Make conditions in autodiscovery configs optional (elastic#9029)

* Make conditions in autodiscovery configs optional

This change lets users leave the `condition` option undeclared when writing autodiscover configurations. When not declared all configurations will match all events.

* Cleanup

* Fix fmt

* Fix changelog

* Fix failing conditions test

(cherry picked from commit a1bec73)

CHANGELOG.asciidoc

@@ -226,6 +226,7 @@ https://github.com/elastic/beats/compare/v6.4.0...v6.5.0[View commits]
 - Add Beats Central Management {pull}8559[8559]
 - Report configured queue type. {pull}8091[8091]
 - Enable `host` and `cloud` metadata processors by default. {pull}8596[8596]
+- Autodiscovery no longer requires that the `condition` field be set. If left unset all configs will be matched. {pull}9029[9029]
 
 *Filebeat*
 

libbeat/autodiscover/providers/docker/docker.go

@@ -40,7 +40,7 @@ type Provider struct {
 	builders      autodiscover.Builders
 	appenders     autodiscover.Appenders
 	watcher       docker.Watcher
-	templates     *template.Mapper
+	templates     template.Mapper
 	stop          chan interface{}
 	startListener bus.Listener
 	stopListener  bus.Listener

libbeat/autodiscover/providers/jolokia/jolokia.go

@@ -42,7 +42,7 @@ type Provider struct {
 	bus       bus.Bus
 	builders  autodiscover.Builders
 	appenders autodiscover.Appenders
-	templates *template.Mapper
+	templates template.Mapper
 	discovery DiscoveryProber
 }
 

libbeat/autodiscover/providers/kubernetes/kubernetes.go

@@ -41,7 +41,7 @@ type Provider struct {
 	bus       bus.Bus
 	watcher   kubernetes.Watcher
 	metagen   kubernetes.MetaGenerator
-	templates *template.Mapper
+	templates template.Mapper
 	builders  autodiscover.Builders
 	appenders autodiscover.Appenders
 }

libbeat/autodiscover/template/config.go

@@ -42,20 +42,20 @@ type MapperSettings []*struct {
 }
 
 // NewConfigMapper builds a template Mapper from given settings
-func NewConfigMapper(configs MapperSettings) (*Mapper, error) {
-	var mapper Mapper
+func NewConfigMapper(configs MapperSettings) (mapper Mapper, err error) {
 	for _, c := range configs {
-		condition, err := conditions.NewCondition(c.ConditionConfig)
-		if err != nil {
-			return nil, err
+		condMap := &ConditionMap{Configs: c.Configs}
+		if c.ConditionConfig != nil {
+			condMap.Condition, err = conditions.NewCondition(c.ConditionConfig)
+			if err != nil {
+				return nil, err
+			}
 		}
-		mapper = append(mapper, &ConditionMap{
-			Condition: condition,
-			Configs:   c.Configs,
-		})
+
+		mapper = append(mapper, condMap)
 	}
 
-	return &mapper, nil
+	return mapper, nil
 }
 
 // Event adapts MapStr to processors.ValuesMap interface
@@ -71,11 +71,13 @@ func (e Event) GetValue(key string) (interface{}, error) {
 }
 
 // GetConfig returns a matching Config if any, nil otherwise
-func (c *Mapper) GetConfig(event bus.Event) []*common.Config {
+func (c Mapper) GetConfig(event bus.Event) []*common.Config {
 	var result []*common.Config
 
-	for _, mapping := range *c {
-		if mapping.Configs != nil && !mapping.Condition.Check(Event(event)) {
+	for _, mapping := range c {
+		// An empty condition matches everything
+		conditionOk := mapping.Condition == nil || mapping.Condition.Check(Event(event))
+		if mapping.Configs != nil && !conditionOk {
 			continue
 		}
 

libbeat/autodiscover/template/config_test.go

@@ -60,6 +60,16 @@ func TestConfigsMapping(t *testing.T) {
 			},
 			expected: []*common.Config{config},
 		},
+		// No condition
+		{
+			mapping: `
+- config:
+    - correct: config`,
+			event: bus.Event{
+				"foo": 3,
+			},
+			expected: []*common.Config{config},
+		},
 	}
 
 	for _, test := range tests {
@@ -98,5 +108,6 @@ func TestNilConditionConfig(t *testing.T) {
 	}
 
 	_, err = NewConfigMapper(mappings)
-	assert.Error(t, err)
+	assert.NoError(t, err)
+	assert.Nil(t, mappings[0].ConditionConfig)
 }

libbeat/docs/shared-autodiscover.asciidoc

@@ -12,8 +12,8 @@ config file. To enable autodiscover, you specify a list of providers.
 === Providers
 
 Autodiscover providers work by watching for events on the system and translating those events into internal autodiscover
-events with a common format. When you configure the provider, you can use fields from the autodiscover event to set
-conditions that, when met, launch specific configurations.
+events with a common format. When you configure the provider, you can optionally use fields from the autodiscover event
+to set conditions that, when met, launch specific configurations.
 
 On start, {beatname_uc} will scan existing containers and launch the proper configs for them. Then it will watch for new
 start/stop events. This ensures you don't need to worry about state, but only define your desired configs.