Early filter of the catalog services.

docs/content/providers/consul-catalog.md

@@ -565,7 +565,7 @@ Constraints is an expression that Traefik matches against the service's tags to
 That is to say, if none of the service's tags match the expression, no route for that service is created.
 If the expression is empty, all detected services are included.
 
-The expression syntax is based on the `Tag("tag")`, and `TagRegex("tag")` functions,
+The expression syntax is based on the ```Tag(`tag`)```, and ```TagRegex(`tag`)``` functions,
 as well as the usual boolean logic, as shown in examples below.
 
 ??? example "Constraints Expression Examples"

integration/consul_catalog_test.go

@@ -128,7 +128,18 @@ func (s *ConsulCatalogSuite) TestWithNotExposedByDefaultAndDefaultsSettings(c *c
 	c.Assert(err, checker.IsNil)
 	req.Host = "whoami"
 
-	err = try.Request(req, 2*time.Second, try.StatusCodeIs(200), try.BodyContainsOr("Hostname: whoami1", "Hostname: whoami2", "Hostname: whoami3"))
+	err = try.Request(req, 2*time.Second,
+		try.StatusCodeIs(200),
+		try.BodyContainsOr("Hostname: whoami1", "Hostname: whoami2", "Hostname: whoami3"))
+	c.Assert(err, checker.IsNil)
+
+	err = try.GetRequest("http://127.0.0.1:8080/api/rawdata", 2*time.Second,
+		try.StatusCodeIs(200),
+		try.BodyContains(
+			fmt.Sprintf(`"http://%s:80":"UP"`, reg1.Address),
+			fmt.Sprintf(`"http://%s:80":"UP"`, reg2.Address),
+			fmt.Sprintf(`"http://%s:80":"UP"`, reg3.Address),
+		))
 	c.Assert(err, checker.IsNil)
 
 	err = s.deregisterService("whoami1", false)

pkg/provider/consulcatalog/consul_catalog.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"fmt"
 	"strconv"
+	"strings"
 	"text/template"
 	"time"
 
@@ -12,6 +13,7 @@ import (
 	"github.com/containous/traefik/v2/pkg/job"
 	"github.com/containous/traefik/v2/pkg/log"
 	"github.com/containous/traefik/v2/pkg/provider"
+	"github.com/containous/traefik/v2/pkg/provider/constraints"
 	"github.com/containous/traefik/v2/pkg/safe"
 	"github.com/containous/traefik/v2/pkg/types"
 	"github.com/hashicorp/consul/api"
@@ -151,7 +153,7 @@ func (p *Provider) getConsulServicesData(ctx context.Context) ([]itemData, error
 	}
 
 	var data []itemData
-	for name := range consulServiceNames {
+	for _, name := range consulServiceNames {
 		consulServices, healthServices, err := p.fetchService(ctx, name)
 		if err != nil {
 			return nil, err
@@ -204,10 +206,55 @@ func (p *Provider) fetchService(ctx context.Context, name string) ([]*api.Catalo
 	return consulServices, healthServices, err
 }
 
-func (p *Provider) fetchServices(ctx context.Context) (map[string][]string, error) {
+func (p *Provider) fetchServices(ctx context.Context) ([]string, error) {
+	// The query option "Filter" is not supported by /catalog/services.
+	// https://www.consul.io/api/catalog.html#list-services
 	opts := &api.QueryOptions{AllowStale: p.Stale, RequireConsistent: p.RequireConsistent, UseCache: p.Cache}
 	serviceNames, _, err := p.client.Catalog().Services(opts)
-	return serviceNames, err
+	if err != nil {
+		return nil, err
+	}
+
+	// The keys are the service names, and the array values provide all known tags for a given service.
+	// https://www.consul.io/api/catalog.html#list-services
+	var filtered []string
+	for svcName, tags := range serviceNames {
+		logger := log.FromContext(log.With(ctx, log.Str("serviceName", svcName)))
+
+		if !p.ExposedByDefault && !contains(tags, p.Prefix+".enable=true") {
+			logger.Debug("Filtering disabled item")
+			continue
+		}
+
+		if contains(tags, p.Prefix+".enable=false") {
+			logger.Debug("Filtering disabled item")
+			continue
+		}
+
+		matches, err := constraints.MatchTags(tags, p.Constraints)
+		if err != nil {
+			logger.Errorf("Error matching constraints expression: %v", err)
+			continue
+		}
+
+		if !matches {
+			logger.Debugf("Container pruned by constraint expression: %q", p.Constraints)
+			continue
+		}
+
+		filtered = append(filtered, svcName)
+	}
+
+	return filtered, err
+}
+
+func contains(values []string, val string) bool {
+	for _, value := range values {
+		if strings.EqualFold(value, val) {
+			return true
+		}
+	}
+	return false
 }
 
 func createClient(cfg *EndpointConfig) (*api.Client, error) {