From b6a101cdfe327b839ced7cfc626c6bd78201ff0f Mon Sep 17 00:00:00 2001
From: Tom Clegg <tom@curii.com>
Date: Fri, 8 Apr 2022 16:05:26 -0400
Subject: [PATCH] 18794: Export config timestamp/hash as prometheus metric.

Arvados-DCO-1.1-Signed-off-by: Tom Clegg <tom@curii.com>
---
 lib/config/load.go      | 19 +++++++++++++++++++
 lib/config/load_test.go | 12 ++++++++++++
 lib/service/cmd.go      |  2 ++
 3 files changed, 33 insertions(+)

diff --git a/lib/config/load.go b/lib/config/load.go
index 28f300e3bb..d03ef5388d 100644
--- a/lib/config/load.go
+++ b/lib/config/load.go
@@ -6,6 +6,7 @@ package config
 
 import (
 	"bytes"
+	"crypto/sha256"
 	_ "embed"
 	"encoding/json"
 	"errors"
@@ -22,6 +23,7 @@ import (
 	"git.arvados.org/arvados.git/sdk/go/arvados"
 	"github.com/ghodss/yaml"
 	"github.com/imdario/mergo"
+	"github.com/prometheus/client_golang/prometheus"
 	"github.com/sirupsen/logrus"
 )
 
@@ -569,3 +571,20 @@ func (ldr *Loader) autofillPreemptible(label string, cc *arvados.Cluster) {
 	}
 
 }
+
+// RegisterMetrics registers metrics showing the timestamp and content
+// hash of the currently loaded config.
+//
+// Must not be called more than once for a given registry. Must not be
+// called before Load(). Metrics are not updated by subsequent calls
+// to Load().
+func (ldr *Loader) RegisterMetrics(reg *prometheus.Registry) {
+	vec := prometheus.NewGaugeVec(prometheus.GaugeOpts{
+		Namespace: "arvados",
+		Subsystem: "config",
+		Name:      "source_timestamp_seconds",
+		Help:      "Timestamp of config file when it was loaded.",
+	}, []string{"sha256"})
+	vec.WithLabelValues(fmt.Sprintf("%x", sha256.Sum256(ldr.configdata))).Set(float64(ldr.sourceTimestamp.UnixNano()) / 1e9)
+	reg.MustRegister(vec)
+}
diff --git a/lib/config/load_test.go b/lib/config/load_test.go
index cef7ea944b..b43cda38c8 100644
--- a/lib/config/load_test.go
+++ b/lib/config/load_test.go
@@ -20,6 +20,8 @@ import (
 	"git.arvados.org/arvados.git/sdk/go/arvados"
 	"git.arvados.org/arvados.git/sdk/go/ctxlog"
 	"github.com/ghodss/yaml"
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/common/expfmt"
 	"github.com/sirupsen/logrus"
 	"golang.org/x/sys/unix"
 	check "gopkg.in/check.v1"
@@ -798,5 +800,15 @@ func (s *LoadSuite) TestSourceTimestamp(c *check.C) {
 		c.Assert(err, check.IsNil)
 		c.Check(cfg.SourceTimestamp, check.Equals, cfg.SourceTimestamp.UTC())
 		c.Check(int(cfg.SourceTimestamp.Sub(trial.expectTime).Seconds()), check.Equals, 0)
+
+		var buf bytes.Buffer
+		reg := prometheus.NewRegistry()
+		ldr.RegisterMetrics(reg)
+		enc := expfmt.NewEncoder(&buf, expfmt.FmtText)
+		got, _ := reg.Gather()
+		for _, mf := range got {
+			enc.Encode(mf)
+		}
+		c.Check(buf.String(), check.Matches, `# HELP .*\n# TYPE .*\narvados_config_source_timestamp_seconds{sha256="83aea5d82eb1d53372cd65c936c60acc1c6ef946e61977bbca7cfea709d201a8"} \Q`+fmt.Sprintf("%g", float64(cfg.SourceTimestamp.UnixNano())/1e9)+`\E\n`)
 	}
 }
diff --git a/lib/service/cmd.go b/lib/service/cmd.go
index 1ed2ac1314..6f5efa5cb7 100644
--- a/lib/service/cmd.go
+++ b/lib/service/cmd.go
@@ -117,6 +117,8 @@ func (c *command) RunCommand(prog string, args []string, stdin io.Reader, stdout
 	ctx = context.WithValue(ctx, contextKeyURL{}, listenURL)
 
 	reg := prometheus.NewRegistry()
+	loader.RegisterMetrics(reg)
+
 	handler := c.newHandler(ctx, cluster, cluster.SystemRootToken, reg)
 	if err = handler.CheckHealth(); err != nil {
 		return 1
-- 
2.30.2