Mongoose连接不同远程服务器双数据库时出现认证错误

Hey there, I've run into this exact issue before! The authentication error you're seeing when switching to remote IPs happens because you're reusing Mongoose's default singleton instance for both connections.

Local environments often let this slide (maybe your local MongoDB uses relaxed permissions, or both databases are on the same instance with shared credentials), but remote servers enforce strict authentication contexts. When you call mongoose.connect() twice, the second call overwrites the authentication details of the first, leading to that "not authorized" error when you try to query the first database.

The Fix: Use Separate Mongoose Instances #

You need to create independent Mongoose instances for each database connection. Each instance gets its own connection pool and authentication credentials, so they won't interfere with each other. Here's how to adjust your code:

const mongoose = require('mongoose');

// Create separate instances for each database
const db1Instance = mongoose.createConnection();
const db2Instance = mongoose.createConnection();

// Connect to first remote database
db1Instance.connect(`mongodb://${db.host}:${db.port}/${db.dbname}`, {
  user: db.username,
  pass: db.password,
  useUnifiedTopology: true,
  useNewUrlParser: true,
  useCreateIndex: true,
  useFindAndModify: false
})
.then(() => console.log(`db connection successful`))
.catch(err => logger.error("db connection1 error", err));

// Connect to second remote database
db2Instance.connect(`mongodb://${db2.host}:${db2.port}/${db2.dbname}`, {
  user: db2.username,
  pass: db2.password,
  useUnifiedTopology: true,
  useNewUrlParser: true,
  useCreateIndex: true,
  useFindAndModify: false
})
.then(() => console.log(`db connection2 successful`))
.catch(err => logger.error("db connection2 error", err));

Bonus: Using useDb for Same Cluster Databases #

If both databases are on the same remote MongoDB cluster and share the same authentication credentials, you can use useDb() on an existing connection instead of creating a new instance. This is more efficient since it reuses the connection pool:

const mongoose = require('mongoose');

// Connect to the main database first
mongoose.connect(`mongodb://${db.host}:${db.port}/${db.dbname}`, {
  user: db.username,
  pass: db.password,
  useUnifiedTopology: true,
  useNewUrlParser: true,
  useCreateIndex: true,
  useFindAndModify: false
})
.then(mainConn => {
  console.log(`main db connection successful`);
  // Access the second database using the same connection
  const db2 = mainConn.useDb(db2.dbname);
  // Now you can define schemas/models using db2 instead of the default mongoose instance
})
.catch(err => logger.error("main db connection error", err));

Quick Checks to Rule Out Other Issues #

• Double-check that your remote MongoDB firewall allows incoming connections from your main server's IP address.
• Verify that each remote database user has explicit permissions (like readWrite) for their respective database. The error message's "not authorized" could also mean missing permissions, but your local success makes connection confusion the likelier culprit.

内容的提问来源于stack exchange，提问作者Akshay seth