What are the main aspects to consider when designing a system to ensure horizontal scalability of the application?

When designing a system for horizontal scalability, it is important to consider:

• Stateless architecture — so that new application instances can be processed without dependency on state.
• Load balancing — distributing requests among multiple servers.
• Data partitioning — sharding or replication of databases to distribute load.
• Caching — using external caches (e.g., Redis, Memcached) to reduce database load.
• Asynchronous processing — message queues and background tasks to offload main threads.
• Monitoring and auto-scaling — so the system can adapt to load.

These aspects help ensure that when new servers are added, the system operates correctly and efficiently.