Blast Radius

Blast radius means how much of a system is affected when something goes wrong.

Think of dropping a stone into water:

        💥
      (   )
    (       )
  (           )

The bigger the affected area, the bigger the blast radius.

Suppose your application has:

Auth
Users
Posts
Comments
Notifications

If a bug in the Posts module only breaks posts:

Posts 💥
Users       ✅
Comments    ✅
Notifications ✅

→ Small blast radius

But if everything depends directly on one shared module and a bug there breaks the entire application:

Auth          ❌
Users         ❌
Posts         ❌
Comments      ❌
Notifications ❌

→ Large blast radius

A good architecture tries to limit blast radius.

For example:

modular architecture → failures stay more isolated
feature flags → disable one feature without taking down everything
independent services → one service can fail while others continue
retries/timeouts → prevent one failing dependency from taking down the whole system

Simple definition:

Blast radius = the scope of damage caused by a failure or change.

You can also hear it in security: “If this account is compromised, what’s its blast radius?” — meaning what can the attacker affect?

reyhan base