Load balancer

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  1. Load Balancer

A load balancer is a crucial component of a high-availability, scalable MediaWiki deployment. This article provides a technical overview of load balancers, their configuration considerations, and common choices for a MediaWiki environment. It is aimed at system administrators and engineers responsible for maintaining a MediaWiki installation.

What is a Load Balancer?

A load balancer distributes network traffic across multiple servers. In the context of MediaWiki, this means distributing user requests to several web servers hosting the wiki, database servers, or even caching servers. This offers several key benefits:

  • **Increased Availability:** If one server fails, the load balancer redirects traffic to the remaining healthy servers, minimizing downtime.
  • **Improved Scalability:** As traffic increases, you can add more servers to the pool, and the load balancer will automatically distribute the load.
  • **Enhanced Performance:** By distributing the load, individual servers aren't overwhelmed, leading to faster response times.
  • **Session Persistence (Sticky Sessions):** Some load balancers can ensure that a user's requests are consistently directed to the same server, which is important for maintaining session data, especially when PHP sessions are used.

Types of Load Balancers

There are two primary types of load balancers:

  • **Hardware Load Balancers:** These are dedicated physical appliances designed for high performance and reliability. They are generally more expensive but offer advanced features and dedicated support. Examples include F5 Networks BIG-IP and Citrix ADC.
  • **Software Load Balancers:** These run as software on standard servers. They are more flexible and cost-effective, but may require more configuration and management. Popular choices include HAProxy, Nginx, and Apache with `mod_proxy_balancer`.

Load Balancer Configuration Considerations

Configuring a load balancer for MediaWiki requires careful planning. Here are some key considerations:

  • **Health Checks:** Configure health checks to regularly monitor the status of each server in the pool. The load balancer should automatically remove unhealthy servers from the rotation. A simple HTTP health check pointing to a dedicated Maintenance page can be effective.
  • **Load Balancing Algorithms:** Choose an appropriate load balancing algorithm. Common options include:
   *   **Round Robin:** Distributes requests sequentially to each server.
   *   **Least Connections:** Sends requests to the server with the fewest active connections.
   *   **IP Hash:**  Uses the client's IP address to consistently route requests to the same server.
  • **Session Persistence:** Decide whether session persistence is required. If so, configure the load balancer to use cookies or other mechanisms to maintain session affinity. Consider the implications for scaling if sticky sessions are used.
  • **SSL Termination:** The load balancer can handle SSL/TLS encryption and decryption (SSL termination), reducing the load on the web servers. This is highly recommended for security.
  • **Caching:** Some load balancers offer caching capabilities, which can further improve performance. Consider integrating with a dedicated Caching system like Varnish or Memcached.
  • **Logging & Monitoring:** Enable detailed logging and monitoring to track load balancer performance and identify potential issues.


Example Configuration: HAProxy

HAProxy is a popular, open-source software load balancer. Here's a simplified example configuration for a MediaWiki setup:

Configuration Parameter Value
Frontend (Listening Port) 80, 443
Backend (Web Server Pool) wiki_backend
Web Server Addresses 192.168.1.10:80, 192.168.1.11:80, 192.168.1.12:80
Health Check Path /mw/index.php?title=Special:Maintenance
Load Balancing Algorithm roundrobin

This configuration listens on ports 80 and 443, distributes traffic to the web servers listed in the `wiki_backend` section, and performs health checks on the `/mw/index.php?title=Special:Maintenance` page. More complex configurations are possible for SSL termination and session persistence. Refer to the HAProxy documentation for detailed information.

Example Configuration: Nginx

Nginx can also function effectively as a load balancer. A basic configuration would resemble the following:

Configuration Parameter Value
Upstream Block ```nginx upstream wiki_backend { server 192.168.1.10:80; server 192.168.1.11:80; server 192.168.1.12:80; } ```
Server Block ```nginx server { listen 80; server_name wiki.example.com; location / { proxy_pass http://wiki_backend; } } ```
Health Checks Requires Nginx Plus or third-party modules

This configuration defines an upstream block containing the addresses of the web servers and then uses `proxy_pass` to forward requests to the upstream block. Health checks are more complex to implement with standard Nginx and often require the paid Nginx Plus version or third-party modules. See the Nginx documentation for more details.

Database Load Balancing

While less common, you can also load balance database connections. This is typically achieved using technologies like MariaDB Galera Cluster or PostgreSQL replication combined with a proxy like ProxySQL. Database load balancing is more complex than web server load balancing and requires careful consideration of data consistency and replication. A table summarizing database load balancing considerations:

Consideration Details
Replication Type Asynchronous vs. Synchronous. Synchronous replication provides stronger consistency but can impact performance.
Connection Pooling Essential for reducing database connection overhead. ProxySQL is well-suited for this.
Read/Write Splitting Route read queries to replica servers and write queries to the master server.
Failover Mechanism Ensure automatic failover to a replica server in case of master server failure.

Monitoring and Troubleshooting

Regular monitoring of the load balancer is essential. Key metrics to track include:

  • **Request Rate:** The number of requests per second.
  • **Response Time:** The average time it takes to process a request.
  • **Server Health:** The status of each server in the pool.
  • **Connection Count:** The number of active connections to each server.

Tools like Prometheus and Grafana can be used to visualize these metrics and set up alerts. Troubleshooting load balancer issues often involves examining logs, checking server health, and verifying the configuration.


Special:Mypreferences can also be helpful when debugging session related issues. Ensure proper Firewall configuration allows communication between the load balancer and the servers. Remember to regularly update your load balancer software to benefit from security patches and bug fixes.


Intel-Based Server Configurations

Configuration Specifications Benchmark
Core i7-6700K/7700 Server 64 GB DDR4, NVMe SSD 2 x 512 GB CPU Benchmark: 8046
Core i7-8700 Server 64 GB DDR4, NVMe SSD 2x1 TB CPU Benchmark: 13124
Core i9-9900K Server 128 GB DDR4, NVMe SSD 2 x 1 TB CPU Benchmark: 49969
Core i9-13900 Server (64GB) 64 GB RAM, 2x2 TB NVMe SSD
Core i9-13900 Server (128GB) 128 GB RAM, 2x2 TB NVMe SSD
Core i5-13500 Server (64GB) 64 GB RAM, 2x500 GB NVMe SSD
Core i5-13500 Server (128GB) 128 GB RAM, 2x500 GB NVMe SSD
Core i5-13500 Workstation 64 GB DDR5 RAM, 2 NVMe SSD, NVIDIA RTX 4000

AMD-Based Server Configurations

Configuration Specifications Benchmark
Ryzen 5 3600 Server 64 GB RAM, 2x480 GB NVMe CPU Benchmark: 17849
Ryzen 7 7700 Server 64 GB DDR5 RAM, 2x1 TB NVMe CPU Benchmark: 35224
Ryzen 9 5950X Server 128 GB RAM, 2x4 TB NVMe CPU Benchmark: 46045
Ryzen 9 7950X Server 128 GB DDR5 ECC, 2x2 TB NVMe CPU Benchmark: 63561
EPYC 7502P Server (128GB/1TB) 128 GB RAM, 1 TB NVMe CPU Benchmark: 48021
EPYC 7502P Server (128GB/2TB) 128 GB RAM, 2 TB NVMe CPU Benchmark: 48021
EPYC 7502P Server (128GB/4TB) 128 GB RAM, 2x2 TB NVMe CPU Benchmark: 48021
EPYC 7502P Server (256GB/1TB) 256 GB RAM, 1 TB NVMe CPU Benchmark: 48021
EPYC 7502P Server (256GB/4TB) 256 GB RAM, 2x2 TB NVMe CPU Benchmark: 48021
EPYC 9454P Server 256 GB RAM, 2x2 TB NVMe

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⚠️ *Note: All benchmark scores are approximate and may vary based on configuration. Server availability subject to stock.* ⚠️

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