query-frontend: Added support of auto_discovery for memcached

CHANGELOG.md

@@ -39,6 +39,7 @@ We use *breaking :warning:* to mark changes that are not backward compatible (re
 - [#6605](https://github.com/thanos-io/thanos/pull/6605) Query Frontend: Support vertical sharding binary expression with metric name when no matching labels specified.
 - [#6308](https://github.com/thanos-io/thanos/pull/6308) Ruler: Support configuration flag that allows customizing template for alert message.
 - [#6760](https://github.com/thanos-io/thanos/pull/6760) Query Frontend: Added TLS support in `--query-frontend.downstream-tripper-config` and `--query-frontend.downstream-tripper-config-file`
+- [#7004](https://github.com/thanos-io/thanos/pull/7004) Query Frontend: Support documented auto discovery for memcached
 - [#6749](https://github.com/thanos-io/thanos/pull/6749) Store Gateway: Added `thanos_store_index_cache_fetch_duration_seconds` histogram for tracking latency of fetching data from index cache.
 - [#6690](https://github.com/thanos-io/thanos/pull/6690) Store: *breaking :warning:* Add tenant label to relevant exported metrics. Note that this change may cause some pre-existing dashboard queries to be incorrect due to the added label.
 - [#6530](https://github.com/thanos-io/thanos/pull/6530) / [#6690](https://github.com/thanos-io/thanos/pull/6690) Query: Add command line arguments for configuring tenants and forward tenant information to Store Gateway.

internal/cortex/chunk/cache/memcached_client.go

@@ -19,7 +19,10 @@ import (
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/client_golang/prometheus/promauto"
 	"github.com/sony/gobreaker"
+	"github.com/thanos-io/thanos/pkg/clientconfig"
 	"github.com/thanos-io/thanos/pkg/discovery/dns"
+	memcacheDiscovery "github.com/thanos-io/thanos/pkg/discovery/memcache"
+	"github.com/thanos-io/thanos/pkg/extprom"
 )
 
 // MemcachedClient interface exists for mocking memcacheClient.
@@ -45,7 +48,7 @@ type memcachedClient struct {
 	service  string
 
 	addresses []string
-	provider  *dns.Provider
+	provider  clientconfig.AddressProvider
 
 	cbs        map[ /*address*/ string]*gobreaker.CircuitBreaker
 	cbFailures uint
@@ -68,6 +71,7 @@ type MemcachedClientConfig struct {
 	Host           string        `yaml:"host"`
 	Service        string        `yaml:"service"`
 	Addresses      string        `yaml:"addresses"` // EXPERIMENTAL.
+	AutoDiscovery  bool          `yaml:"auto_discovery"`
 	Timeout        time.Duration `yaml:"timeout"`
 	MaxIdleConns   int           `yaml:"max_idle_conns"`
 	MaxItemSize    int           `yaml:"max_item_size"`
@@ -107,9 +111,19 @@ func NewMemcachedClient(cfg MemcachedClientConfig, name string, r prometheus.Reg
 	client.Timeout = cfg.Timeout
 	client.MaxIdleConns = cfg.MaxIdleConns
 
-	dnsProviderRegisterer := prometheus.WrapRegistererWithPrefix("cortex_", prometheus.WrapRegistererWith(prometheus.Labels{
-		"name": name,
-	}, r))
+	var addressProvider clientconfig.AddressProvider
+	if cfg.AutoDiscovery {
+		addressProvider = memcacheDiscovery.NewProvider(
+			logger,
+			extprom.WrapRegistererWithPrefix("cortex_", r),
+			cfg.Timeout,
+		)
+	} else {
+		dnsProviderRegisterer := prometheus.WrapRegistererWithPrefix("cortex_", prometheus.WrapRegistererWith(prometheus.Labels{
+			"name": name,
+		}, r))
+		addressProvider = dns.NewProvider(logger, dnsProviderRegisterer, dns.GolangResolverType)
+	}
 
 	newClient := &memcachedClient{
 		name:        name,
@@ -118,7 +132,7 @@ func NewMemcachedClient(cfg MemcachedClientConfig, name string, r prometheus.Reg
 		hostname:    cfg.Host,
 		service:     cfg.Service,
 		logger:      logger,
-		provider:    dns.NewProvider(logger, dnsProviderRegisterer, dns.GolangResolverType),
+		provider:    addressProvider,
 		cbs:         make(map[string]*gobreaker.CircuitBreaker),
 		cbFailures:  cfg.CBFailures,
 		cbInterval:  cfg.CBInterval,

pkg/queryfrontend/config.go

@@ -142,6 +142,7 @@ func NewCacheConfig(logger log.Logger, confContentYaml []byte) (*cortexcache.Con
 				Timeout:        config.Memcached.Timeout,
 				MaxIdleConns:   config.Memcached.MaxIdleConnections,
 				Addresses:      strings.Join(config.Memcached.Addresses, ","),
+				AutoDiscovery:  config.Memcached.AutoDiscovery,
 				UpdateInterval: config.Memcached.DNSProviderUpdateInterval,
 				MaxItemSize:    int(config.Memcached.MaxItemSize),
 			},