fix: Lowercase scheme for Prometheus ScrapeConfig

This fixes #3386

Signed-off-by: alex-berger <[email protected]>

Author: alex-berger

CHANGELOG.md

@@ -44,6 +44,7 @@ Main (unreleased)
 ### Bugfixes
 
 - Fix `otelcol.receiver.filelog` documentation's default value for `start_at`. (@petewall)
+- Fix [#3386](https://github.com/grafana/alloy/issues/3386) lower casing scheme in `prometheus.operator.scrapeconfigs`. (@alex-berger)
 - Fix `mimir.rules.kubernetes` panic on non-leader debug info retrieval (@TheoBrigitte)
 
 ### Other changes

internal/component/prometheus/operator/configgen/config_gen_scrapeconfig.go

@@ -4,6 +4,7 @@ package configgen
 
 import (
 	"fmt"
+	"strings"
 
 	promopv1alpha1 "github.com/prometheus-operator/prometheus-operator/pkg/apis/monitoring/v1alpha1"
 	"github.com/prometheus-operator/prometheus-operator/pkg/namespacelabeler"
@@ -92,7 +93,10 @@ func (cg *ConfigGenerator) commonScrapeConfigConfig(m *promopv1alpha1.ScrapeConf
 		cfg.Params = m.Spec.Params
 	}
 	if m.Spec.Scheme != nil {
-		cfg.Scheme = *m.Spec.Scheme
+		// Prometheus Operator ScrapeConfig CRD requires spec.scheme to be uppercase "HTTP" or "HTTPS", but
+		// the implementation expects lowercase "http" or "https" in the final scrape configuration. So, we
+		// have to lowercase the schema.
+		cfg.Scheme = strings.ToLower(*m.Spec.Scheme)
 	}
 	if m.Spec.TLSConfig != nil {
 		if cfg.HTTPClientConfig.TLSConfig, err = cg.generateSafeTLS(*m.Spec.TLSConfig, m.Namespace); err != nil {

internal/component/prometheus/operator/configgen/config_gen_scrapeconfig_test.go

@@ -26,6 +26,7 @@ import (
 )
 
 func TestGenerateStaticScrapeConfigConfig(t *testing.T) {
+	HTTPS := "HTTPS"
 	suite := []struct {
 		name                   string
 		m                      *promopv1alpha1.ScrapeConfig
@@ -84,6 +85,56 @@ func TestGenerateStaticScrapeConfigConfig(t *testing.T) {
 				},
 			},
 		},
+		{
+			name: "lowercase schema",
+			m: &promopv1alpha1.ScrapeConfig{
+				ObjectMeta: metav1.ObjectMeta{
+					Namespace: "operator",
+					Name:      "scrapeconfig",
+				},
+				Spec: promopv1alpha1.ScrapeConfigSpec{
+					Scheme: &HTTPS,
+				},
+			},
+			ep: promopv1alpha1.StaticConfig{
+				Targets: []promopv1alpha1.Target{"foo", "bar"},
+			},
+			expectedRelabels: util.Untab(`
+				- target_label: __meta_foo
+				  replacement: bar
+				- source_labels: [job]
+				  target_label: __tmp_prometheus_job_name
+				- replacement: operator
+				  target_label: __meta_kubernetes_scrapeconfig_namespace
+				- replacement: scrapeconfig
+				  target_label: __meta_kubernetes_scrapeconfig_name
+				- source_labels: [__address__]
+				  target_label: instance
+			`),
+			expected: &config.ScrapeConfig{
+				JobName:           "scrapeConfig/operator/scrapeconfig/static/1",
+				HonorTimestamps:   true,
+				ScrapeInterval:    model.Duration(time.Hour),
+				ScrapeTimeout:     model.Duration(42 * time.Second),
+				ScrapeProtocols:   config.DefaultScrapeProtocols,
+				EnableCompression: true,
+				MetricsPath:       "/metrics",
+				Scheme:            "https",
+				HTTPClientConfig: commonConfig.HTTPClientConfig{
+					FollowRedirects: true,
+					EnableHTTP2:     true,
+				},
+				ServiceDiscoveryConfigs: discovery.Configs{
+					discovery.StaticConfig{
+						&targetgroup.Group{
+							Targets: []model.LabelSet{{model.AddressLabel: model.LabelValue("foo")}, {model.AddressLabel: model.LabelValue("bar")}},
+							Labels:  model.LabelSet{},
+							Source:  "scrapeConfig/operator/scrapeconfig/static/1",
+						},
+					},
+				},
+			},
+		},
 	}
 	for _, tc := range suite {
 		t.Run(tc.name, func(t *testing.T) {