uplink api semantics

NEXT_CHANGELOG.md

@@ -50,11 +50,20 @@ By [@bnjjj](https://github.com/bnjjj) in https://github.com/apollographql/router
 
 ## 🐛 Fixes
 
+### Follow directives from Uplink ([Issue #1494](https://github.com/apollographql/router/issues/1494) [Issue #1539](https://github.com/apollographql/router/issues/1539))
+
+The Uplink API returns actionable info in its responses:
+- some error codes indicate an unrecoverable issue, for which the router should not retry the query (example: non-existing graph)
+- it can tell the router when it should retry the query
+
+By [@Geal](https://github.com/Geal) in https://github.com/apollographql/router/pull/2001
+
 ### Fix the rhai SDL print function [Issue #2005](https://github.com/apollographql/router/issues/2005))
 
 A recent change to the way we provide the SDL to plugins broke the rhai SDL print. This fixes it.
 
 By [@fernando-apollo](https://github.com/fernando-apollo) in https://github.com/apollographql/router/pull/2007
+
 ## 🛠 Maintenance
 
 ### Split the configuration file management in multiple modules [Issue #1790](https://github.com/apollographql/router/issues/1790))

apollo-router/src/router.rs

@@ -229,10 +229,7 @@ impl SchemaSource {
                         future::ready(match res {
                             Ok(schema_result) => Some(UpdateSchema(schema_result.schema)),
                             Err(e) => {
-                                tracing::error!(
-                                    "error downloading the schema from Uplink: {:?}",
-                                    e
-                                );
+                                tracing::error!("{}", e);
                                 None
                             }
                         })

apollo-router/src/uplink/mod.rs

@@ -17,6 +17,8 @@ use tokio_stream::wrappers::ReceiverStream;
 use tracing::instrument::WithSubscriber;
 use url::Url;
 
+use self::supergraph_sdl::SupergraphSdlRouterConfigOnFetchError;
+
 const GCP_URL: &str = "https://uplink.api.apollographql.com/graphql";
 const AWS_URL: &str = "https://aws.uplink.api.apollographql.com/graphql";
 
@@ -35,13 +37,6 @@ pub(crate) struct SupergraphSdl;
 pub(crate) enum Error {
     Reqwest(reqwest::Error),
     EmptyResponse,
-    UpLink {
-        // The lint ignores uses in the `Debug` impl, but this is where these fields are useful.
-        #[allow(dead_code)]
-        code: FetchErrorCode,
-        #[allow(dead_code)]
-        message: String,
-    },
 }
 
 impl From<reqwest::Error> for Error {
@@ -60,14 +55,13 @@ pub(crate) fn stream_supergraph(
     api_key: String,
     graph_ref: String,
     urls: Option<Vec<Url>>,
-    interval: Duration,
-) -> impl Stream<Item = Result<Schema, Error>> {
+    mut interval: Duration,
+) -> impl Stream<Item = Result<Schema, String>> {
     let (sender, receiver) = channel(2);
     let _ = tokio::task::spawn(async move {
         let mut composition_id = None;
-
-        let mut interval = tokio::time::interval(interval);
         let mut current_url_idx = 0;
+
         loop {
             match fetch_supergraph(
                 api_key.to_string(),
@@ -91,38 +85,50 @@ pub(crate) fn stream_supergraph(
                         {
                             break;
                         }
+                        // this will truncate the number of seconds to under u64::MAX, which should be
+                        // a large enough delay anyway
+                        interval = Duration::from_secs(schema_config.min_delay_seconds.round() as u64);
                     }
                     supergraph_sdl::SupergraphSdlRouterConfig::Unchanged => {
                         tracing::trace!("schema did not change");
                     }
-                    supergraph_sdl::SupergraphSdlRouterConfig::FetchError(e) => {
-                        if let Some(urls) = &urls {
-                            current_url_idx = (current_url_idx + 1) % urls.len();
+                    supergraph_sdl::SupergraphSdlRouterConfig::FetchError(
+                        SupergraphSdlRouterConfigOnFetchError { code, message },
+                    ) => {
+                        if code == FetchErrorCode::RETRY_LATER {
+                            if let Some(urls) = &urls {
+                                current_url_idx = (current_url_idx + 1) % urls.len();
+                            }
+
+                            if sender
+                            .send(Err(format!("error downloading the schema from Uplink: {}", message)))
+                            .await
+                            .is_err()
+                        {
+                            break;
                         }
-                        if sender
-                            .send(Err(Error::UpLink {
-                                code: e.code,
-                                message: e.message,
-                            }))
+                        } else {
+                            if sender
+                            .send(Err(format!("{:?} error downloading the schema from Uplink, the router will not try again: {}", code, message)))
                             .await
                             .is_err()
                         {
                             break;
                         }
+                            break;
+                        }
                     }
                 },
                 Err(err) => {
                     tracing::error!("error fetching supergraph from Uplink: {:?}", err);
                     if let Some(urls) = &urls {
                         current_url_idx = (current_url_idx + 1) % urls.len();
                     }
-                    if sender.send(Err(err)).await.is_err() {
-                        break;
-                    }
+                    tracing::error!("error downloading the schema from Uplink: {:?}", err);
                 }
             }
 
-            interval.tick().await;
+            tokio::time::sleep(interval).await;
         }
     })
     .with_current_subscriber();

apollo-router/src/uplink/query.graphql

@@ -4,6 +4,7 @@ query SupergraphSdl($apiKey: String!, $graph_ref: String!, $ifAfterId: ID) {
         ... on RouterConfigResult {
             id
             supergraphSdl: supergraphSDL
+            minDelaySeconds
         }
         ... on FetchError {
             code