How is load balancing achieved in Linux ? I need a conceptual understanding to implement solutions

Question

A simple scenario , I have implemented a Email server for my users to access / send emails . Now the users have grown and my server is not able to handle the load .

Now the question is why does a simple thing like email create a server load ?

Scenario 1) It has reached its network limits - bandwidth ( this can be fixed by askig ISP to give me more bandwidth so ruled out) or TCP/IP ports - max 64000 per server is only allowed if I am not mistaken . I reckon this possibility is more relevant . What would be a solution then ? Add more network cards and enable bonding ? If yes will the bonding take care of load balancing ? Again only 1 IP so how can this counter this problem ? Maybe Virtual IP's ?

Scenario 2) It is not able to process requests - (Processor not enough ). Now the solution is probably Clustering . How do I go about implementing this? Who takes care of load balance ? Would it be like 4 servers each having webserver package running with a IP ?

Answer 1

Considering your knowlege level you should find someone who knows what they're doing to evaluate your system and recommend upgrades or ways to improve efficiency.

Scenario 1a - Network bandwidth saturated. This is quite unlikely. You didn't mention anything about why you think there is a problem, but e-mail tends not to be bandwidth heavy unless you have a very large organization, and even then other factors of the system tend to be the bottleneck first.

Scenario 1b - Out of Ports. No, it doesn't work that way. Not even close.

Scenario 2 - Processor Capacity. This is more likely the issue, it also could be RAM, Disk Space, Disk Speed (throughput/latency), or something else entirely. Clustering is one potential option. A load balancing hardware device or specific software distributes connections; though you'll typically get more benefit from distributing the load intelligently by roll and/or destination.

Mail servers are not web servers, that's something else entirely. Computers must have IP addresses to work on the Internet; what kind of address will depend on your design.