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What is Circuit breakers?

Anubhav Sharma 977 05 Feb 2026

What is Circuit breakers, Explain with example?

1 Answers

ICSM Computer 09 Feb 2026

Circuit breakers are a resilience pattern used in software systems to prevent repeated failures from cascading and taking down your whole app.

Think of it like the electrical circuit breaker in your house.

The simple idea

If a remote service (API, database, SMTP server, payment gateway, etc.) keeps failing:

Don’t keep hammering it
Don’t block threads waiting forever
Don’t spread the failure to other parts of your system

Instead:

Trip the circuit
Fail fast
Recover gracefully

That’s a circuit breaker.

Why circuit breakers exist

Without a circuit breaker:

Your app calls a failing service
Requests time out
Threads pile up
CPU/memory spike
Your entire system slows down or crashes

With a circuit breaker:

Detect repeated failures
Stop calling the broken service temporarily
Return a fallback response immediately
Periodically test if the service is healthy again

Circuit breaker states

A circuit breaker has three states:

Closed (normal state)

Requests flow normally
Failures are counted
If failures cross a threshold → Open

Open (tripped)

Calls are blocked
Requests fail immediately
No waiting, no retries
After a cooldown period → Half-Open

Half-Open (testing mode)

Allows a few trial requests
If they succeed → Closed
If they fail → Open again

Real-world example

Imagine your Newsletter Worker Service sending emails:

SMTP server goes down
Every retry takes 30 seconds
1000 queued emails = disaster

With a circuit breaker:

After, say, 5 failures → circuit opens
Emails fail fast
Worker stays healthy
After 1 minute → test SMTP again

Circuit breaker vs Retry

These two work together, not against each other:

Pattern	Purpose
Retry	Handle temporary glitches
Circuit Breaker	Handle persistent failures

Best practice:

Retry inside
Circuit breaker outside

Circuit breakers in .NET (Polly)

In .NET, circuit breakers are usually implemented using Polly.

Conceptually:

Policy
    .Handle<Exception>()
    .CircuitBreaker(
        exceptionsAllowedBeforeBreaking: 5,
        durationOfBreak: TimeSpan.FromSeconds(60)
    );

This means:

5 failures → circuit opens
Stays open for 60 seconds
Then tries again

When should you use circuit breakers?

Use them when calling:

External APIs
Email/SMS gateways
Payment services
Databases over the network
Microservice-to-microservice calls

Avoid them for:

In-memory operations
Pure CPU logic
Deterministic code

Key takeaway

A circuit breaker protects your system from repeatedly calling something that is already broken, allowing it to recover instead of collapse.

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