-            stream has completed.",
-        );
-
-        Metrics {
-            request_total,
-            request_duration,
-            response_total,
-            response_duration,
-            response_latency,
-            start_time,
-        }
-    }
-
-    fn request_total(&mut self,
-                     labels: &Arc<RequestLabels>)
-                     -> &mut Counter {
-        self.request_total.values
-            .entry(labels.clone())
-            .or_insert_with(Default::default)
-    }
-
-    fn request_duration(&mut self,
-                        labels: &Arc<RequestLabels>)
-                        -> &mut Histogram {
-        self.request_duration.values
-            .entry(labels.clone())
-            .or_insert_with(Default::default)
-    }
-
-    fn response_duration(&mut self,
-                         labels: &Arc<ResponseLabels>)
-                         -> &mut Histogram {
-        self.response_duration.values
-            .entry(labels.clone())
-            .or_insert_with(Default::default)
-    }
-
-    fn response_latency(&mut self,
-                        labels: &Arc<ResponseLabels>)
-                        -> &mut Histogram {
-        self.response_latency.values
-            .entry(labels.clone())
-            .or_insert_with(Default::default)
-    }
-
-    fn response_total(&mut self,
-                      labels: &Arc<ResponseLabels>)
-                      -> &mut Counter {
-        self.response_total.values
-            .entry(labels.clone())
-            .or_insert_with(Default::default)
-    }
-}
-
-
-impl fmt::Display for Metrics {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        write!(f, "{}\n{}\n{}\n{}\n{}\nprocess_start_time_seconds {}\n",
-            self.request_total,
-            self.request_duration,
-            self.response_total,
-            self.response_duration,
-            self.response_latency,
-            self.start_time,
-        )
-    }
-}
-
-
-// ===== impl Counter =====
-
-impl fmt::Display for Counter {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        write!(f, "{}", (self.0).0 as f64)
-    }
-}
-
-impl Into<u64> for Counter {
-    fn into(self) -> u64 {
-        (self.0).0 as u64
-    }
-}
-
-impl ops::Add for Counter {
-    type Output = Self;
-    fn add(self, Counter(rhs): Self) -> Self::Output {
-        Counter(self.0 + rhs)
-    }
-}
-
-impl Counter {
-
-    /// Increment the counter by one.
-    ///
-    /// This function wraps on overflows.
-    pub fn incr(&mut self) -> &mut Self {
-        (*self).0 += Wrapping(1);
-        self
-    }
-}
-
-// ===== impl Metric =====
-
-impl<M, L: Hash + Eq> Metric<M, L> {
-
-    pub fn new(name: &'static str, help: &'static str) -> Self {
-        Metric {
-            name,
-            help,
-            values: IndexMap::new(),
-        }
-    }
-
-}
-
-impl<L> fmt::Display for Metric<Counter, L>
-where
-    L: fmt::Display,
-    L: Hash + Eq,
-{
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        write!(f,
-            "# HELP {name} {help}\n# TYPE {name} counter\n",
-            name = self.name,
-            help = self.help,
-        )?;
-
-        for (labels, value) in &self.values {
-            write!(f, "{name}{{{labels}}} {value}\n",
-                name = self.name,
-                labels = labels,
-                value = value,
-            )?;
-        }
-
-        Ok(())
-    }
-}
-
-impl<L> fmt::Display for Metric<Histogram, L> where
-    L: fmt::Display,
-    L: Hash + Eq,
-{
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        write!(f,
-            "# HELP {name} {help}\n# TYPE {name} histogram\n",
-            name = self.name,
-            help = self.help,
-        )?;
-
-        for (labels, histogram) in &self.values {
-            // Look up the bucket numbers against the BUCKET_BOUNDS array
-            // to turn them into upper bounds.
-            let bounds_and_counts = histogram.into_iter()
-                .enumerate()
-                .map(|(num, count)| (BUCKET_BOUNDS[num], count));
-
-            // Since Prometheus expects each bucket's value to be the sum of
-            // the number of values in this bucket and all lower buckets,
-            // track the total count here.
-            let mut total_count = 0;
-            for (le, count) in bounds_and_counts {
-                // Add this bucket's count to the total count.
-                total_count += count;
-                write!(f, "{name}_bucket{{{labels},le=\"{le}\"}} {count}\n",
-                    name = self.name,
-                    labels = labels,
-                    le = le,
-                    // Print the total count *as of this iteration*.
-                    count = total_count,
-                )?;
-            }
-
-            // Print the total count and histogram sum stats.
-            write!(f,
-                "{name}_count{{{labels}}} {count}\n\
-                 {name}_sum{{{labels}}} {sum}\n",
-                name = self.name,
-                labels = labels,
-                count = total_count,
-                sum = histogram.sum_in_ms(),
-            )?;
-        }
-
-        Ok(())
-    }
-}
-
-// ===== impl Aggregate =====
-
-impl Aggregate {
-
-    fn new(metrics: &Arc<Mutex<Metrics>>) -> Self {
-        Aggregate {
-            metrics: metrics.clone(),
-        }
-    }
-
-    #[inline]
-    fn update<F: Fn(&mut Metrics)>(&mut self, f: F) {
-        let mut lock = self.metrics.lock()
-            .expect("metrics lock poisoned");
-        f(&mut *lock);
-    }
-
-    /// Observe the given event.
-    pub fn record_event(&mut self, event: &Event) {
-        trace!("Metrics::record({:?})", event);
-        match *event {
-
-            Event::StreamRequestOpen(_) | Event::StreamResponseOpen(_, _) => {
-                // Do nothing; we'll record metrics for the request or response
-                //  when the stream *finishes*.
-            },
-
-            Event::StreamRequestFail(ref req, ref fail) => {
-                let labels = Arc::new(RequestLabels::new(req));
-                self.update(|metrics| {
-                    *metrics.request_duration(&labels) +=
-                        fail.since_request_open;
-                    *metrics.request_total(&labels).incr();
-                })
-            },
-
-            Event::StreamRequestEnd(ref req, ref end) => {
-                let labels = Arc::new(RequestLabels::new(req));
-                self.update(|metrics| {
-                    *metrics.request_total(&labels).incr();
-                    *metrics.request_duration(&labels) +=
-                        end.since_request_open;
-                })
-            },
-
-            Event::StreamResponseEnd(ref res, ref end) => {
-                let labels = Arc::new(ResponseLabels::new(
-                    res,
-                    end.grpc_status,
-                ));
-                self.update(|metrics| {
-                    *metrics.response_total(&labels).incr();
-                    *metrics.response_duration(&labels) +=  end.since_response_open;
-                    *metrics.response_latency(&labels) += end.since_request_open;
-                });
-            },
-
-            Event::StreamResponseFail(ref res, ref fail) => {
-                // TODO: do we care about the failure's error code here?
-                let labels = Arc::new(ResponseLabels::fail(res));
-                self.update(|metrics| {
-                    *metrics.response_total(&labels).incr();
-                    *metrics.response_duration(&labels) += fail.since_response_open;
-                    *metrics.response_latency(&labels) += fail.since_request_open;
-                });
-            },
-
-            Event::TransportOpen(_) | Event::TransportClose(_, _) => {
-                // TODO: we don't collect any metrics around transport events.
-            },
-        };
-    }
-}
-
-
-// ===== impl Serve =====
-
-impl Serve {
-    fn new(metrics: &Arc<Mutex<Metrics>>) -> Self {
-        Serve { metrics: metrics.clone() }
-    }
-}
-
-impl HyperService for Serve {
-    type Request = HyperRequest;
-    type Response = HyperResponse;
-    type Error = hyper::Error;
-    type Future = FutureResult<Self::Response, Self::Error>;
-
-    fn call(&self, req: Self::Request) -> Self::Future {
-        if req.path() != "/metrics" {
-            return future::ok(HyperResponse::new()
-                .with_status(StatusCode::NotFound));
-        }
-
-        let body = {
-            let metrics = self.metrics.lock()
-                .expect("metrics lock poisoned");
-            format!("{}", *metrics)
-        };
-        future::ok(HyperResponse::new()
-            .with_header(ContentLength(body.len() as u64))
-            .with_header(ContentType::plaintext())
-            .with_body(body))
-    }
-}