Load Balancing

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  1. Load Balancing for MediaWiki

This article details load balancing configurations for a MediaWiki 1.40 installation. Load balancing distributes network and application traffic across multiple servers, enhancing performance, reliability, and availability. It's a crucial component for any high-traffic MediaWiki site. This guide is intended for newcomers to server administration and assumes a basic understanding of web servers and databases.

What is Load Balancing?

Imagine a single doorway to a popular concert. Everyone has to go through that one door, causing a bottleneck. Load balancing is like adding multiple doorways, allowing more people to enter simultaneously. In the context of MediaWiki, multiple web servers deliver web pages to users, and a load balancer distributes the requests among them. If one server fails, the load balancer automatically redirects traffic to the remaining healthy servers, ensuring continuous service.

Why Use Load Balancing with MediaWiki?

Several benefits drive the need for load balancing in a MediaWiki environment:

  • Increased Availability: If one server goes down, the others continue to handle requests.
  • Improved Performance: Distributing the load reduces response times and improves the user experience.
  • Scalability: Easily add more servers to handle growing traffic without impacting existing users.
  • Reduced Downtime: Maintenance can be performed on servers one at a time without taking the entire site offline.

Common Load Balancing Techniques

Several methods are used for load balancing. These include:

  • Round Robin: Requests are distributed sequentially to each server.
  • Least Connections: Requests are sent to the server with the fewest active connections.
  • IP Hash: The client's IP address is used to determine which server receives the request. This ensures a user consistently connects to the same server (important for sessions).
  • URL Hash: The requested URL is used to determine the server.
  • Weighted Load Balancing: Servers are assigned weights based on their capacity.

Software and Hardware Options

Both software and hardware load balancers are available.

  • Hardware Load Balancers: Dedicated appliances offering high performance and reliability. Examples include F5 Networks BIG-IP and Citrix ADC. These are generally more expensive.
  • Software Load Balancers: Software running on standard servers. Common options include:
   * HAProxy: A popular, open-source load balancer.
   * Nginx: A versatile web server that can also function as a load balancer. See Nginx configuration for details.
   * Apache:  Can be configured for basic load balancing, but less common than HAProxy or Nginx. See Apache web server for details.
   * Keepalived: Primarily for virtual IP address management and failover, often used in conjunction with other load balancing solutions. See Keepalived setup.

Example Configuration: HAProxy

This section outlines a basic HAProxy configuration for load balancing two MediaWiki servers. Assume two servers: `mediawiki1.example.com` and `mediawiki2.example.com`.

Here’s a sample `haproxy.cfg` file:

``` frontend mediawiki_frontend 

   bind *:80
   mode http
   default_backend mediawiki_backend

backend mediawiki_backend 

   mode http
   balance roundrobin
   server mediawiki1.example.com:80 check
   server mediawiki2.example.com:80 check

```

This configuration listens on port 80 and distributes requests using the round-robin method to the two MediaWiki servers. The `check` option periodically verifies the health of each server. See HAProxy documentation for more advanced configuration options.

Server Specifications

The following table outlines recommended server specifications for MediaWiki load balancing:

Server Role CPU RAM Storage Operating System
Web Server (MediaWiki) 4+ Cores 8GB+ 100GB+ SSD Linux (Ubuntu, CentOS, Debian)
Load Balancer (HAProxy/Nginx) 2+ Cores 4GB+ 50GB+ SSD Linux (Ubuntu, CentOS, Debian)
Database Server 8+ Cores 16GB+ 500GB+ SSD Linux (Ubuntu, CentOS, Debian)

Database Considerations

Load balancing the web servers does *not* automatically load balance the database. The MediaWiki servers will all be connecting to the same database server. For high availability, consider:

  • Database Replication: Set up a read-only replica of your database. Web servers can read from the replica, reducing load on the primary database. See Database replication.
  • Database Clustering: More complex, but provides higher availability and scalability.
  • Solid State Drives (SSDs): Essential for database performance.

Session Management

Proper session management is critical when using load balancing. If a user is directed to one server, they need to remain on that server for the duration of their session. Several options exist:

  • Sticky Sessions (IP Hash): As mentioned earlier, uses the client's IP address to ensure consistent routing. However, this can be problematic with shared IP addresses (e.g., behind a proxy).
  • Session Storage in Database: Store session data in a shared database accessible by all web servers. This is the most reliable method. See Session management.
  • Shared Filesystem: Use a shared filesystem (e.g., NFS) to store session data. Less common due to potential performance and reliability issues.

Monitoring and Logging

Monitoring your load balancing setup is essential for identifying and resolving issues. Key metrics to monitor include:

  • Server Load: CPU usage, memory usage, disk I/O.
  • Request Rate: Requests per second.
  • Response Time: Average time to serve a request.
  • Error Rate: Number of errors.

Use tools like:

  • Nagios: A comprehensive monitoring system. See Nagios configuration.
  • Zabbix: Another popular monitoring solution.
  • Prometheus: A systems monitoring and alerting toolkit.
  • HAProxy Stats Page: Provides real-time statistics about your HAProxy configuration.

The following table summarizes common log files to monitor:

Log File Location Purpose
Access Log Web Server (e.g., /var/log/apache2/access.log) Records all incoming requests
Error Log Web Server (e.g., /var/log/apache2/error.log) Records errors and warnings
HAProxy Log /var/log/haproxy.log (or configured location) Records HAProxy statistics and errors

Troubleshooting

  • Server Down: Verify the server is running and accessible. Check the web server error logs.
  • Slow Response Times: Investigate server load, database performance, and network latency.
  • Session Issues: Ensure session management is configured correctly. Verify sticky sessions are working as expected or that shared session storage is accessible.
  • Load Imbalance: Check the load balancer configuration and ensure servers are properly weighted.

Further Resources


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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