C++ Programming Practice: IP Hash Load Balancing Algorithm

Today we are going to learn about NGINX.

Nginx is a high-performance open source web server and reverse proxy server that can efficiently handle high concurrent requests.

The following are some of the main features and techniques of Nginx for handling high concurrency:

• Event-driven model: Nginx uses an event-driven asynchronous non-blocking processing method, using a single thread or a small number of threads to handle a large number of concurrent requests. It uses an event loop mechanism to listen to connections and requests from clients, and does not create a new thread or process for each request, reducing resource overhead.
• Multi-process/multi-thread: Nginx supports multi-process or multi-thread model, by duplicating the main process to create child processes or using thread pools to handle requests. This enables Nginx to take full advantage of multi-core processors and improve concurrent processing capabilities.
• Reverse proxy and load balancing: As a reverse proxy server, Nginx can forward requests to multiple backend servers to achieve load balancing. By configuring different load balancing algorithms (such as polling, IP hash, least connection, etc.), Nginx can distribute requests to different backend servers to disperse the load and improve the overall concurrent processing capability.
• Efficient event handling mechanism: Nginx uses efficient event handling mechanisms, such as epoll (Linux), kqueue (FreeBSD/MacOS) or select/poll (general), which can handle a large number of concurrent connections.
• Efficient memory management: Nginx uses its own memory pool management system to avoid frequent memory allocation and release operations, reduce memory fragmentation, and improve memory utilization.
• Static resource caching: Nginx supports caching of static resources. It can cache frequently accessed static files (such as images, CSS, JS, etc.) in memory, reduce requests to the backend server, and improve response speed and concurrent processing capabilities.
• Customizability and scalability: Nginx itself is highly customizable and scalable. Various parameters can be adjusted and optimized through configuration files to meet the needs of different scenarios. In addition, Nginx also supports the addition of third-party modules, which can add additional functions and features as needed.

Combining the above features and technologies, Nginx can effectively handle high-concurrency requests and provide stable and high-performance services. It is widely used in the Internet field, especially in large websites, application server clusters and CDN (content distribution network) scenarios, playing an important role.

IP hash is a load balancing algorithm that distributes requests to backend servers based on the client's IP address. Its basic principle is to calculate a hash value using a hash function based on the client's IP address, and then modulo the hash value with the length of the backend server list to determine which backend server the request should be sent to.

Here are the brief steps of IP hashing algorithm:

1. Get the client's IP address: When a request arrives, Nginx will get the client's IP address.
2. Calculate hash value: Use a hash function (such as MD5, SHA1, etc.) and take the client's IP address as input to calculate a hash value.
3. Modulo operation: Take the hash value modulo the length of the backend server list to get a remainder.
4. Determine the target server: Based on the remainder, determine which server in the backend server list the request should be sent to. Typically, the backend server list is an array or linked list in which each server has an index number.
5. Forward request: forward the request to the target server.

The advantage of the IP hash algorithm is that for the same IP address, requests initiated at any time and from any place will be distributed to the same backend server, which can maintain session continuity and stability to a certain extent. But at the same time, it may cause load imbalance problems, because some IP addresses may be concentrated on certain specific backend servers, causing some servers to be overloaded.

In Nginx, it is very simple to configure the load balancing strategy of IP hash algorithm. Just use the `ip_hash` directive in the configuration file to enable the IP hash algorithm. The following is an example configuration:

 http { upstream backend { ip_hash; server backend1.example.com; server backend2.example.com; server backend3.example.com; } server { listen 80; location / { proxy_pass http://backend; } } }

In the above example, the `ip_hash` directive is used to define the `backend` backend server group. Requests are hashed based on the client's IP address and dispatched to the corresponding backend server.

In summary, the IP hash algorithm is a commonly used load balancing algorithm in Nginx, which can distribute requests to backend servers according to the client's IP address to maintain the continuity and stability of the session.