discovery:kube: Support wildcard matching for ingress rules

This change sets the scheme to https when a rule specified by Ingress
matches a wildcard DNS entry in the ingress TLS hosts

Signed-off-by: Philip Gough <philip.p.gough@gmail.com>

discovery/kubernetes/ingress.go

@@ -15,6 +15,7 @@ package kubernetes
 
 import (
 	"context"
+	"strings"
 
 	"github.com/go-kit/log"
 	"github.com/go-kit/log/level"
@@ -193,18 +194,16 @@ func (i *Ingress) buildIngress(ingress ingressAdaptor) *targetgroup.Group {
 	}
 	tg.Labels = ingressLabels(ingress)
 
-	tlsHosts := make(map[string]struct{})
-	for _, host := range ingress.tlsHosts() {
-		tlsHosts[host] = struct{}{}
-	}
-
 	for _, rule := range ingress.rules() {
+		scheme := "http"
 		paths := pathsFromIngressPaths(rule.paths())
 
-		scheme := "http"
-		_, isTLS := tlsHosts[rule.host()]
-		if isTLS {
-			scheme = "https"
+	out:
+		for _, pattern := range ingress.tlsHosts() {
+			if matchesHostnamePattern(pattern, rule.host()) {
+				scheme = "https"
+				break out
+			}
 		}
 
 		for _, path := range paths {
@@ -219,3 +218,34 @@ func (i *Ingress) buildIngress(ingress ingressAdaptor) *targetgroup.Group {
 
 	return tg
 }
+
+// matchesHostnamePattern returns true if the host matches a wildcard DNS
+// pattern or pattern and host are equal
+func matchesHostnamePattern(pattern, host string) bool {
+	// check for exact match
+	if pattern == host {
+		return true
+	}
+
+	patternParts := strings.Split(pattern, ".")
+	hostParts := strings.Split(host, ".")
+
+	// if they are not equal, we cna check if we need to match
+	// on a wildcard or else give up
+	if len(patternParts) == 0 || patternParts[0] != "*" {
+		return false
+	}
+
+	// to get a valid wildcard match the parts will need to be the same length
+	if len(patternParts) != len(hostParts) {
+		return false
+	}
+
+	for i := 1; i < len(patternParts); i++ {
+		if patternParts[i] != hostParts[i] {
+			return false
+		}
+	}
+
+	return true
+}

discovery/kubernetes/ingress_test.go

@@ -19,11 +19,11 @@ import (
 	"testing"
 
 	"github.com/prometheus/common/model"
+	"github.com/prometheus/prometheus/discovery/targetgroup"
+
 	v1 "k8s.io/api/networking/v1"
 	"k8s.io/api/networking/v1beta1"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
-
-	"github.com/prometheus/prometheus/discovery/targetgroup"
 )
 
 type TLSMode int
@@ -32,6 +32,7 @@ const (
 	TLSNo TLSMode = iota
 	TLSYes
 	TLSMixed
+	TLSWildcard
 )
 
 func makeIngress(tls TLSMode) *v1.Ingress {
@@ -81,6 +82,8 @@ func makeIngress(tls TLSMode) *v1.Ingress {
 		ret.Spec.TLS = []v1.IngressTLS{{Hosts: []string{"example.com", "test.example.com"}}}
 	case TLSMixed:
 		ret.Spec.TLS = []v1.IngressTLS{{Hosts: []string{"example.com"}}}
+	case TLSWildcard:
+		ret.Spec.TLS = []v1.IngressTLS{{Hosts: []string{"*.example.com"}}}
 	}
 
 	return ret
@@ -133,6 +136,8 @@ func makeIngressV1beta1(tls TLSMode) *v1beta1.Ingress {
 		ret.Spec.TLS = []v1beta1.IngressTLS{{Hosts: []string{"example.com", "test.example.com"}}}
 	case TLSMixed:
 		ret.Spec.TLS = []v1beta1.IngressTLS{{Hosts: []string{"example.com"}}}
+	case TLSWildcard:
+		ret.Spec.TLS = []v1beta1.IngressTLS{{Hosts: []string{"*.example.com"}}}
 	}
 
 	return ret
@@ -152,6 +157,8 @@ func expectedTargetGroups(ns string, tls TLSMode) map[string]*targetgroup.Group
 		scheme2 = "https"
 	case TLSMixed:
 		scheme1 = "https"
+	case TLSWildcard:
+		scheme2 = "https"
 	}
 
 	key := fmt.Sprintf("ingress/%s/testingress", ns)