API: Promote remote-write-receiver to stable

Since `/api/v1/write` is a mutating endpoint, we should still activate
the remote-write-receiver explicitly. But we should do it in the same
way as the other mutating endpoints, i.e. via a flag
`--web.enable-remote-write-receiver`.

This commit marks the feature flag as deprecated, i.e. it still works
but logs a warning on startup. This enables users to seamlessly
migrate. With the next minor release, we can start ignoring the
feature flag (but still warn a user that is trying to use it).

Signed-off-by: beorn7 <beorn@grafana.com>

cmd/prometheus/main.go

@@ -173,8 +173,8 @@ func (c *flagConfig) setFeatureListOptions(logger log.Logger) error {
 				c.enablePromQLNegativeOffset = true
 				level.Info(logger).Log("msg", "Experimental promql-negative-offset enabled")
 			case "remote-write-receiver":
-				c.web.RemoteWriteReceiver = true
-				level.Info(logger).Log("msg", "Experimental remote-write-receiver enabled")
+				c.web.EnableRemoteWriteReceiver = true
+				level.Warn(logger).Log("msg", "Remote write receiver enabled via feature flag remote-write-receiver. This is DEPRECATED. Use --web.enable-remote-write-receiver.")
 			case "expand-external-labels":
 				c.enableExpandExternalLabels = true
 				level.Info(logger).Log("msg", "Experimental expand-external-labels enabled")
@@ -263,6 +263,9 @@ func main() {
 	a.Flag("web.enable-admin-api", "Enable API endpoints for admin control actions.").
 		Default("false").BoolVar(&cfg.web.EnableAdminAPI)
 
+	a.Flag("web.enable-remote-write-receiver", "Enable API endpoint accepting remote write requests.").
+		Default("false").BoolVar(&cfg.web.EnableRemoteWriteReceiver)
+
 	a.Flag("web.console.templates", "Path to the console template directory, available at /consoles.").
 		Default("consoles").StringVar(&cfg.web.ConsoleTemplatesPath)
 
@@ -381,7 +384,7 @@ func main() {
 	serverOnlyFlag(a, "query.max-samples", "Maximum number of samples a single query can load into memory. Note that queries will fail if they try to load more samples than this into memory, so this also limits the number of samples a query can return.").
 		Default("50000000").IntVar(&cfg.queryMaxSamples)
 
-	a.Flag("enable-feature", "Comma separated feature names to enable. Valid options: agent, exemplar-storage, expand-external-labels, memory-snapshot-on-shutdown, promql-at-modifier, promql-negative-offset, remote-write-receiver, extra-scrape-metrics, new-service-discovery-manager. See https://prometheus.io/docs/prometheus/latest/feature_flags/ for more details.").
+	a.Flag("enable-feature", "Comma separated feature names to enable. Valid options: agent, exemplar-storage, expand-external-labels, memory-snapshot-on-shutdown, promql-at-modifier, promql-negative-offset, remote-write-receiver (DEPRECATED), extra-scrape-metrics, new-service-discovery-manager. See https://prometheus.io/docs/prometheus/latest/feature_flags/ for more details.").
 		Default("").StringsVar(&cfg.featureList)
 
 	promlogflag.AddFlags(a, &cfg.promlogConfig)

docs/feature_flags.md

@@ -46,6 +46,8 @@ More details can be found [here](querying/basics.md#offset-modifier).
 
 The remote write receiver allows Prometheus to accept remote write requests from other Prometheus servers. More details can be found [here](storage.md#overview).
 
+Activating the remote write receiver via a feature flag is deprecated. Use `--web.enable-remote-write-receiver` instead. This feature flag will be ignored in future versions of Prometheus.
+
 ## Exemplars storage
 
 `--enable-feature=exemplar-storage`

docs/querying/api.md

@@ -1145,3 +1145,17 @@ $ curl -XPOST http://localhost:9090/api/v1/admin/tsdb/clean_tombstones
 ```
 
 *New in v2.1 and supports PUT from v2.9*
+
+## Remote Write Receiver
+
+Prometheus can be configured as a receiver for the Prometheus remote write
+protocol. This is not considered an efficient way of ingesting samples. Use it
+with caution for specific low-volume use cases. It is not suitable for
+replacing the ingestion via scraping and turning Prometheus into a push-based
+metrics collection system.
+
+Enable the remote write receiver by setting
+`--web.enable-remote-write-receiver`. When enabled, the remote write receiver
+endpoint is `/api/v1/write`. Find more details [here](../storage.md#overview).
+
+*New in v2.33*

docs/storage.md

@@ -129,7 +129,7 @@ The read and write protocols both use a snappy-compressed protocol buffer encodi
 
 For details on configuring remote storage integrations in Prometheus, see the [remote write](configuration/configuration.md#remote_write) and [remote read](configuration/configuration.md#remote_read) sections of the Prometheus configuration documentation.
 
-The built-in remote write receiver can be enabled by setting the `--enable-feature=remote-write-receiver` command line flag. When enabled, the remote write receiver endpoint is `/api/v1/write`.
+The built-in remote write receiver can be enabled by setting the `--web.enable-remote-write-receiver` command line flag. When enabled, the remote write receiver endpoint is `/api/v1/write`.
 
 For details on the request and response messages, see the [remote storage protocol buffer definitions](https://github.com/prometheus/prometheus/blob/main/prompb/remote.proto).
 

web/web.go

@@ -257,7 +257,7 @@ type Options struct {
 	RemoteReadSampleLimit      int
 	RemoteReadConcurrencyLimit int
 	RemoteReadBytesInFrame     int
-	RemoteWriteReceiver        bool
+	EnableRemoteWriteReceiver  bool
 	IsAgent                    bool
 
 	Gatherer   prometheus.Gatherer
@@ -314,7 +314,7 @@ func New(logger log.Logger, o *Options) *Handler {
 	FactoryRr := func(_ context.Context) api_v1.RulesRetriever { return h.ruleManager }
 
 	var app storage.Appendable
-	if o.RemoteWriteReceiver {
+	if o.EnableRemoteWriteReceiver {
 		app = h.storage
 	}