discovery/kubernetes: expose label_selector and field_selector

Close #6807

Co-authored-by @shuttie
Signed-off-by: Aleksandra Gacek <algacek@google.com>

config/config_test.go

@@ -806,7 +806,7 @@ var expectedErrors = []struct {
 		errMsg:   "role",
 	}, {
 		filename: "kubernetes_selectors_endpoints.bad.yml",
-		errMsg:   "endpoints role supports only pod, service and endpoints selectors",
+		errMsg:   "endpoints role supports only pod, service, endpoints selectors",
 	}, {
 		filename: "kubernetes_selectors_ingress.bad.yml",
 		errMsg:   "ingress role supports only ingress selectors",
@@ -822,6 +822,12 @@ var expectedErrors = []struct {
 	}, {
 		filename: "kubernetes_namespace_discovery.bad.yml",
 		errMsg:   "field foo not found in type kubernetes.plain",
+	}, {
+		filename: "kubernetes_selectors_duplicated_role.bad.yml",
+		errMsg:   "duplicated selector role: pod",
+	}, {
+		filename: "kubernetes_selectors_incorrect_selector.bad.yml",
+		errMsg:   "invalid selector: 'metadata.status-Running'; can't understand 'metadata.status-Running'",
 	}, {
 		filename: "kubernetes_bearertoken_basicauth.bad.yml",
 		errMsg:   "at most one of basic_auth, bearer_token & bearer_token_file must be configured",

config/testdata/kubernetes_selectors_duplicated_role.bad.yml

@@ -0,0 +1,11 @@
+scrape_configs:
+- job_name: prometheus
+  kubernetes_sd_configs:
+  - role: endpoints
+    selectors:
+    - role: "pod"
+      label: "foo=bar"
+      field: "metadata.status=Running"
+    - role: "pod"
+      label: "foo=bar"
+      field: "metadata.status=Running"

config/testdata/kubernetes_selectors_endpoints.bad.yml

@@ -3,12 +3,12 @@ scrape_configs:
     kubernetes_sd_configs:
       - role: endpoints
         selectors:
-          node:
-            label: "foo=bar"
-            field: "metadata.status=Running"
-          service:
-            label: "foo=bar"
-            field: "metadata.status=Running"
-          endpoints:
-            label: "foo=bar"
-            field: "metadata.status=Running"
+        - role: "node"
+          label: "foo=bar"
+          field: "metadata.status=Running"
+        - role: "service"
+          label: "foo=bar"
+          field: "metadata.status=Running"
+        - role: "endpoints"
+          label: "foo=bar"
+          field: "metadata.status=Running"

config/testdata/kubernetes_selectors_endpoints.good.yml

@@ -3,12 +3,12 @@ scrape_configs:
     kubernetes_sd_configs:
       - role: endpoints
         selectors:
-          pod:
-            label: "foo=bar"
-            field: "metadata.status=Running"
-          service:
-            label: "foo=bar"
-            field: "metadata.status=Running"
-          endpoints:
-            label: "foo=bar"
-            field: "metadata.status=Running"
+        - role: "pod"
+          label: "foo=bar"
+          field: "metadata.status=Running"
+        - role: "service"
+          label: "foo=bar"
+          field: "metadata.status=Running"
+        - role: "endpoints"
+          label: "foo=bar"
+          field: "metadata.status=Running"

config/testdata/kubernetes_selectors_incorrect_selector.bad.yml

@@ -0,0 +1,7 @@
+scrape_configs:
+- job_name: prometheus
+  kubernetes_sd_configs:
+  - role: endpoints
+    selectors:
+    - role: "pod"
+      field: "metadata.status-Running"

config/testdata/kubernetes_selectors_ingress.bad.yml

@@ -3,6 +3,6 @@ scrape_configs:
     kubernetes_sd_configs:
       - role: ingress
         selectors:
-          node:
+          - role:  "node"
             label: "foo=bar"
             field: "metadata.status=Running"

config/testdata/kubernetes_selectors_ingress.good.yml

@@ -3,6 +3,6 @@ scrape_configs:
     kubernetes_sd_configs:
       - role: ingress
         selectors:
-          ingress:
+          - role:  "ingress"
             label: "foo=bar"
             field: "metadata.status=Running"

config/testdata/kubernetes_selectors_node.bad.yml

@@ -3,6 +3,6 @@ scrape_configs:
     kubernetes_sd_configs:
       - role: node
         selectors:
-          pod:
+          - role:  "pod"
             label: "foo=bar"
             field: "metadata.status=Running"

config/testdata/kubernetes_selectors_node.good.yml

@@ -3,6 +3,6 @@ scrape_configs:
     kubernetes_sd_configs:
       - role: node
         selectors:
-          node:
+          - role:  "node"
             label: "foo=bar"
             field: "metadata.status=Running"

config/testdata/kubernetes_selectors_pod.bad.yml

@@ -3,6 +3,6 @@ scrape_configs:
     kubernetes_sd_configs:
       - role: pod
         selectors:
-          node:
+          - role:  "node"
             label: "foo=bar"
             field: "metadata.status=Running"

config/testdata/kubernetes_selectors_pod.good.yml

@@ -3,6 +3,6 @@ scrape_configs:
     kubernetes_sd_configs:
       - role: pod
         selectors:
-          pod:
+          - role:  "pod"
             label: "foo=bar"
             field: "metadata.status=Running"

config/testdata/kubernetes_selectors_service.bad.yml

@@ -3,6 +3,6 @@ scrape_configs:
     kubernetes_sd_configs:
       - role: service
         selectors:
-          pod:
+          - role:  "pod"
             label: "foo=bar"
             field: "metadata.status=Running"

config/testdata/kubernetes_selectors_service.good.yml

@@ -3,6 +3,6 @@ scrape_configs:
     kubernetes_sd_configs:
       - role: service
         selectors:
-          service:
+          - role:  "service"
             label: "foo=bar"
             field: "metadata.status=Running"

discovery/kubernetes/kubernetes.go

@@ -16,6 +16,7 @@ package kubernetes
 import (
 	"context"
 	"reflect"
+	"strings"
 	"sync"
 	"time"
 
@@ -28,6 +29,7 @@ import (
 	apiv1 "k8s.io/api/core/v1"
 	extensionsv1beta1 "k8s.io/api/extensions/v1beta1"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/apimachinery/pkg/fields"
 	"k8s.io/apimachinery/pkg/runtime"
 	"k8s.io/apimachinery/pkg/watch"
 	"k8s.io/client-go/kubernetes"
@@ -91,22 +93,28 @@ type SDConfig struct {
 	Role               Role                         `yaml:"role"`
 	HTTPClientConfig   config_util.HTTPClientConfig `yaml:",inline"`
 	NamespaceDiscovery NamespaceDiscovery           `yaml:"namespaces,omitempty"`
-	Selectors          RoleSelectorConfig           `yaml:"selectors,omitempty"`
+	Selectors          []SelectorConfig             `yaml:"selectors,omitempty"`
 }
 
-type RoleSelectorConfig struct {
-	Node      ResourceSelectorConfig `yaml:"node,omitempty"`
-	Pod       ResourceSelectorConfig `yaml:"pod,omitempty"`
-	Service   ResourceSelectorConfig `yaml:"service,omitempty"`
-	Endpoints ResourceSelectorConfig `yaml:"endpoints,omitempty"`
-	Ingress   ResourceSelectorConfig `yaml:"ingress,omitempty"`
+type roleSelector struct {
+	node      resourceSelector
+	pod       resourceSelector
+	service   resourceSelector
+	endpoints resourceSelector
+	ingress   resourceSelector
 }
 
-type ResourceSelectorConfig struct {
+type SelectorConfig struct {
+	Role  Role   `yaml:"role,omitempty"`
 	Label string `yaml:"label,omitempty"`
 	Field string `yaml:"field,omitempty"`
 }
 
+type resourceSelector struct {
+	label string
+	field string
+}
+
 // UnmarshalYAML implements the yaml.Unmarshaler interface.
 func (c *SDConfig) UnmarshalYAML(unmarshal func(interface{}) error) error {
 	*c = SDConfig{}
@@ -115,6 +123,9 @@ func (c *SDConfig) UnmarshalYAML(unmarshal func(interface{}) error) error {
 	if err != nil {
 		return err
 	}
+	if c.Role == "" {
+		return errors.Errorf("role missing (one of: pod, service, endpoints, node, ingress)")
+	}
 	err = c.HTTPClientConfig.Validate()
 	if err != nil {
 		return err
@@ -122,29 +133,45 @@ func (c *SDConfig) UnmarshalYAML(unmarshal func(interface{}) error) error {
 	if c.APIServer.URL == nil && !reflect.DeepEqual(c.HTTPClientConfig, config_util.HTTPClientConfig{}) {
 		return errors.Errorf("to use custom HTTP client configuration please provide the 'api_server' URL explicitly")
 	}
-	switch c.Role {
-	case "pod":
-		if len(c.Selectors.Service.Field) > 0 || len(c.Selectors.Endpoints.Field) > 0 || len(c.Selectors.Ingress.Field) > 0 || len(c.Selectors.Node.Field) > 0 {
-			return errors.Errorf("pod role supports only pod selectors")
+
+	foundSelectorRoles := make(map[Role]struct{})
+	allowedSelectors := map[Role][]string{
+		RolePod:      {string(RolePod)},
+		RoleService:  {string(RoleService)},
+		RoleEndpoint: {string(RolePod), string(RoleService), string(RoleEndpoint)},
+		RoleNode:     {string(RoleNode)},
+		RoleIngress:  {string(RoleIngress)},
+	}
+
+	for _, selector := range c.Selectors {
+		if _, ok := foundSelectorRoles[selector.Role]; ok {
+			return errors.Errorf("duplicated selector role: %s", selector.Role)
 		}
-	case "service":
-		if len(c.Selectors.Pod.Field) > 0 || len(c.Selectors.Endpoints.Field) > 0 || len(c.Selectors.Ingress.Field) > 0 || len(c.Selectors.Node.Field) > 0 {
-			return errors.Errorf("service role supports only service selectors")
+		foundSelectorRoles[selector.Role] = struct{}{}
+
+		if _, ok := allowedSelectors[c.Role]; !ok {
+			return errors.Errorf("invalid role: %q, expecting one of: pod, service, endpoints, node or ingress", c.Role)
 		}
-	case "endpoints":
-		if len(c.Selectors.Ingress.Field) > 0 || len(c.Selectors.Node.Field) > 0 {
-			return errors.Errorf("endpoints role supports only pod, service and endpoints selectors")
+		var allowed bool
+		for _, role := range allowedSelectors[c.Role] {
+			if role == string(selector.Role) {
+				allowed = true
+				break
+			}
 		}
-	case "node":
-		if len(c.Selectors.Service.Field) > 0 || len(c.Selectors.Endpoints.Field) > 0 || len(c.Selectors.Ingress.Field) > 0 || len(c.Selectors.Pod.Field) > 0 {
-			return errors.Errorf("node role supports only node selectors")
+
+		if !allowed {
+			return errors.Errorf("%s role supports only %s selectors", c.Role, strings.Join(allowedSelectors[c.Role], ", "))
 		}
-	case "ingress":
-		if len(c.Selectors.Service.Field) > 0 || len(c.Selectors.Endpoints.Field) > 0 || len(c.Selectors.Node.Field) > 0 || len(c.Selectors.Pod.Field) > 0 {
-			return errors.Errorf("ingress role supports only ingress selectors")
+
+		_, err := fields.ParseSelector(selector.Field)
+		if err != nil {
+			return err
+		}
+		_, err = fields.ParseSelector(selector.Label)
+		if err != nil {
+			return err
 		}
-	default:
-		return errors.Errorf("role missing (one of: pod, service, endpoints, node, ingress)")
 	}
 	return nil
 }
@@ -196,7 +223,7 @@ type Discovery struct {
 	logger             log.Logger
 	namespaceDiscovery *NamespaceDiscovery
 	discoverers        []discoverer
-	selectors          RoleSelectorConfig
+	selectors          roleSelector
 }
 
 func (d *Discovery) getNamespaces() []string {
@@ -247,10 +274,34 @@ func New(l log.Logger, conf *SDConfig) (*Discovery, error) {
 		role:               conf.Role,
 		namespaceDiscovery: &conf.NamespaceDiscovery,
 		discoverers:        make([]discoverer, 0),
-		selectors:          conf.Selectors,
+		selectors:          mapSelector(conf.Selectors),
 	}, nil
 }
 
+func mapSelector(rawSelector []SelectorConfig) roleSelector {
+	rs := roleSelector{}
+	for _, resourceSelectorRaw := range rawSelector {
+		switch resourceSelectorRaw.Role {
+		case RoleEndpoint:
+			rs.endpoints.field = resourceSelectorRaw.Field
+			rs.endpoints.label = resourceSelectorRaw.Label
+		case RoleIngress:
+			rs.ingress.field = resourceSelectorRaw.Field
+			rs.ingress.label = resourceSelectorRaw.Label
+		case RoleNode:
+			rs.node.field = resourceSelectorRaw.Field
+			rs.node.label = resourceSelectorRaw.Label
+		case RolePod:
+			rs.pod.field = resourceSelectorRaw.Field
+			rs.pod.label = resourceSelectorRaw.Label
+		case RoleService:
+			rs.service.field = resourceSelectorRaw.Field
+			rs.service.label = resourceSelectorRaw.Label
+		}
+	}
+	return rs
+}
+
 const resyncPeriod = 10 * time.Minute
 
 // Run implements the discoverer interface.
@@ -264,39 +315,39 @@ func (d *Discovery) Run(ctx context.Context, ch chan<- []*targetgroup.Group) {
 			e := d.client.CoreV1().Endpoints(namespace)
 			elw := &cache.ListWatch{
 				ListFunc: func(options metav1.ListOptions) (runtime.Object, error) {
-					options.FieldSelector = d.selectors.Endpoints.Field
-					options.LabelSelector = d.selectors.Endpoints.Label
+					options.FieldSelector = d.selectors.endpoints.field
+					options.LabelSelector = d.selectors.endpoints.label
 					return e.List(options)
 				},
 				WatchFunc: func(options metav1.ListOptions) (watch.Interface, error) {
-					options.FieldSelector = d.selectors.Endpoints.Field
-					options.LabelSelector = d.selectors.Endpoints.Label
+					options.FieldSelector = d.selectors.endpoints.field
+					options.LabelSelector = d.selectors.endpoints.label
 					return e.Watch(options)
 				},
 			}
 			s := d.client.CoreV1().Services(namespace)
 			slw := &cache.ListWatch{
 				ListFunc: func(options metav1.ListOptions) (runtime.Object, error) {
-					options.FieldSelector = d.selectors.Service.Field
-					options.LabelSelector = d.selectors.Service.Label
+					options.FieldSelector = d.selectors.service.field
+					options.LabelSelector = d.selectors.service.label
 					return s.List(options)
 				},
 				WatchFunc: func(options metav1.ListOptions) (watch.Interface, error) {
-					options.FieldSelector = d.selectors.Service.Field
-					options.LabelSelector = d.selectors.Service.Label
+					options.FieldSelector = d.selectors.service.field
+					options.LabelSelector = d.selectors.service.label
 					return s.Watch(options)
 				},
 			}
 			p := d.client.CoreV1().Pods(namespace)
 			plw := &cache.ListWatch{
 				ListFunc: func(options metav1.ListOptions) (runtime.Object, error) {
-					options.FieldSelector = d.selectors.Pod.Field
-					options.LabelSelector = d.selectors.Pod.Label
+					options.FieldSelector = d.selectors.pod.field
+					options.LabelSelector = d.selectors.pod.label
 					return p.List(options)
 				},
 				WatchFunc: func(options metav1.ListOptions) (watch.Interface, error) {
-					options.FieldSelector = d.selectors.Pod.Field
-					options.LabelSelector = d.selectors.Pod.Label
+					options.FieldSelector = d.selectors.pod.field
+					options.LabelSelector = d.selectors.pod.label
 					return p.Watch(options)
 				},
 			}
@@ -316,13 +367,13 @@ func (d *Discovery) Run(ctx context.Context, ch chan<- []*targetgroup.Group) {
 			p := d.client.CoreV1().Pods(namespace)
 			plw := &cache.ListWatch{
 				ListFunc: func(options metav1.ListOptions) (runtime.Object, error) {
-					options.FieldSelector = d.selectors.Pod.Field
-					options.LabelSelector = d.selectors.Pod.Label
+					options.FieldSelector = d.selectors.pod.field
+					options.LabelSelector = d.selectors.pod.label
 					return p.List(options)
 				},
 				WatchFunc: func(options metav1.ListOptions) (watch.Interface, error) {
-					options.FieldSelector = d.selectors.Pod.Field
-					options.LabelSelector = d.selectors.Pod.Label
+					options.FieldSelector = d.selectors.pod.field
+					options.LabelSelector = d.selectors.pod.label
 					return p.Watch(options)
 				},
 			}
@@ -338,13 +389,13 @@ func (d *Discovery) Run(ctx context.Context, ch chan<- []*targetgroup.Group) {
 			s := d.client.CoreV1().Services(namespace)
 			slw := &cache.ListWatch{
 				ListFunc: func(options metav1.ListOptions) (runtime.Object, error) {
-					options.FieldSelector = d.selectors.Service.Field
-					options.LabelSelector = d.selectors.Service.Label
+					options.FieldSelector = d.selectors.service.field
+					options.LabelSelector = d.selectors.service.label
 					return s.List(options)
 				},
 				WatchFunc: func(options metav1.ListOptions) (watch.Interface, error) {
-					options.FieldSelector = d.selectors.Service.Field
-					options.LabelSelector = d.selectors.Service.Label
+					options.FieldSelector = d.selectors.service.field
+					options.LabelSelector = d.selectors.service.label
 					return s.Watch(options)
 				},
 			}
@@ -360,13 +411,13 @@ func (d *Discovery) Run(ctx context.Context, ch chan<- []*targetgroup.Group) {
 			i := d.client.ExtensionsV1beta1().Ingresses(namespace)
 			ilw := &cache.ListWatch{
 				ListFunc: func(options metav1.ListOptions) (runtime.Object, error) {
-					options.FieldSelector = d.selectors.Ingress.Field
-					options.LabelSelector = d.selectors.Ingress.Label
+					options.FieldSelector = d.selectors.ingress.field
+					options.LabelSelector = d.selectors.ingress.label
 					return i.List(options)
 				},
 				WatchFunc: func(options metav1.ListOptions) (watch.Interface, error) {
-					options.FieldSelector = d.selectors.Ingress.Field
-					options.LabelSelector = d.selectors.Ingress.Label
+					options.FieldSelector = d.selectors.ingress.field
+					options.LabelSelector = d.selectors.ingress.label
 					return i.Watch(options)
 				},
 			}
@@ -380,13 +431,13 @@ func (d *Discovery) Run(ctx context.Context, ch chan<- []*targetgroup.Group) {
 	case RoleNode:
 		nlw := &cache.ListWatch{
 			ListFunc: func(options metav1.ListOptions) (runtime.Object, error) {
-				options.FieldSelector = d.selectors.Node.Field
-				options.LabelSelector = d.selectors.Node.Label
+				options.FieldSelector = d.selectors.node.field
+				options.LabelSelector = d.selectors.node.label
 				return d.client.CoreV1().Nodes().List(options)
 			},
 			WatchFunc: func(options metav1.ListOptions) (watch.Interface, error) {
-				options.FieldSelector = d.selectors.Node.Field
-				options.LabelSelector = d.selectors.Node.Label
+				options.FieldSelector = d.selectors.node.field
+				options.LabelSelector = d.selectors.node.label
 				return d.client.CoreV1().Nodes().Watch(options)
 			},
 		}

docs/configuration/configuration.md

@@ -860,10 +860,17 @@ namespaces:
 # and https://kubernetes.io/docs/concepts/overview/working-with-objects/labels/ to learn more about the possible 
 # filters that can be used. Endpoints role supports pod, service and endpoints selectors, other roles
 # only support selectors matching the role itself (e.g. node role can only contain node selectors).
-selectors:
-  <role>:
+
+# Note: When making decision about using field/label selector make sure that this 
+# is the best approach - it will prevent Prometheus from reusing single list/watch
+# for all scrape configs. This might result in a bigger load on the Kubernetes API,
+# because per each selector combination there will be additional LIST/WATCH. On the other hand,
+# if you just want to monitor small subset of pods in large cluster it's recommended to use selectors.
+# Decision, if selectors should be used or not depends on the particular situation.
+[ selectors:
+  [ - role: <role>  
     [ label: <string> ]
-    [ field: <string> ]
+    [ field: <string> ] ]]
 ```
 
 Where `<role>` must be `endpoints`, `service`, `pod`, `node`, or