pkg/metrics: introduce v2 (scionproto#4530)

Introduce a v2 version of pkg/metrics. The current metrics package is
not optimal:
- Using objects that have been called with With allocated on each
increment/set value call.
- Having the option to call With ties consumer code with initialization
code.
- There is no way whether a counter is fully initialized with all
labels.

A full discussion can be found in
scionproto#4527.

The new v2 version is compatible with prometheus, so no explicit
conversion functions are offered, instead the prometheus creation
functions can be used directly.

So far the new library has been plugged in selected places. The
intention is that it will eventually replace the current library
completely, however doing so in a single sweep would be too extensive.

Author: lukedirtwalker

control/BUILD.bazel

@@ -28,6 +28,7 @@ go_library(
         "//pkg/grpc:go_default_library",
         "//pkg/log:go_default_library",
         "//pkg/metrics:go_default_library",
+        "//pkg/metrics/v2:go_default_library",
         "//pkg/private/ctrl/path_mgmt:go_default_library",
         "//pkg/private/prom:go_default_library",
         "//pkg/private/serrors:go_default_library",

control/observability.go

@@ -28,6 +28,7 @@ import (
 	cstrust "github.com/scionproto/scion/control/trust"
 	"github.com/scionproto/scion/pkg/addr"
 	"github.com/scionproto/scion/pkg/metrics"
+	metrics2 "github.com/scionproto/scion/pkg/metrics/v2"
 	"github.com/scionproto/scion/pkg/private/prom"
 	"github.com/scionproto/scion/pkg/private/serrors"
 	"github.com/scionproto/scion/pkg/scrypto"
@@ -82,7 +83,7 @@ type Metrics struct {
 	TrustTRCFileWritesTotal                *prometheus.CounterVec
 	SCIONNetworkMetrics                    snet.SCIONNetworkMetrics
 	SCIONPacketConnMetrics                 snet.SCIONPacketConnMetrics
-	SCMPErrors                             metrics.Counter
+	SCMPErrors                             metrics2.Counter
 	TopoLoader                             topology.LoaderMetrics
 	DRKeySecretValueQueriesTotal           *prometheus.CounterVec
 	DRKeyLevel1QueriesTotal                *prometheus.CounterVec

doc/dev/style/go.rst

@@ -113,29 +113,20 @@ metrics, and for operators to understand where metrics are coming from. As a
 bonus, we should leverage the type system to help us spot as many errors as
 possible.
 
-To write code that both includes metrics, and is testable, we use the
-`metric recommendations from the go-kit project <https://godoc.org/github.com/go-kit/kit/metrics>`__.
+To write code that both includes metrics, and is testable, we use the metric
+interfaces defined in the ``pkg/metrics/v2`` package.
 
-A simple example with labels (note that ``Foo``'s metrics can be unit tested by mocking the counter):
+A simple example with labels (note that ``Giant``'s metrics can be unit tested by
+mocking the counter):
 
-.. literalinclude:: /../pkg/metrics/metrics_test.go
-   :language: Go
-   :dedent: 1
-   :start-after: LITERALINCLUDE ExampleCounter_Interface START
-   :end-before: LITERALINCLUDE ExampleCounter_Interface END
-
-Calling code can later create ``Giant`` objects with Prometheus metric reporting
-by plugging a prometheus counter as the ``Counter``. The Prometheus objects can be
-obtained from the metrics packages in the following way:
-
-.. literalinclude:: /../pkg/metrics/metrics_test.go
+.. literalinclude:: /../pkg/metrics/v2/metrics_test.go
    :language: Go
    :dedent: 1
    :start-after: LITERALINCLUDE ExampleCounter_Implementation START
    :end-before: LITERALINCLUDE ExampleCounter_Implementation END
 
-In cases where performance is a concern, consider applying the labels outside of
-the performance-critical section.
+Calling code can later create ``Giant`` objects with Prometheus metric reporting
+by plugging a prometheus counter as the ``Counter`` as shown in the example.
 
 .. note::
    Some packages have ``metrics`` packages that define labels and initialize

gateway/BUILD.bazel

@@ -25,6 +25,7 @@ go_library(
         "//pkg/grpc:go_default_library",
         "//pkg/log:go_default_library",
         "//pkg/metrics:go_default_library",
+        "//pkg/metrics/v2:go_default_library",
         "//pkg/private/serrors:go_default_library",
         "//pkg/private/util:go_default_library",
         "//pkg/proto/gateway:go_default_library",

gateway/metrics.go

@@ -19,7 +19,7 @@ import (
 	"github.com/prometheus/client_golang/prometheus/promauto"
 
 	"github.com/scionproto/scion/pkg/addr"
-	"github.com/scionproto/scion/pkg/metrics"
+	"github.com/scionproto/scion/pkg/metrics/v2"
 	"github.com/scionproto/scion/pkg/snet"
 	snetmetrics "github.com/scionproto/scion/pkg/snet/metrics"
 )

gateway/pathhealth/BUILD.bazel

@@ -17,6 +17,7 @@ go_library(
         "//pkg/addr:go_default_library",
         "//pkg/log:go_default_library",
         "//pkg/metrics:go_default_library",
+        "//pkg/metrics/v2:go_default_library",
         "//pkg/private/common:go_default_library",
         "//pkg/private/ctrl/path_mgmt:go_default_library",
         "//pkg/private/serrors:go_default_library",

gateway/pathhealth/pathwatcher.go

@@ -25,6 +25,7 @@ import (
 	"github.com/scionproto/scion/pkg/addr"
 	"github.com/scionproto/scion/pkg/log"
 	"github.com/scionproto/scion/pkg/metrics"
+	metrics2 "github.com/scionproto/scion/pkg/metrics/v2"
 	"github.com/scionproto/scion/pkg/private/common"
 	"github.com/scionproto/scion/pkg/private/serrors"
 	"github.com/scionproto/scion/pkg/slayers/path/scion"
@@ -59,8 +60,9 @@ type DefaultPathWatcherFactory struct {
 	ProbesReceived func(remote addr.IA) metrics.Counter
 	// ProbesSendErrors keeps track of how many time sending probes failed per
 	// remote.
-	ProbesSendErrors       func(remote addr.IA) metrics.Counter
-	SCMPErrors             metrics.Counter
+	ProbesSendErrors func(remote addr.IA) metrics.Counter
+
+	SCMPErrors             metrics2.Counter
 	SCIONPacketConnMetrics snet.SCIONPacketConnMetrics
 }
 

pkg/log/BUILD.bazel

@@ -15,7 +15,7 @@ go_library(
     importpath = "github.com/scionproto/scion/pkg/log",
     visibility = ["//visibility:public"],
     deps = [
-        "//pkg/metrics:go_default_library",
+        "//pkg/metrics/v2:go_default_library",
         "//pkg/private/common:go_default_library",
         "//pkg/private/serrors:go_default_library",
         "//private/config:go_default_library",

pkg/log/options.go

@@ -18,7 +18,7 @@ import (
 	"go.uber.org/zap"
 	"go.uber.org/zap/zapcore"
 
-	"github.com/scionproto/scion/pkg/metrics"
+	"github.com/scionproto/scion/pkg/metrics/v2"
 )
 
 type options struct {

pkg/metrics/v2/BUILD.bazel

@@ -0,0 +1,24 @@
+load("//tools/lint:go.bzl", "go_library", "go_test")
+
+go_library(
+    name = "go_default_library",
+    srcs = [
+        "fakes.go",
+        "metrics.go",
+    ],
+    importpath = "github.com/scionproto/scion/pkg/metrics/v2",
+    visibility = ["//visibility:public"],
+)
+
+go_test(
+    name = "go_default_test",
+    srcs = [
+        "fakes_test.go",
+        "metrics_test.go",
+    ],
+    deps = [
+        ":go_default_library",
+        "@com_github_prometheus_client_golang//prometheus:go_default_library",
+        "@com_github_stretchr_testify//assert:go_default_library",
+    ],
+)