[CHANGE] Remote-write: default enable_http2 to false

Remote-write creates several shards to parallelise sending, each with
its own http connection. We do not want them all combined onto one
socket by http2.

Signed-off-by: Bryan Boreham <bjboreham@gmail.com>

CHANGELOG.md

@@ -3,6 +3,7 @@
 ## unreleased
 
 * [CHANGE] Scraping: Remove implicit fallback to the Prometheus text format in case of invalid/missing Content-Type and fail the scrape instead. Add ability to specify a `fallback_scrape_protocol` in the scrape config. #15136
+* [CHANGE] Remote-write: default enable_http2 to false.
 * [ENHANCEMENT] Scraping, rules: handle targets reappearing, or rules moving group, when out-of-order is enabled. #14710 
 - [BUGFIX] PromQL: Fix stddev+stdvar aggregations to always ignore native histograms. #14941
 - [BUGFIX] PromQL: Fix stddev+stdvar aggregations to treat Infinity consistently. #14941

config/config.go

@@ -181,13 +181,18 @@ var (
 		HTTPClientConfig: config.DefaultHTTPClientConfig,
 	}
 
+	DefaultRemoteWriteHTTPClientConfig = config.HTTPClientConfig{
+		FollowRedirects: true,
+		EnableHTTP2:     false,
+	}
+
 	// DefaultRemoteWriteConfig is the default remote write configuration.
 	DefaultRemoteWriteConfig = RemoteWriteConfig{
 		RemoteTimeout:    model.Duration(30 * time.Second),
 		ProtobufMessage:  RemoteWriteProtoMsgV1,
 		QueueConfig:      DefaultQueueConfig,
 		MetadataConfig:   DefaultMetadataConfig,
-		HTTPClientConfig: config.DefaultHTTPClientConfig,
+		HTTPClientConfig: DefaultRemoteWriteHTTPClientConfig,
 	}
 
 	// DefaultQueueConfig is the default remote queue configuration.

docs/configuration/configuration.md

@@ -2889,6 +2889,7 @@ metadata_config:
 
 # HTTP client settings, including authentication methods (such as basic auth and
 # authorization), proxy configurations, TLS options, custom HTTP headers, etc.
+# enable_http2 defaults to false for remote-write.
 [ <http_config> ]
 ```