feat(common): implement LRU connection cache and circuit breakers

packages/common/src/utils/connection.manager.js

@@ -1,13 +1,56 @@
-const { registry } = require("./registry");
+const { registry, circuitBreakers } = require("./registry");
 const { getPublicIp } = require("./network");
 const Project = require("../models/Project");
 const { decrypt } = require("./encryption");
 const mongoose = require("mongoose");
 const redis = require("../config/redis");
 
+const CB_MAX_FAILURES = 3;
+const CB_TIMEOUT_MS = 30000; // 30 seconds
+
+function recordFailure(key) {
+    const state = circuitBreakers.get(key) || { failures: 0, openUntil: null, probeInFlight: false };
+    state.failures += 1;
+    state.probeInFlight = false;
+    if (state.failures >= CB_MAX_FAILURES) {
+        console.warn(`[CIRCUIT BREAKER] Tripped OPEN for project ${key} due to ${state.failures} failures.`);
+        state.openUntil = Date.now() + CB_TIMEOUT_MS;
+    }
+    circuitBreakers.set(key, state);
+}
+
+function recordSuccess(key) {
+    if (circuitBreakers.has(key)) {
+        const state = circuitBreakers.get(key);
+        state.probeInFlight = false;
+        circuitBreakers.delete(key);
+    }
+}
+
 async function getConnection(projectId) {
     const key = projectId.toString();
 
+    // 0. Circuit Breaker Check (Fast Fail)
+    const cbState = circuitBreakers.get(key);
+    if (cbState) {
+        if (cbState.openUntil && Date.now() < cbState.openUntil) {
+            const error = new Error(`Service Unavailable: Database for project ${key} is currently unreachable. Circuit breaker is OPEN.`);
+            error.status = 503;
+            throw error;
+        } else if (cbState.openUntil && Date.now() >= cbState.openUntil) {
+            if (cbState.probeInFlight) {
+                // Reject concurrent callers while the single half-open probe is in flight
+                const error = new Error(`Service Unavailable: Database for project ${key} is currently unreachable. Circuit breaker is probing.`);
+                error.status = 503;
+                throw error;
+            }
+            // Half-open: Timeout expired, allow one retry probe
+            cbState.openUntil = null;
+            cbState.probeInFlight = true;
+            circuitBreakers.set(key, cbState);
+        }
+    }
+
     // 1. Instant Cache Hit (Fastest Path for UX)
     if (registry.has(key)) {
         const cachedConn = registry.get(key);
@@ -51,6 +94,7 @@ async function getConnection(projectId) {
             plan = projectDoc.plan || 'free';
         } catch (err) {
             console.error("Decryption Error:", err);
+            // Treat decryption errors as hard failures, don't trip breaker for user config errors, but we can't connect anyway
             throw new Error("Invalid or corrupted external config");
         }
 
@@ -83,8 +127,11 @@ async function getConnection(projectId) {
 
     try {
         await connection.asPromise();
+        recordSuccess(key); // Reset failures on successful connection
     } catch (err) {
         console.error("❌ Initial Connection Failed:", err.message);
+        recordFailure(key); // Increment circuit breaker failures
+
         if (err.message.includes("Server selection timed out") || err.message.includes("Could not connect")) {
             const serverIp = await getPublicIp();
             throw new Error(`Access Denied: Please whitelist Server IP [${serverIp}] in MongoDB Atlas.`);
@@ -94,20 +141,22 @@ async function getConnection(projectId) {
 
     connection.on("error", (err) => {
         console.error(`❌ DB Connection Error for project ${projectId}:`, err);
-        registry.delete(key); // Clear bad connections immediately
+        if (registry.deleteIfCurrent(key, connection)) {
+            recordFailure(key); // Only record failure if it was the active connection
+        }
     });
 
     connection.on("disconnected", () => {
         console.log(`🔌 External DB disconnected: ${projectId}`);
-        registry.delete(key);
+        registry.deleteIfCurrent(key, connection);
     });
 
     connection.on("close", () => {
-        registry.delete(key);
         console.log(`🔌 Connection closed: ${key}`);
+        registry.deleteIfCurrent(key, connection);
     });
 
-    // Save back to your central in-memory store
+    // Save back to your central in-memory store (LRU handles the capacity limit internally)
     registry.set(key, connection);
 
     return connection;

packages/common/src/utils/registry.js

@@ -1,3 +1,80 @@
-const registry = new Map();
-const storageRegistry = new Map();
-module.exports = { registry, storageRegistry };
+class LruConnectionMap {
+    constructor(maxSize, onEvict) {
+        this.map = new Map();
+        this.maxSize = maxSize;
+        this.onEvict = onEvict;
+    }
+
+    get(key) {
+        if (!this.map.has(key)) return undefined;
+        // Move to end to mark as recently used
+        const val = this.map.get(key);
+        this.map.delete(key);
+        this.map.set(key, val);
+        return val;
+    }
+
+    set(key, value) {
+        if (this.map.has(key)) {
+            this.map.delete(key);
+        } else if (this.map.size >= this.maxSize) {
+            // Evict oldest (least recently used)
+            const oldestKey = this.map.keys().next().value;
+            const oldestVal = this.map.get(oldestKey);
+            this.map.delete(oldestKey);
+            if (this.onEvict) {
+                try {
+                    this.onEvict(oldestKey, oldestVal);
+                } catch (e) {
+                    console.error(`Error during LRU eviction for ${oldestKey}:`, e);
+                }
+            }
+        }
+        this.map.set(key, value);
+    }
+
+    has(key) {
+        return this.map.has(key);
+    }
+
+    delete(key) {
+        return this.map.delete(key);
+    }
+
+    deleteIfCurrent(key, expectedValue) {
+        if (this.map.has(key) && this.map.get(key) === expectedValue) {
+            return this.map.delete(key);
+        }
+        return false;
+    }
+
+    get size() {
+        return this.map.size;
+    }
+
+    // Support Iterators for gc.js compatibility
+    *[Symbol.iterator]() {
+        yield* this.map[Symbol.iterator]();
+    }
+}
+
+// Mongoose connection pool registry (limit 50 to protect Node.js RAM/sockets)
+const registry = new LruConnectionMap(50, (key, conn) => {
+    console.log(`[LRU Eviction] Closing idle Mongoose connection for project ${key}`);
+    if (conn && typeof conn.close === 'function') {
+        conn.close().catch(err => console.error(`[LRU Eviction Error] Failed to close connection ${key}:`, err));
+    }
+});
+
+// Storage registry (S3/R2 clients, lower overhead so limit is higher)
+const storageRegistry = new LruConnectionMap(200, (key, client) => {
+    console.log(`[LRU Eviction] Removing idle storage client for project ${key}`);
+    if (client && typeof client.destroy === 'function') {
+        client.destroy();
+    }
+});
+
+// Circuit Breaker State Registry (Capped to prevent memory leak on inactive projects)
+const circuitBreakers = new LruConnectionMap(5000);
+
+module.exports = { registry, storageRegistry, circuitBreakers, LruConnectionMap };