Q: Persistent TimeoutError: ResourceRequest timed out (with 500 errors) on Vercel + MongoDB Atlas M0 using Waline v3

[tipsyoncola]

Describe the bug | 问题描述

Issue Body:

Environment:

• Deployment Platform: Vercel (Hobby Plan)
• Backend Package: @waline/vercel (set to latest in package.json, assumed to be v3 based on Vercel template/preview)
• Database: MongoDB Atlas (M0 Free Tier, AWS Asia Region)
• Vercel Function Region: Asia Region (same as database)
• Frontend: Hugo (Stack Theme) + Waline Client v3 (loaded @waline/client@v3 via unpkg in waline.html, displaying version v3.5.6)

Bug Description:

I deployed the backend using the latest Waline Vercel template and configured MongoDB Atlas M0 as the database. The frontend is also using Waline Client v3 (v3.5.6). However, I am unable to use the comment functionality due to persistent timeout errors during comment loading and submission.

Problem Progression:

1. Initial Problem: When first setting MONGO_URI and DB_TYPE: MongoDB environment variables, the Vercel runtime logs consistently showed Error: Not initialized errors referencing leancloud-storage paths (resulting in 500 server errors). It appeared the backend was ignoring the MongoDB settings.
2. After Setting Individual Variables: After removing MONGO_URI and setting individual MongoDB environment variables (MONGO_HOST, MONGO_DB, MONGO_USER, MONGO_PASSWORD, MONGO_AUTHSOURCE, MONGO_OPT_SSL) and redeploying, the LeanCloud-related errors disappeared. This suggested the backend was now recognizing the intention to use MongoDB.
3. Current Problem (TimeoutError): However, now when attempting to load or submit comments, TimeoutError: ResourceRequest timed out errors occur in the Vercel runtime logs. The browser console shows 500 Internal Server Error along with Failed to fetch errors for the corresponding requests.
   • Observation: When clicking the submit button for a comment, the timeout-related error message appears very quickly, after about 2 seconds (which feels much shorter than Vercel's default timeout limit).

Steps Taken:

• Attempted configuration using both the MONGO_URI method and the individual MongoDB environment variables method.
• Matched the Vercel Function Region with the MongoDB Atlas Region.
• Cleared Vercel build cache and redeployed multiple times.
• Ensured index.js (or index.cjs) code uses the default (module.exports = Waline();).
• Configured the frontend waline.html to use the Waline Client v3 loading method.
• The backend package.json uses "latest" for the @waline/vercel version (assumed v3).
• Resolved CORS issues by adding header configurations in vercel.json (no longer seeing CORS errors).

Expected Behavior:

The comment functionality should work without timeouts.

Actual Behavior:

Backend requests result in timeout errors (Vercel: TimeoutError, Browser: 500).

Relevant Logs (Vercel Runtime Log Type):

TimeoutError: ResourceRequest timed out
    at ResourceRequest._fireTimeout (...)
    at Timeout.bound (...)
    ...

Question:

Are there known performance issues or timeout problems when using the Waline v3 backend with MongoDB Atlas M0 free tier on the Vercel Hobby plan? Is this issue likely caused by the performance limitations of the M0 tier, or is it possible that the @waline/vercel package itself requires optimization or bug fixes related to MongoDB interaction in this environment?

Any advice or potential solutions would be greatly appreciated.

Website URL | 问题网站

https://tipsyoncola.gitlab.io/posts/my-first-post/

Where your waline deploy? | 服务部署在哪里？

Vercel (Default)

Where your comment data store? | 数据存储在哪里？

MongoDB

[lizheming]

How you config mongodb？The env settings format should be like following doc https://waline.js.org/en/guide/database.html#mongodb

[tipsyoncola]

I'm using this Environmental Variables.

[lizheming]

Try this configuration. Remember to redeploy the service after updating.

MONGO_HOST=["cluster0-shard-00.sylehp5.mongodb.net","cluster0-shard-01.sylehp5.mongodb.net","cluster0-shard-02.sylehp5.mongodb.net"]
MONGO_PORT=[27017,27017,27017,27017]
MONGO_DB=waline
MONGO_USER=vercel-admin-user
MONGO_REPLICASET=atlas-12cebf-shard-0
MONGO_AUTHSOURCE=admin
MONGO_OPT_SSL=true
MONGO_PASSWORD=xxxx

[tipsyoncola]

I have configured the Vercel environment variables precisely according to the your guidance for individual MongoDB settings.
I'm still encountering TimeoutError: ResourceRequest timed out errors (accompanied by 500 errors in the browser) when loading or submitting comments, making the feature unusable.

With only the recommended individual environment variables set, no activity (connection attempts) was registered on the MongoDB Atlas Metrics graphs.

For testing purposes, I previously created a separate mongodb-connection.js script that read these environment variables, constructed a standard connection string, and explicitly attempted connection, calling this script from index.cjs. Only then did connection attempts (spikes) appear on the Atlas Metrics graphs. (However, this approach eventually led to ENOTFOUND or other connection errors).

mongodb-connection.js

const { MongoClient } = require('mongodb');

let cachedClient = null;
let cachedDb = null;

async function connectToDatabase() {
  if (cachedClient && cachedDb) {
    return { client: cachedClient, db: cachedDb };
  }

  const hostJSON = process.env.MONGO_HOST;
  const portJSON = process.env.MONGO_PORT;
  const dbName = process.env.MONGO_DB || 'waline';
  const user = process.env.MONGO_USER;
  const password = process.env.MONGO_PASSWORD;
  const replicaSet = process.env.MONGO_REPLICASET;
  const authSource = process.env.MONGO_AUTHSOURCE || 'admin';
  const ssl = process.env.MONGO_OPT_SSL !== 'false';

  if (!hostJSON || !portJSON || !dbName || !user || !password || !replicaSet) {
      throw new Error('MongoDB connection failed: MONGO_HOST, MONGO_PORT, MONGO_DB, MONGO_USER, MONGO_PASSWORD, and MONGO_REPLICASET environment variables are required for standard connection string.');
  }

  try {
    let hosts = [];
    let ports = [];
    try {
      hosts = JSON.parse(hostJSON);
      ports = JSON.parse(portJSON);
      if (!Array.isArray(hosts) || !Array.isArray(ports) || hosts.length === 0 || hosts.length !== ports.length) {
        throw new Error('MONGO_HOST and MONGO_PORT must be valid JSON arrays of the same length.');
      }
    } catch (e) {
      throw new Error(`Failed to parse MONGO_HOST or MONGO_PORT JSON: ${e.message}`);
    }

    const hostPortString = hosts.map((h, i) => `${h}:${ports[i]}`).join(',');
    const uri = `mongodb://${encodeURIComponent(user)}:${encodeURIComponent(password)}@${hostPortString}/${dbName}?replicaSet=${replicaSet}&authSource=${authSource}${ssl ? '&ssl=true' : ''}&retryWrites=true&w=majority`;

    const client = new MongoClient(uri, {
      serverSelectionTimeoutMS: 30000,
      connectTimeoutMS: 30000,
      socketTimeoutMS: 60000
    });

    await client.connect();
    const db = client.db(dbName);

    cachedClient = client;
    cachedDb = db;

    console.log('MongoDB connection successful!');
    return { client, db };
  } catch (error) {
    console.error('MongoDB connection error:', error);
    cachedClient = null;
    cachedDb = null;
    throw error;
  }
}

module.exports = connectToDatabase;

index.cjs

const Application = require('@waline/vercel');
const connectToDatabase = require('./mongodb-connection');

module.exports = async (req, res) => {

  try {
    await connectToDatabase();

    const app = Application({
      db: async () => {
        const { db } = await connectToDatabase();
        return db;
      },
      cors: false,
      plugins: [],
      async postSave(comment) {},
    });

    return app(req, res);
  } catch (error) {
    console.error('Request handling error:', error);
    return res.status(500).json({});
  }
};

Is there a known issue with @waline/vercel properly initiating a connection using these individual MongoDB environment variables on Vercel? Is there a required configuration step I might be missing, or an alternative approach needed for this specific setup? Or is this persistent timeout likely still due to the performance limitations of the Atlas M0 tier, even if the connection initiation logic based on environment variables alone is potentially flawed?

I really like the Waline comment system and would love to add it to my blog. Any help would be greatly appreciated!

[tipsyoncola]

I changed it to a different comment system.