Merge #4126

4126: Make the experimental route /metrics activable via HTTP r=dureuill a=braddotcoffee

# Pull Request

## Related issue
Closes #4086

## What does this PR do?
- [x] Make `/metrics` available via HTTP as described in #4086 
- [x] The users can still launch Meilisearch using the `--experimental-enable-metrics` flag.
- [x] If the flag `--experimental-enable-metrics` is activated, a call to the `GET /experimental-features` route right after the launch will show `"metrics": true` even if the user has not called the `PATCH /experimental-features` route yet.
- [x] Even if the --experimental-enable-metrics flag is present at launch, calling the `PATCH /experimental-features` route with `"metrics": false` disables the experimental feature.
- [x] Update the spec
    - I was unable to find docs in this repository to update about the `/experimental-features` endpoint. I'll happily update if you point me in the right direction!

## PR checklist
Please check if your PR fulfills the following requirements:
- [x] Does this PR fix an existing issue, or have you listed the changes applied in the PR description (and why they are needed)?
- [x] Have you read the contributing guidelines?
- [x] Have you made sure that the title is accurate and descriptive of the changes?

Co-authored-by: bwbonanno <bradfordbonanno@gmail.com>
Co-authored-by: Louis Dureuil <louis@meilisearch.com>

index-scheduler/src/batch.rs

@@ -896,7 +896,7 @@ impl IndexScheduler {
                 })?;
 
                 // 4. Dump experimental feature settings
-                let features = self.features()?.runtime_features();
+                let features = self.features().runtime_features();
                 dump.create_experimental_features(features)?;
 
                 let dump_uid = started_at.format(format_description!(

index-scheduler/src/features.rs

@@ -1,6 +1,8 @@
+use std::sync::{Arc, RwLock};
+
 use meilisearch_types::features::{InstanceTogglableFeatures, RuntimeTogglableFeatures};
 use meilisearch_types::heed::types::{SerdeJson, Str};
-use meilisearch_types::heed::{Database, Env, RoTxn, RwTxn};
+use meilisearch_types::heed::{Database, Env, RwTxn};
 
 use crate::error::FeatureNotEnabledError;
 use crate::Result;
@@ -9,20 +11,19 @@ const EXPERIMENTAL_FEATURES: &str = "experimental-features";
 
 #[derive(Clone)]
 pub(crate) struct FeatureData {
-    runtime: Database<Str, SerdeJson<RuntimeTogglableFeatures>>,
-    instance: InstanceTogglableFeatures,
+    persisted: Database<Str, SerdeJson<RuntimeTogglableFeatures>>,
+    runtime: Arc<RwLock<RuntimeTogglableFeatures>>,
 }
 
 #[derive(Debug, Clone, Copy)]
 pub struct RoFeatures {
     runtime: RuntimeTogglableFeatures,
-    instance: InstanceTogglableFeatures,
 }
 
 impl RoFeatures {
-    fn new(txn: RoTxn<'_>, data: &FeatureData) -> Result<Self> {
-        let runtime = data.runtime_features(txn)?;
-        Ok(Self { runtime, instance: data.instance })
+    fn new(data: &FeatureData) -> Self {
+        let runtime = data.runtime_features();
+        Self { runtime }
     }
 
     pub fn runtime_features(&self) -> RuntimeTogglableFeatures {
@@ -43,7 +44,7 @@ impl RoFeatures {
     }
 
     pub fn check_metrics(&self) -> Result<()> {
-        if self.instance.metrics {
+        if self.runtime.metrics {
             Ok(())
         } else {
             Err(FeatureNotEnabledError {
@@ -85,10 +86,18 @@ impl RoFeatures {
 impl FeatureData {
     pub fn new(env: &Env, instance_features: InstanceTogglableFeatures) -> Result<Self> {
         let mut wtxn = env.write_txn()?;
-        let runtime_features = env.create_database(&mut wtxn, Some(EXPERIMENTAL_FEATURES))?;
+        let runtime_features_db = env.create_database(&mut wtxn, Some(EXPERIMENTAL_FEATURES))?;
         wtxn.commit()?;
 
-        Ok(Self { runtime: runtime_features, instance: instance_features })
+        let txn = env.read_txn()?;
+        let persisted_features: RuntimeTogglableFeatures =
+            runtime_features_db.get(&txn, EXPERIMENTAL_FEATURES)?.unwrap_or_default();
+        let runtime = Arc::new(RwLock::new(RuntimeTogglableFeatures {
+            metrics: instance_features.metrics || persisted_features.metrics,
+            ..persisted_features
+        }));
+
+        Ok(Self { persisted: runtime_features_db, runtime })
     }
 
     pub fn put_runtime_features(
@@ -96,16 +105,25 @@ impl FeatureData {
         mut wtxn: RwTxn,
         features: RuntimeTogglableFeatures,
     ) -> Result<()> {
-        self.runtime.put(&mut wtxn, EXPERIMENTAL_FEATURES, &features)?;
+        self.persisted.put(&mut wtxn, EXPERIMENTAL_FEATURES, &features)?;
         wtxn.commit()?;
+
+        // safe to unwrap, the lock will only fail if:
+        // 1. requested by the same thread concurrently -> it is called and released in methods that don't call each other
+        // 2. there's a panic while the thread is held -> it is only used for an assignment here.
+        let mut toggled_features = self.runtime.write().unwrap();
+        *toggled_features = features;
         Ok(())
     }
 
-    fn runtime_features(&self, txn: RoTxn) -> Result<RuntimeTogglableFeatures> {
-        Ok(self.runtime.get(&txn, EXPERIMENTAL_FEATURES)?.unwrap_or_default())
+    fn runtime_features(&self) -> RuntimeTogglableFeatures {
+        // sound to unwrap, the lock will only fail if:
+        // 1. requested by the same thread concurrently -> it is called and released in methods that don't call each other
+        // 2. there's a panic while the thread is held -> it is only used for copying the data here
+        *self.runtime.read().unwrap()
     }
 
-    pub fn features(&self, txn: RoTxn) -> Result<RoFeatures> {
-        RoFeatures::new(txn, self)
+    pub fn features(&self) -> RoFeatures {
+        RoFeatures::new(self)
     }
 }

index-scheduler/src/lib.rs

@@ -579,13 +579,7 @@ impl IndexScheduler {
                 run.wake_up.wait();
 
                 loop {
-                    let puffin_enabled = match run.features() {
-                        Ok(features) => features.check_puffin().is_ok(),
-                        Err(e) => {
-                            log::error!("{e}");
-                            continue;
-                        }
-                    };
+                    let puffin_enabled = run.features().check_puffin().is_ok();
                     puffin::set_scopes_on(puffin_enabled);
                     puffin::GlobalProfiler::lock().new_frame();
 
@@ -1299,9 +1293,8 @@ impl IndexScheduler {
         Ok(IndexStats { is_indexing, inner_stats: index_stats })
     }
 
-    pub fn features(&self) -> Result<RoFeatures> {
-        let rtxn = self.read_txn()?;
-        self.features.features(rtxn)
+    pub fn features(&self) -> RoFeatures {
+        self.features.features()
     }
 
     pub fn put_runtime_features(&self, features: RuntimeTogglableFeatures) -> Result<()> {

meilisearch-types/src/features.rs

@@ -5,6 +5,7 @@ use serde::{Deserialize, Serialize};
 pub struct RuntimeTogglableFeatures {
     pub score_details: bool,
     pub vector_store: bool,
+    pub metrics: bool,
     pub export_puffin_reports: bool,
 }
 

meilisearch/src/lib.rs

@@ -114,10 +114,7 @@ pub fn create_app(
         .configure(routes::configure)
         .configure(|s| dashboard(s, enable_dashboard));
 
-    let app = app.wrap(actix_web::middleware::Condition::new(
-        opt.experimental_enable_metrics,
-        middleware::RouteMetrics,
-    ));
+    let app = app.wrap(middleware::RouteMetrics);
     app.wrap(
         Cors::default()
             .send_wildcard()

meilisearch/src/middleware.rs

@@ -3,8 +3,10 @@
 use std::future::{ready, Ready};
 
 use actix_web::dev::{self, Service, ServiceRequest, ServiceResponse, Transform};
+use actix_web::web::Data;
 use actix_web::Error;
 use futures_util::future::LocalBoxFuture;
+use index_scheduler::IndexScheduler;
 use prometheus::HistogramTimer;
 
 pub struct RouteMetrics;
@@ -47,6 +49,13 @@ where
 
     fn call(&self, req: ServiceRequest) -> Self::Future {
         let mut histogram_timer: Option<HistogramTimer> = None;
+
+        // calling unwrap here is safe because index scheduler is added to app data while creating actix app.
+        // also, the tests will fail if this is not present.
+        let index_scheduler = req.app_data::<Data<IndexScheduler>>().unwrap();
+        let features = index_scheduler.features();
+
+        if features.check_metrics().is_ok() {
             let request_path = req.path();
             let is_registered_resource = req.resource_map().has_resource(request_path);
             if is_registered_resource {
@@ -60,6 +69,7 @@ where
                     .with_label_values(&[&request_method, request_path])
                     .inc();
             }
+        };
 
         let fut = self.service.call(req);
 

meilisearch/src/routes/features.rs

@@ -29,12 +29,12 @@ async fn get_features(
     >,
     req: HttpRequest,
     analytics: Data<dyn Analytics>,
-) -> Result<HttpResponse, ResponseError> {
-    let features = index_scheduler.features()?;
+) -> HttpResponse {
+    let features = index_scheduler.features();
 
     analytics.publish("Experimental features Seen".to_string(), json!(null), Some(&req));
     debug!("returns: {:?}", features.runtime_features());
-    Ok(HttpResponse::Ok().json(features.runtime_features()))
+    HttpResponse::Ok().json(features.runtime_features())
 }
 
 #[derive(Debug, Deserr)]
@@ -45,6 +45,8 @@ pub struct RuntimeTogglableFeatures {
     #[deserr(default)]
     pub vector_store: Option<bool>,
     #[deserr(default)]
+    pub metrics: Option<bool>,
+    #[deserr(default)]
     pub export_puffin_reports: Option<bool>,
 }
 
@@ -57,12 +59,13 @@ async fn patch_features(
     req: HttpRequest,
     analytics: Data<dyn Analytics>,
 ) -> Result<HttpResponse, ResponseError> {
-    let features = index_scheduler.features()?;
+    let features = index_scheduler.features();
 
     let old_features = features.runtime_features();
     let new_features = meilisearch_types::features::RuntimeTogglableFeatures {
         score_details: new_features.0.score_details.unwrap_or(old_features.score_details),
         vector_store: new_features.0.vector_store.unwrap_or(old_features.vector_store),
+        metrics: new_features.0.metrics.unwrap_or(old_features.metrics),
         export_puffin_reports: new_features
             .0
             .export_puffin_reports
@@ -75,6 +78,7 @@ async fn patch_features(
     let meilisearch_types::features::RuntimeTogglableFeatures {
         score_details,
         vector_store,
+        metrics,
         export_puffin_reports,
     } = new_features;
 
@@ -83,6 +87,7 @@ async fn patch_features(
         json!({
             "score_details": score_details,
             "vector_store": vector_store,
+            "metrics": metrics,
             "export_puffin_reports": export_puffin_reports,
         }),
         Some(&req),

meilisearch/src/routes/indexes/facet_search.rs

@@ -68,7 +68,7 @@ pub async fn search(
     }
 
     let index = index_scheduler.index(&index_uid)?;
-    let features = index_scheduler.features()?;
+    let features = index_scheduler.features();
     let search_result = tokio::task::spawn_blocking(move || {
         perform_facet_search(&index, search_query, facet_query, facet_name, features)
     })

meilisearch/src/routes/indexes/search.rs

@@ -157,7 +157,7 @@ pub async fn search_with_url_query(
     let mut aggregate = SearchAggregator::from_query(&query, &req);
 
     let index = index_scheduler.index(&index_uid)?;
-    let features = index_scheduler.features()?;
+    let features = index_scheduler.features();
     let search_result =
         tokio::task::spawn_blocking(move || perform_search(&index, query, features)).await?;
     if let Ok(ref search_result) = search_result {
@@ -192,7 +192,7 @@ pub async fn search_with_post(
 
     let index = index_scheduler.index(&index_uid)?;
 
-    let features = index_scheduler.features()?;
+    let features = index_scheduler.features();
     let search_result =
         tokio::task::spawn_blocking(move || perform_search(&index, query, features)).await?;
     if let Ok(ref search_result) = search_result {

meilisearch/src/routes/metrics.rs

@@ -19,7 +19,7 @@ pub async fn get_metrics(
     index_scheduler: GuardedData<ActionPolicy<{ actions::METRICS_GET }>, Data<IndexScheduler>>,
     auth_controller: Data<AuthController>,
 ) -> Result<HttpResponse, ResponseError> {
-    index_scheduler.features()?.check_metrics()?;
+    index_scheduler.features().check_metrics()?;
     let auth_filters = index_scheduler.filters();
     if !auth_filters.all_indexes_authorized() {
         let mut error = ResponseError::from(AuthenticationError::InvalidToken);

meilisearch/src/routes/multi_search.rs

@@ -41,7 +41,7 @@ pub async fn multi_search_with_post(
     let queries = params.into_inner().queries;
 
     let mut multi_aggregate = MultiSearchAggregator::from_queries(&queries, &req);
-    let features = index_scheduler.features()?;
+    let features = index_scheduler.features();
 
     // Explicitly expect a `(ResponseError, usize)` for the error type rather than `ResponseError` only,
     // so that `?` doesn't work if it doesn't use `with_index`, ensuring that it is not forgotten in case of code

meilisearch/tests/auth/authorization.rs

@@ -2,10 +2,12 @@ use std::collections::{HashMap, HashSet};
 
 use ::time::format_description::well_known::Rfc3339;
 use maplit::{hashmap, hashset};
+use meilisearch::Opt;
 use once_cell::sync::Lazy;
+use tempfile::TempDir;
 use time::{Duration, OffsetDateTime};
 
-use crate::common::{Server, Value};
+use crate::common::{default_settings, Server, Value};
 use crate::json;
 
 pub static AUTHORIZATIONS: Lazy<HashMap<(&'static str, &'static str), HashSet<&'static str>>> =
@@ -195,7 +197,9 @@ async fn access_authorized_master_key() {
 
 #[actix_rt::test]
 async fn access_authorized_restricted_index() {
-    let mut server = Server::new_auth().await;
+    let dir = TempDir::new().unwrap();
+    let enable_metrics = Opt { experimental_enable_metrics: true, ..default_settings(dir.path()) };
+    let mut server = Server::new_auth_with_options(enable_metrics, dir).await;
     for ((method, route), actions) in AUTHORIZATIONS.iter() {
         for action in actions {
             // create a new API key letting only the needed action.

meilisearch/tests/common/server.rs

@@ -202,6 +202,10 @@ impl Server {
     pub async fn set_features(&self, value: Value) -> (Value, StatusCode) {
         self.service.patch("/experimental-features", value).await
     }
+
+    pub async fn get_metrics(&self) -> (Value, StatusCode) {
+        self.service.get("/metrics").await
+    }
 }
 
 pub fn default_settings(dir: impl AsRef<Path>) -> Opt {
@@ -221,7 +225,7 @@ pub fn default_settings(dir: impl AsRef<Path>) -> Opt {
             skip_index_budget: true,
             ..Parser::parse_from(None as Option<&str>)
         },
-        experimental_enable_metrics: true,
+        experimental_enable_metrics: false,
         ..Parser::parse_from(None as Option<&str>)
     }
 }

meilisearch/tests/features/mod.rs

@@ -1,4 +1,7 @@
-use crate::common::Server;
+use meilisearch::Opt;
+use tempfile::TempDir;
+
+use crate::common::{default_settings, Server};
 use crate::json;
 
 /// Feature name to test against.
@@ -17,6 +20,7 @@ async fn experimental_features() {
     {
       "scoreDetails": false,
       "vectorStore": false,
+      "metrics": false,
       "exportPuffinReports": false
     }
     "###);
@@ -28,6 +32,7 @@ async fn experimental_features() {
     {
       "scoreDetails": false,
       "vectorStore": true,
+      "metrics": false,
       "exportPuffinReports": false
     }
     "###);
@@ -39,6 +44,7 @@ async fn experimental_features() {
     {
       "scoreDetails": false,
       "vectorStore": true,
+      "metrics": false,
       "exportPuffinReports": false
     }
     "###);
@@ -51,6 +57,7 @@ async fn experimental_features() {
     {
       "scoreDetails": false,
       "vectorStore": true,
+      "metrics": false,
       "exportPuffinReports": false
     }
     "###);
@@ -63,11 +70,72 @@ async fn experimental_features() {
     {
       "scoreDetails": false,
       "vectorStore": true,
+      "metrics": false,
       "exportPuffinReports": false
     }
     "###);
 }
 
+#[actix_rt::test]
+async fn experimental_feature_metrics() {
+    // instance flag for metrics enables metrics at startup
+    let dir = TempDir::new().unwrap();
+    let enable_metrics = Opt { experimental_enable_metrics: true, ..default_settings(dir.path()) };
+    let server = Server::new_with_options(enable_metrics).await.unwrap();
+
+    let (response, code) = server.get_features().await;
+
+    meili_snap::snapshot!(code, @"200 OK");
+    meili_snap::snapshot!(meili_snap::json_string!(response), @r###"
+    {
+      "scoreDetails": false,
+      "vectorStore": false,
+      "metrics": true,
+      "exportPuffinReports": false
+    }
+    "###);
+
+    let (response, code) = server.get_metrics().await;
+    meili_snap::snapshot!(code, @"200 OK");
+
+    // metrics are not returned in json format
+    // so the test server will return null
+    meili_snap::snapshot!(response, @"null");
+
+    // disabling metrics results in invalid request
+    let (response, code) = server.set_features(json!({"metrics": false})).await;
+    meili_snap::snapshot!(code, @"200 OK");
+    meili_snap::snapshot!(response["metrics"], @"false");
+
+    let (response, code) = server.get_metrics().await;
+    meili_snap::snapshot!(code, @"400 Bad Request");
+    meili_snap::snapshot!(meili_snap::json_string!(response), @r###"
+    {
+      "message": "Getting metrics requires enabling the `metrics` experimental feature. See https://github.com/meilisearch/product/discussions/625",
+      "code": "feature_not_enabled",
+      "type": "invalid_request",
+      "link": "https://docs.meilisearch.com/errors#feature_not_enabled"
+    }
+    "###);
+
+    // enabling metrics via HTTP results in valid request
+    let (response, code) = server.set_features(json!({"metrics": true})).await;
+    meili_snap::snapshot!(code, @"200 OK");
+    meili_snap::snapshot!(response["metrics"], @"true");
+
+    let (response, code) = server.get_metrics().await;
+    meili_snap::snapshot!(code, @"200 OK");
+    meili_snap::snapshot!(response, @"null");
+
+    // startup without flag respects persisted metrics value
+    let disable_metrics =
+        Opt { experimental_enable_metrics: false, ..default_settings(dir.path()) };
+    let server_no_flag = Server::new_with_options(disable_metrics).await.unwrap();
+    let (response, code) = server_no_flag.get_metrics().await;
+    meili_snap::snapshot!(code, @"200 OK");
+    meili_snap::snapshot!(response, @"null");
+}
+
 #[actix_rt::test]
 async fn errors() {
     let server = Server::new().await;
@@ -78,7 +146,7 @@ async fn errors() {
     meili_snap::snapshot!(code, @"400 Bad Request");
     meili_snap::snapshot!(meili_snap::json_string!(response), @r###"
     {
-      "message": "Unknown field `NotAFeature`: expected one of `scoreDetails`, `vectorStore`, `exportPuffinReports`",
+      "message": "Unknown field `NotAFeature`: expected one of `scoreDetails`, `vectorStore`, `metrics`, `exportPuffinReports`",
       "code": "bad_request",
       "type": "invalid_request",
       "link": "https://docs.meilisearch.com/errors#bad_request"