Uplink connections now reuse reqwest client (#3703)

Previously uplink requests created a new reqwest client each time, this
may cause CPU spikes especially on OSX.

Fixes #3333

<!-- start metadata -->

**Checklist**

Complete the checklist (and note appropriate exceptions) before a final
PR is raised.

- [ ] Changes are compatible[^1]
- [ ] Documentation[^2] completed
- [ ] Performance impact assessed and acceptable
- Tests added and passing[^3]
    - [ ] Unit Tests
    - [ ] Integration Tests
    - [ ] Manual Tests

**Exceptions**

*Note any exceptions here*

**Notes**

[^1]. It may be appropriate to bring upcoming changes to the attention
of other (impacted) groups. Please endeavour to do this before seeking
PR approval. The mechanism for doing this will vary considerably, so use
your judgement as to how and when to do this.
[^2]. Configuration is an important part of many changes. Where
applicable please try to document configuration examples.
[^3]. Tick whichever testing boxes are applicable. If you are adding
Manual Tests:
- please document the manual testing (extensively) in the Exceptions.
- please raise a separate issue to automate the test and label it (or
ask for it to be labeled) as `manual test`

Co-authored-by: bryn <[email protected]>

.changesets/maint_bryn_uplink_client.md

@@ -0,0 +1,6 @@
+### Uplink connections now reuse reqwest client ([Issue #3333](https://github.com/apollographql/router/issues/3333))
+
+Previously uplink requests created a new reqwest client each time, this may cause CPU spikes especially on OSX.
+A single client will now be shared between requests of the same type. 
+
+By [@BrynCooke](https://github.com/BrynCooke) in https://github.com/apollographql/router/pull/3703

apollo-router/src/uplink/mod.rs

@@ -4,6 +4,7 @@ use std::time::Duration;
 use std::time::Instant;
 
 use futures::Stream;
+use futures::StreamExt;
 use graphql_client::QueryBody;
 use thiserror::Error;
 use tokio::sync::mpsc::channel;
@@ -169,6 +170,17 @@ where
 {
     let query = query_name::<Query>();
     let (sender, receiver) = channel(2);
+    let client = match reqwest::Client::builder()
+        .timeout(uplink_config.timeout)
+        .build()
+    {
+        Ok(client) => client,
+        Err(err) => {
+            tracing::error!("unable to create client to query uplink: {err}", err = err);
+            return futures::stream::empty().boxed();
+        }
+    };
+
     let task = async move {
         let mut last_id = None;
         let mut endpoints = uplink_config.endpoints.unwrap_or_default();
@@ -181,13 +193,7 @@ where
 
             let query_body = Query::build_query(variables.into());
 
-            match fetch::<Query, Response>(
-                &query_body,
-                &mut endpoints.iter(),
-                uplink_config.timeout,
-            )
-            .await
-            {
+            match fetch::<Query, Response>(&client, &query_body, &mut endpoints.iter()).await {
                 Ok(response) => {
                     tracing::info!(
                         counter.apollo_router_uplink_fetch_count_total = 1,
@@ -255,13 +261,13 @@ where
     };
     drop(tokio::task::spawn(task.with_current_subscriber()));
 
-    ReceiverStream::new(receiver)
+    ReceiverStream::new(receiver).boxed()
 }
 
 pub(crate) async fn fetch<Query, Response>(
+    client: &reqwest::Client,
     request_body: &QueryBody<Query::Variables>,
     urls: &mut impl Iterator<Item = &Url>,
-    timeout: Duration,
 ) -> Result<UplinkResponse<Response>, Error>
 where
     Query: graphql_client::GraphQLQuery,
@@ -272,7 +278,7 @@ where
     let query = query_name::<Query>();
     for url in urls {
         let now = Instant::now();
-        match http_request::<Query>(url.as_str(), request_body, timeout).await {
+        match http_request::<Query>(client, url.as_str(), request_body).await {
             Ok(response) => {
                 let response = response.data.map(Into::into);
                 match &response {
@@ -352,14 +358,13 @@ fn query_name<Query>() -> &'static str {
 }
 
 async fn http_request<Query>(
+    client: &reqwest::Client,
     url: &str,
     request_body: &QueryBody<Query::Variables>,
-    timeout: Duration,
 ) -> Result<graphql_client::Response<Query::ResponseData>, reqwest::Error>
 where
     Query: graphql_client::GraphQLQuery,
 {
-    let client = reqwest::Client::builder().timeout(timeout).build()?;
     // It is possible that istio-proxy is re-configuring networking beneath us. If it is, we'll see an error something like this:
     // level: "ERROR"
     // message: "fetch failed from all endpoints"