DNS caching (#1728)

* Allow configuring DNS cache

* Update sample configs

* Fix build errors

* Fix time resolution

* Default 5m

* In seconds

* Use WithDNScache

* Correct field name

* Update go.mod/go.sum to matrix-org/gomatrixserverlib#251

2 files changed, 51 insertions, 2 deletions

diff --git a/setup/base.go b/setup/base.go
index acbf2d35..021dd2b3 100644
--- a/setup/base.go
+++ b/setup/base.go
@@ -73,6 +73,7 @@ type BaseDendrite struct {
 	httpClient             *http.Client
 	Cfg                    *config.Dendrite
 	Caches                 *caching.Caches
+	DNSCache               *gomatrixserverlib.DNSCache
 	//	KafkaConsumer          sarama.Consumer
 	//	KafkaProducer          sarama.SyncProducer
 }
@@ -111,6 +112,20 @@ func NewBaseDendrite(cfg *config.Dendrite, componentName string, useHTTPAPIs boo
 		logrus.WithError(err).Warnf("Failed to create cache")
 	}
 
+	var dnsCache *gomatrixserverlib.DNSCache
+	if cfg.Global.DNSCache.Enabled {
+		lifetime := time.Second * cfg.Global.DNSCache.CacheLifetime
+		dnsCache = gomatrixserverlib.NewDNSCache(
+			cfg.Global.DNSCache.CacheSize,
+			lifetime,
+		)
+		logrus.Infof(
+			"DNS cache enabled (size %d, lifetime %s)",
+			cfg.Global.DNSCache.CacheSize,
+			lifetime,
+		)
+	}
+
 	apiClient := http.Client{
 		Timeout: time.Minute * 10,
 		Transport: &http2.Transport{
@@ -152,6 +167,7 @@ func NewBaseDendrite(cfg *config.Dendrite, componentName string, useHTTPAPIs boo
 		tracerCloser:           closer,
 		Cfg:                    cfg,
 		Caches:                 cache,
+		DNSCache:               dnsCache,
 		PublicClientAPIMux:     mux.NewRouter().SkipClean(true).PathPrefix(httputil.PublicClientPathPrefix).Subrouter().UseEncodedPath(),
 		PublicFederationAPIMux: mux.NewRouter().SkipClean(true).PathPrefix(httputil.PublicFederationPathPrefix).Subrouter().UseEncodedPath(),
 		PublicKeyAPIMux:        mux.NewRouter().SkipClean(true).PathPrefix(httputil.PublicKeyPathPrefix).Subrouter().UseEncodedPath(),
@@ -252,8 +268,12 @@ func (b *BaseDendrite) CreateClient() *gomatrixserverlib.Client {
 	if b.Cfg.Global.DisableFederation {
 		return gomatrixserverlib.NewClientWithTransport(noOpHTTPTransport)
 	}
+	opts := []interface{}{}
+	if b.Cfg.Global.DNSCache.Enabled {
+		opts = append(opts, gomatrixserverlib.WithDNSCache{DNSCache: b.DNSCache})
+	}
 	client := gomatrixserverlib.NewClient(
-		b.Cfg.FederationSender.DisableTLSValidation,
+		b.Cfg.FederationSender.DisableTLSValidation, opts...,
 	)
 	client.SetUserAgent(fmt.Sprintf("Dendrite/%s", internal.VersionString()))
 	return client
@@ -268,9 +288,13 @@ func (b *BaseDendrite) CreateFederationClient() *gomatrixserverlib.FederationCli
 			b.Cfg.FederationSender.DisableTLSValidation, noOpHTTPTransport,
 		)
 	}
+	opts := []interface{}{}
+	if b.Cfg.Global.DNSCache.Enabled {
+		opts = append(opts, gomatrixserverlib.WithDNSCache{DNSCache: b.DNSCache})
+	}
 	client := gomatrixserverlib.NewFederationClientWithTimeout(
 		b.Cfg.Global.ServerName, b.Cfg.Global.KeyID, b.Cfg.Global.PrivateKey,
-		b.Cfg.FederationSender.DisableTLSValidation, time.Minute*5,
+		b.Cfg.FederationSender.DisableTLSValidation, time.Minute*5, opts...,
 	)
 	client.SetUserAgent(fmt.Sprintf("Dendrite/%s", internal.VersionString()))
 	return client
diff --git a/setup/config/config_global.go b/setup/config/config_global.go
index 95652217..d4b068db 100644
--- a/setup/config/config_global.go
+++ b/setup/config/config_global.go
@@ -48,6 +48,9 @@ type Global struct {
 
 	// Metrics configuration
 	Metrics Metrics `yaml:"metrics"`
+
+	// DNS caching options for all outbound HTTP requests
+	DNSCache DNSCacheOptions `yaml:"dns_cache"`
 }
 
 func (c *Global) Defaults() {
@@ -59,6 +62,7 @@ func (c *Global) Defaults() {
 
 	c.Kafka.Defaults()
 	c.Metrics.Defaults()
+	c.DNSCache.Defaults()
 }
 
 func (c *Global) Verify(configErrs *ConfigErrors, isMonolith bool) {
@@ -67,6 +71,7 @@ func (c *Global) Verify(configErrs *ConfigErrors, isMonolith bool) {
 
 	c.Kafka.Verify(configErrs, isMonolith)
 	c.Metrics.Verify(configErrs, isMonolith)
+	c.DNSCache.Verify(configErrs, isMonolith)
 }
 
 type OldVerifyKeys struct {
@@ -140,3 +145,23 @@ func (c DatabaseOptions) MaxOpenConns() int {
 func (c DatabaseOptions) ConnMaxLifetime() time.Duration {
 	return time.Duration(c.ConnMaxLifetimeSeconds) * time.Second
 }
+
+type DNSCacheOptions struct {
+	// Whether the DNS cache is enabled or not
+	Enabled bool `yaml:"enabled"`
+	// How many entries to store in the DNS cache at a given time
+	CacheSize int `yaml:"cache_size"`
+	// How long a cache entry should be considered valid for
+	CacheLifetime time.Duration `yaml:"cache_lifetime"`
+}
+
+func (c *DNSCacheOptions) Defaults() {
+	c.Enabled = false
+	c.CacheSize = 256
+	c.CacheLifetime = time.Minute * 5
+}
+
+func (c *DNSCacheOptions) Verify(configErrs *ConfigErrors, isMonolith bool) {
+	checkPositive(configErrs, "cache_size", int64(c.CacheSize))
+	checkPositive(configErrs, "cache_lifetime", int64(c.CacheLifetime))
+}