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Understanding Heartbeats in Distributed Systems - How Servers Detect Failures

What is a Heartbeat in Distributed Systems?

In distributed systems, data and tasks are spread across multiple servers to improve performance and reliability. But to manage these systems efficiently, each server must know which other servers are currently active and healthy.

That's where heartbeats come in.

Why Are Heartbeats Important?

When a request arrives at a server in a decentralized system, the server needs enough information to forward that request to the right server. This is only possible if each server knows the status of others in the network. Detecting server failures early ensures the system can quickly shift work to healthy servers, preventing further issues and maintaining overall system stability.

How Heartbeats Work

A heartbeat is a simple, periodic message that a server sends to show that it's still active. These messages can be sent to:

  • A central monitoring server, or
  • A random subset of peer servers in decentralized systems.

If a server fails to send its heartbeat within a specific timeout period, it's assumed to be offline or crashed. At that point, the system stops routing requests to the failed server and takes action to replace or redistribute its tasks.

Centralized vs. Decentralized Heartbeats

  • Centralized System: All servers report to a central monitor with regular heartbeat signals. If the monitor doesn't hear from a server in time, it flags it as failed.

  • Decentralized System: Each server randomly selects peers to send heartbeat messages. If multiple peers report a server is silent, the system marks it as potentially failed.

Conclusion

Heartbeat mechanisms are a critical part of failure detection in distributed systems. They allow the network to stay aware of which components are healthy and to reroute tasks when failures occur—ensuring high availability and resilience.