lib/promscrape/discovery/consulagent: substitute metaPrefix with the __meta_consulagent_ plaintext string

This simplifies future code navigation and search for the specific meta-label starting from __meta_consulagent_* prefix.
For example, `grep __meta_consulagent_namespace` finds the exact place where this label is defined.

Updates https://github.com/VictoriaMetrics/VictoriaMetrics/issues/3953
Updates https://github.com/VictoriaMetrics/VictoriaMetrics/pull/4217

docs/sd_configs.md

@@ -204,23 +204,23 @@ The following meta labels are available on discovered targets during [relabeling
 
 The list of discovered Consul targets is refreshed at the interval, which can be configured via `-promscrape.consulSDCheckInterval` command-line flag.
 
-If you have performance issues with consul_sd_configs on a large cluster, then consider using [consulagent_sd_configs](#consulagent_sd_configs) instead.
+If you have performance issues with `consul_sd_configs` on a large cluster, then consider using [consulagent_sd_configs](#consulagent_sd_configs) instead.
 
 ## consulagent_sd_configs
 
-Consul Agent SD configuration allows retrieving scrape targets from [Consul's Agent API](https://developer.hashicorp.com/consul/api-docs/agent/service).
-When using the Agent API, each running vmagent will only get services registered in the local Consul Agent running on the same node when discovering new targets. 
-It's suitable for huge clusters for which using the [Catalog API](https://developer.hashicorp.com/consul/api-docs/catalog#list-services) would be too slow or resource intensive, 
-in other cases we recommend to use [consul_sd_configs](#consul_sd_configs).
+Consul Agent SD configuration allows retrieving scrape targets from [Consul Agent API](https://developer.hashicorp.com/consul/api-docs/agent/service).
+When using the Agent API, only services registered in the locally running Consul Agent are discovered.
+It is suitable for huge clusters for which using the [Catalog API](https://developer.hashicorp.com/consul/api-docs/catalog#list-services) would be too slow or resource intensive,
+in other cases it is recommended to use [consul_sd_configs](#consul_sd_configs).
 
 Configuration example:
 
 ```yaml
 scrape_configs:
-- job_name: consul
+- job_name: consulagent
   consulagent_sd_configs:
 
-    # server is an optional Consul agent to connect to. By default localhost:8500 is used
+    # server is an optional Consul Agent to connect to. By default localhost:8500 is used
   - server: "localhost:8500"
 
     # token is an optional Consul API token.
@@ -252,12 +252,12 @@ scrape_configs:
     # Individual tags are also available via __meta_consul_tag_<tagname> labels - see below.
     # tag_separator: "..."
 
-    # filter is optional filter for service nodes discovery request. 
+    # filter is optional filter for service nodes discovery request.
     # Replaces tags and node_metadata options.
     # consul supports it since 1.14 version
     # list of supported filters https://developer.hashicorp.com/consul/api-docs/catalog#filtering-1
     # syntax examples https://developer.hashicorp.com/consul/api-docs/features/filtering
-    # filter: "..." 
+    # filter: "..."
 
     # Additional HTTP API client options can be specified here.
     # See https://docs.victoriametrics.com/sd_configs.html#http-api-client-options

lib/promscrape/discovery/consul/agent.go

@@ -29,7 +29,7 @@ type AgentMember struct {
 	Addr string
 }
 
-// ParseAgent parses Consul agent information from bytes.
+// ParseAgent parses Consul agent information from data.
 func ParseAgent(data []byte) (*Agent, error) {
 	var a Agent
 	if err := json.Unmarshal(data, &a); err != nil {

lib/promscrape/discovery/consul/api.go

@@ -144,7 +144,7 @@ func getDatacenter(client *discoveryutils.Client, dc string) (string, error) {
 	}
 	agent, err := GetAgentInfo(client)
 	if err != nil {
-		return "", fmt.Errorf("cannot query consul agent info: %w", err)
+		return "", err
 	}
 	return agent.Config.Datacenter, nil
 }

lib/promscrape/discovery/consulagent/service_node.go

@@ -22,7 +22,6 @@ func getServiceNodesLabels(cfg *apiConfig) []*promutils.Labels {
 }
 
 func appendTargetLabels(sn consul.ServiceNode, ms []*promutils.Labels, serviceName, tagSeparator string, agent *consul.Agent) []*promutils.Labels {
-	const metaPrefix = "__meta_consulagent_"
 	var addr string
 
 	// If the service address is not empty it should be used instead of the node address
@@ -35,30 +34,30 @@ func appendTargetLabels(sn consul.ServiceNode, ms []*promutils.Labels, serviceNa
 
 	m := promutils.NewLabels(16)
 	m.Add("__address__", addr)
-	m.Add(metaPrefix+"address", agent.Member.Addr)
-	m.Add(metaPrefix+"dc", agent.Config.Datacenter)
-	m.Add(metaPrefix+"health", consul.AggregatedStatus(sn.Checks))
-	m.Add(metaPrefix+"namespace", sn.Service.Namespace)
-	m.Add(metaPrefix+"node", agent.Config.NodeName)
-	m.Add(metaPrefix+"service", serviceName)
-	m.Add(metaPrefix+"service_address", sn.Service.Address)
-	m.Add(metaPrefix+"service_id", sn.Service.ID)
-	m.Add(metaPrefix+"service_port", strconv.Itoa(sn.Service.Port))
+	m.Add("__meta_consulagent_address", agent.Member.Addr)
+	m.Add("__meta_consulagent_dc", agent.Config.Datacenter)
+	m.Add("__meta_consulagent_health", consul.AggregatedStatus(sn.Checks))
+	m.Add("__meta_consulagent_namespace", sn.Service.Namespace)
+	m.Add("__meta_consulagent_node", agent.Config.NodeName)
+	m.Add("__meta_consulagent_service", serviceName)
+	m.Add("__meta_consulagent_service_address", sn.Service.Address)
+	m.Add("__meta_consulagent_service_id", sn.Service.ID)
+	m.Add("__meta_consulagent_service_port", strconv.Itoa(sn.Service.Port))
 
-	discoveryutils.AddTagsToLabels(m, sn.Service.Tags, metaPrefix, tagSeparator)
+	discoveryutils.AddTagsToLabels(m, sn.Service.Tags, "__meta_consulagent_", tagSeparator)
 
 	for k, v := range agent.Meta {
-		m.Add(discoveryutils.SanitizeLabelName(metaPrefix+"metadata_"+k), v)
+		m.Add(discoveryutils.SanitizeLabelName("__meta_consulagent_metadata_"+k), v)
 	}
 	for k, v := range sn.Service.Meta {
-		m.Add(discoveryutils.SanitizeLabelName(metaPrefix+"service_metadata_"+k), v)
+		m.Add(discoveryutils.SanitizeLabelName("__meta_consulagent_service_metadata_"+k), v)
 	}
 	for k, v := range sn.Node.TaggedAddresses {
-		m.Add(discoveryutils.SanitizeLabelName(metaPrefix+"tagged_address_"+k), v)
+		m.Add(discoveryutils.SanitizeLabelName("__meta_consulagent_tagged_address_"+k), v)
 	}
 	for k, v := range sn.Service.TaggedAddresses {
 		address := fmt.Sprintf("%s:%d", v.Address, v.Port)
-		m.Add(discoveryutils.SanitizeLabelName(metaPrefix+"tagged_address_"+k), address)
+		m.Add(discoveryutils.SanitizeLabelName("__meta_consulagent_tagged_address_"+k), address)
 	}
 	ms = append(ms, m)
 	return ms