Understanding the Topology Destroyed Error
When you encounter the MongoError: Topology was destroyed message in your Node.js application using Mongoose, it indicates that an operation was attempted on a MongoDB connection that was closed or no longer accessible. This could occur for several reasons, including idle timeouts, network issues, or explicit connection closures in your code that precede database operations.
Troubleshooting the Error
It’s essential to check for any intentional connection closures in your code – any call to mongoose.disconnect() or connection.close() that may occur before your operations complete. Adjusting these calls can prevent operations from being attempted on a closed connection.
If connections are being closed due to idle timeouts or transient network problems, consider implementing a robust connection and reconnection strategy. You can configure Mongoose to handle reconnections by setting the autoReconnect flag and specifying reconnectTries and reconnectInterval options.
Configuring Mongoose for Reconnection
Here’s an example configuring Mongoose to handle disconnections gracefully:
const mongoose = require('mongoose');
const options = {
autoReconnect: true,
reconnectTries: Number.MAX_VALUE,
reconnectInterval: 1000
};
async function connectWithRetry() {
try {
await mongoose.connect('mongodb://localhost:27017/yourdb', options);
console.log('MongoDB is connected');
} catch (err) {
console.log('MongoDB connection unsuccessful, retry after 5 seconds.');
setTimeout(connectWithRetry, 5000);
}
}
connectWithRetry();
By using an async function that employs a delay before retrying, you can attempt to establish a connection repeatedly when it fails. Additionally, by monitoring the connected, disconnected, and reconnectFailed events using listeners, you can create finer control and logging on your connection status:
mongoose.connection.on('connected', () => {
console.log('Mongoose connected to the database');
});
mongoose.connection.on('error', (err) => {
console.log(`Mongoose connection error: ${err}`);
});
mongoose.connection.on('disconnected', () => {
console.log('Mongoose disconnected');
});
process.on('SIGINT', async () => {
await mongoose.connection.close();
console.log('MongoDB connection closed due to app termination');
process.exit(0);
});
The proper management of events and connection life cycle goes a long way in mitigating the Topology was destroyed errors. However, if the issue persists it may be due to deeper networking issues or a bug within the version of the MongoDB driver you are using. Ensure you are running the latest version of the Mongoose and MongoDB driver compatible with your MongoDB server version.
