Export the versions of Go modules linked into the binary

baseplate.go

@@ -5,13 +5,15 @@ import (
 	"fmt"
 	"io"
 	"os"
+	"runtime/debug"
 	"time"
 
 	"github.com/reddit/baseplate.go/batchcloser"
 	"github.com/reddit/baseplate.go/configbp"
 	"github.com/reddit/baseplate.go/ecinterface"
 	"github.com/reddit/baseplate.go/log"
 	"github.com/reddit/baseplate.go/metricsbp"
+	"github.com/reddit/baseplate.go/prometheusbp"
 	"github.com/reddit/baseplate.go/runtimebp"
 	"github.com/reddit/baseplate.go/secrets"
 	"github.com/reddit/baseplate.go/tracing"
@@ -307,6 +309,12 @@ func New(ctx context.Context, args NewArgs) (context.Context, Baseplate, error)
 	cfg := args.Config.GetConfig()
 	bp := impl{cfg: cfg, closers: batchcloser.New()}
 
+	if info, ok := debug.ReadBuildInfo(); ok {
+		prometheusbp.RecordModuleVersions(info)
+	} else {
+		log.C(ctx).Warn("baseplate.New: unable to read build info to export dependency metrics")
+	}
+
 	runtimebp.InitFromConfig(cfg.Runtime)
 
 	ctx, cancel := context.WithCancel(ctx)

prometheusbp/modules.go

@@ -0,0 +1,38 @@
+package prometheusbp
+
+import (
+	"runtime/debug"
+	"strconv"
+
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promauto"
+
+	"github.com/reddit/baseplate.go/internal/prometheusbpint"
+)
+
+var goModules = promauto.With(prometheusbpint.GlobalRegistry).NewGaugeVec(prometheus.GaugeOpts{
+	Name: "baseplate_go_modules",
+	Help: "Export the version information for included Go modules, and whether the module is the 'main' module or a 'dependency'.  Always 1",
+}, []string{"go_module", "module_role", "module_replaced", "module_version"})
+
+// RecordModuleVersions records the modules linked into this binary in the
+// baseplate_go_modules prometheus metric.
+//
+// Users should not need to call this directly, as it is called by baseplate.New.
+// This should generally not be called more than once, and it is not safe to call concurrently.
+func RecordModuleVersions(info *debug.BuildInfo) {
+	record := func(role string, mod *debug.Module) {
+		goModules.With(prometheus.Labels{
+			"go_module":       mod.Path,
+			"module_role":     role,
+			"module_replaced": strconv.FormatBool(mod.Replace != nil),
+			"module_version":  mod.Version,
+		}).Set(1)
+	}
+
+	goModules.Reset()
+	record("main", &info.Main)
+	for _, dep := range info.Deps {
+		record("dependency", dep)
+	}
+}

prometheusbp/modules_test.go

@@ -0,0 +1,55 @@
+package prometheusbp
+
+import (
+	"runtime/debug"
+	"testing"
+
+	"github.com/prometheus/client_golang/prometheus"
+
+	"github.com/reddit/baseplate.go/prometheusbp/promtest"
+)
+
+func TestBuildInfoMetrics(t *testing.T) {
+	info := &debug.BuildInfo{
+		GoVersion: "go1.18.3",
+		Path:      "example.com/path/to/main/module",
+		Main: debug.Module{
+			Path:    "example.com/path/to/main/module",
+			Version: "(devel)",
+		},
+		Deps: []*debug.Module{{
+			Path:    "github.com/reddit/baseplate.go",
+			Version: "v1.2.3",
+		}, {
+			Path: "github.com/reddit/oldmodule",
+			Replace: &debug.Module{
+				Path:    "github.com/reddit/newmodule",
+				Version: "v1.42.0",
+			},
+			Version: "v0.1.2",
+		}},
+	}
+
+	defer promtest.NewPrometheusMetricTest(t, "baseplate_go_modules", goModules, prometheus.Labels{
+		"go_module":       "example.com/path/to/main/module",
+		"module_role":     "main",
+		"module_replaced": "false",
+		"module_version":  "(devel)",
+	}).CheckDelta(1)
+
+	defer promtest.NewPrometheusMetricTest(t, "baseplate_go_modules", goModules, prometheus.Labels{
+		"go_module":       "github.com/reddit/baseplate.go",
+		"module_role":     "dependency",
+		"module_replaced": "false",
+		"module_version":  "v1.2.3",
+	}).CheckDelta(1)
+
+	defer promtest.NewPrometheusMetricTest(t, "baseplate_go_modules", goModules, prometheus.Labels{
+		"go_module":       "github.com/reddit/oldmodule",
+		"module_role":     "dependency",
+		"module_replaced": "true",
+		"module_version":  "v0.1.2",
+	}).CheckDelta(1)
+
+	RecordModuleVersions(info)
+}