proxy: add connect compute concurrency lock (#7607)

## Problem

Too many connect_compute attempts can overwhelm postgres, getting the
connections stuck.

## Summary of changes

Limit number of connection attempts that can happen at a given time.

proxy/src/console/provider.rs

@@ -17,7 +17,7 @@ use crate::{
     scram, EndpointCacheKey,
 };
 use dashmap::DashMap;
-use std::{sync::Arc, time::Duration};
+use std::{hash::Hash, sync::Arc, time::Duration};
 use tokio::sync::{OwnedSemaphorePermit, Semaphore};
 use tokio::time::Instant;
 use tracing::info;
@@ -447,16 +447,16 @@ impl ApiCaches {
 }
 
 /// Various caches for [`console`](super).
-pub struct ApiLocks {
+pub struct ApiLocks<K> {
     name: &'static str,
-    node_locks: DashMap<EndpointCacheKey, Arc<Semaphore>>,
+    node_locks: DashMap<K, Arc<Semaphore>>,
     permits: usize,
     timeout: Duration,
     epoch: std::time::Duration,
     metrics: &'static ApiLockMetrics,
 }
 
-impl ApiLocks {
+impl<K: Hash + Eq + Clone> ApiLocks<K> {
     pub fn new(
         name: &'static str,
         permits: usize,
@@ -475,10 +475,7 @@ impl ApiLocks {
         })
     }
 
-    pub async fn get_wake_compute_permit(
-        &self,
-        key: &EndpointCacheKey,
-    ) -> Result<WakeComputePermit, errors::WakeComputeError> {
+    pub async fn get_permit(&self, key: &K) -> Result<WakeComputePermit, errors::WakeComputeError> {
         if self.permits == 0 {
             return Ok(WakeComputePermit { permit: None });
         }

proxy/src/console/provider/neon.rs

@@ -13,7 +13,7 @@ use crate::{
     http,
     metrics::{CacheOutcome, Metrics},
     rate_limiter::EndpointRateLimiter,
-    scram, Normalize,
+    scram, EndpointCacheKey, Normalize,
 };
 use crate::{cache::Cached, context::RequestMonitoring};
 use futures::TryFutureExt;
@@ -25,7 +25,7 @@ use tracing::{error, info, info_span, warn, Instrument};
 pub struct Api {
     endpoint: http::Endpoint,
     pub caches: &'static ApiCaches,
-    pub locks: &'static ApiLocks,
+    pub locks: &'static ApiLocks<EndpointCacheKey>,
     pub endpoint_rate_limiter: Arc<EndpointRateLimiter>,
     jwt: String,
 }
@@ -35,7 +35,7 @@ impl Api {
     pub fn new(
         endpoint: http::Endpoint,
         caches: &'static ApiCaches,
-        locks: &'static ApiLocks,
+        locks: &'static ApiLocks<EndpointCacheKey>,
         endpoint_rate_limiter: Arc<EndpointRateLimiter>,
     ) -> Self {
         let jwt: String = match std::env::var("NEON_PROXY_TO_CONTROLPLANE_TOKEN") {
@@ -289,7 +289,7 @@ impl super::Api for Api {
             return Err(WakeComputeError::TooManyConnections);
         }
 
-        let permit = self.locks.get_wake_compute_permit(&key).await?;
+        let permit = self.locks.get_permit(&key).await?;
 
         // after getting back a permit - it's possible the cache was filled
         // double check