server.ts

[...]
httpServer.listen({ port: config.port }, () => {
  console.log(`🚀 Server ready at http://localhost:${config.port}${server.graphqlPath}`)
  console.log(`🚀 Subscriptions ready at ws://localhost:${config.port}${server.subscriptionsPath}`)

  const connectMongoWithRetry = () => {
    mongoose
      .connect(config.mongoURI, {
        useNewUrlParser: true,
        useCreateIndex: true,
        useUnifiedTopology: true,
      })
      .then(() => console.log(`🚀 MongoDB connection ready at ${config.mongoURI}`))
      .catch(err => {
        console.error('MongoDB connection error', err);
        setTimeout(connectMongoWithRetry, 5000);
      });
  };

  connectMongoWithRetry();
});