When it comes to building modern, high-performance systems, concurrency and fault tolerance are key considerations. Concurrency allows for multiple tasks to be executed in parallel, while fault tolerance ensures that a system can continue to operate even in the face of failures. While there are many programming languages and frameworks that can be used for this purpose, Elixir is an excellent choice for several reasons.

The Elixir’s built-in support for the Actor model of concurrency makes it an ideal choice for building concurrent systems. The Actor model is a mathematical model of concurrent computation that describes how a set of independent, concurrent processes interact with each other through message passing. In the Actor model, each process runs in its isolated environment, so it can’t access the state of other processes and can only communicate with other processes by sending and receiving messages. It gives us the ability to handle failures gracefully, so if one process crashes, it does not affect the other processes. This ensures that the state of the system is consistent, and it makes it much easier to reason about the system

The Actor model provides isolation between processes, so if one process crashes, it can be restarted without affecting the other processes. The Elixir’s supervision tree allows for monitoring the state of the processes and taking action if necessary.

The Elixir’s built-in support for the OTP (Open Telecom Platform) framework, provides a set of abstractions and tools for creating, managing, and monitoring processes, as well as libraries and patterns, it makes easy to troubleshoot and maintain the system, such as the IEx interactive shell and the Observer tool, which allows you to inspect the state of the processes and the supervision tree.

Additionally, Elixir runs on the Erlang’s VM (BEAM), which is designed to be distributed, so it can run multiple nodes on different machines and provide a garbage collector that is designed to work well in concurrent systems, and it also provides a scheduler that allows to scheduling processes efficiently and avoids contention.

The functional programming paradigm allows a more declarative and expressive style of coding, making it easier to reason about the system, and maintain it. Also, the Elixir community is growing fast, and there are many resources and libraries available.

So, Elixir’s built-in support for concurrency and fault tolerance makes it an excellent choice for building systems that need to handle high levels of traffic and scale horizontally.