1. Introduction

In today's world, creating a complex website or web application without using VPS (Virtual Private Server) is almost impossible. With the help of VPS, you can configure your virtual server according to your needs and requirements, install required software, create and manage databases, and much more. However, sometimes it's not enough to have only one VPS, and you may need to have several servers working together, in a synchronized and harmonized way. In this article, we'll describe how to sync multiple VPS and make them work as a cohesive unit.

2. Why do you need to sync multiple VPS?

There are several significant reasons why you may want to sync multiple VPS:

• The workload of your website or web application is too high, and you need to distribute it among your servers;
• You want to create high availability and redundancy for your system, so if one of the servers fails, the others can pick up the workload immediately;
• You're running a globally distributed system and need to ensure all nodes are coordinated and synchronized;
• You need to centralize your data in one place and ensure that all your servers can access it;
• You want to create a load-balanced system, where incoming requests are distributed among your servers.

3. Synchronization techniques

There are several techniques to sync multiple VPS, each with its own pros and cons. Here are the most commonly used methods:

• Unison: It's a file synchronization tool that allows you to sync files between different VPS. It works bi-directionally, so changes made on one server will be replicated to the others;
• rsync: It's similar to Unison, but it's one-directional. You can use it to copy files from one server to another, but changes made on the destination server won't be propagated back to the source server;
• NFS (Network File System): It's a file-sharing protocol that allows you to mount a remote file system on your local server. NFS is optimized for large files and high-speed networks;
• DRBD (Distributed Replicated Block Device): It's a method to synchronize block devices (hard disks, partitions) between different VPS. DRBD is synchronous, which means that changes are propagated immediately, ensuring that all servers have the same data at all times;
• GlusterFS: It's a distributed file system that allows you to create a synced and replicated storage pool across multiple VPS. GlusterFS is fault-tolerant and can survive the failure of several nodes;
• ZFS (Zettabyte File System): It's a file system that provides data storage features such as RAID, snapshots, and replication. ZFS is optimized for high capacity, high-speed networks, and very high reliability.

4. Load balancing and failover

Syncing multiple VPS is not only about replicating data, but it's also about ensuring that the workload is distributed evenly among your servers and that in case one of the servers fails, the others can take its place immediately. There are several load-balancing and failover techniques you can use, depending on your requirements:

• DNS Round Robin: It's the simplest load-balancing method, where you specify multiple IP addresses in your DNS record, and incoming requests are distributed among them in a round-robin fashion;
• HAProxy: It's a fast and lightweight load balancer that can distribute incoming requests among your servers based on various algorithms, such as round-robin, least connections, IP hash, and others;
• NGINX: It's a versatile web server that can function as a load balancer, reverse proxy, or web server. NGINX is fast, can handle a large number of concurrent requests, and can distribute them among your servers based on various criteria;
• Keepalived: It's a high-availability software that can create a virtual IP address shared by multiple servers, ensuring that if one fails, the others can take its place immediately.

5. Conclusion

Syncing multiple VPS can be a complex task, but with the right tools and techniques, you can create a scalable, fault-tolerant, and high-performance system. The key is to understand your requirements and choose the appropriate synchronization, load-balancing, and failover methods. Always test your system thoroughly before deploying it to your production environment and monitor it regularly to ensure it's running smoothly.