I'm currently working on nodejs application and I got small issue.
My NodeJS application consists of 2 parts:
We're receiving a lot of calls to API from our other internal applications. Some of this calls would generate notifications to web users (let's imaging it's online-chat). So if we have message for client #1000 and he's online (connected to Web application through Socket.io) we would emit message throught Socket.io to this client. Everything works fine.
But there is an issue.
We're going to introduce load balancer between our NodeJS application (it's one application, so both parts - API and Web would be behind the load balancer). Now let's imagine that we have load balancer and 2 servers with this application: server1 and server2. Thus some of API calls are sent to server1 and some of them are sent to server2. So let's imagine we got API call to server1 and this call should send a message to client #1000. But this client has open connection to server2.
The question is: is there any best practices or common solutions - how these two servers should communicate? One of possible solutions could be open socket connection between all servers with nodejs application and if we need to send a message to client - just broadcast it so every server could check if client is connected at this moment and send the message to correct client.