Load Balancing Stateless vs Stateful
Load Balancing Stateless
Stateless Load Balancing is an approach in which the Load Balancer does not store information about the user’s session state. Each incoming request is treated independently, regardless of previous requests from the same user. Some of the advantages and disadvantages of Load Balancing Stateless are:
Advantages:
- Simplicity: Implementation is simpler because there is no need to track session status.
- Scalability: It is easier to scale because each request is treated independently.
- Failure Tolerance: If a Load Balancer fails, requests can be easily routed to another Load Balancer without affecting the user’s session.
Disadvantages:
- Session Consistency: Difficulty in maintaining user session consistency, which is important for applications that require continuous session data.
- Session Management: Requires additional techniques to manage user sessions, such as storing sessions on a server or using cookies.
Load Balancing Stateful
Load Balancing Stateful is an approach in which a Load Balancer stores information about the user’s session state. Any requests from the same user are directed to the same server to maintain session consistency. Some of the advantages and disadvantages of Load Balancing Stateful are:
Advantages:
- Session Consistency: Ensures requests from the same user are always directed to the same server, maintaining consistent session data.
- User Experience: Improve the user experience by maintaining continuous and consistent sessions.
Disadvantages:
- Complexity: Implementations are more complex because they require tracking and storing session state.
- Limited Scalability: Harder to scale due to the dependency on the session state.
- Failure Tolerance: If the Load Balancer or the server that stores the session state fails, the user’s session can be interrupted or lost.
Load Balancing Techniques
In this section, we will discuss some commonly used load balancing techniques, along with how they work, advantages, disadvantages, and examples of their application.
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1. Round Robin
Round robin is the simplest load-balancing technique. This technique distributes requests in turn to all available servers, without considering other factors such as the current server workload or server response time.
How it works:
- The load balancer receives a request from the client.
- The load balancer selects the next server in the list in order.
- The load balancer sends a request to the selected server.
- The server processes the request and sends the response to the client.
Excess:
- Simple and easy to implement.
- Fair for all servers.
Deficiency:
- It does not consider the current server workload or server response time.
- A weaker server can be overloaded if there are other, stronger servers.
Application Example:
- Websites with static and predictable traffic.
- Simple web application with a balanced workload between servers.
2. Least Connections
Least connections is a load balancing technique that selects the server with the lowest number of connections to handle new requests. This technique aims to distribute the workload evenly and avoid overloading a particular server.
How it works:
- The load balancer receives a request from the client.
- The load balancer selects the server with the lowest number of connections.
- The load balancer sends a request to the selected server.
- The server processes the request and sends the response to the client.
Excess:
- Distribute workloads evenly between servers.
- Avoid overloading certain servers.
Deficiency:
- A server that has just completed a lot of requests may still have fewer resources than other servers, even though it has fewer connections.
- Does not consider server response time.
Application Example:
- Web applications with dynamic and unpredictable workloads.
- Applications that are sensitive to response times, such as VoIP applications or online games.