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System Design

The Routing Slip

A message carries its own ordered list of processing steps.

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What it is

A routing slip attaches a list of processing steps to a message so it visits each step in order. Like a paper slip stapled to a folder, it tells each station where the message goes next.

How it works

  • A component computes the sequence of steps the message needs.
  • The slip is attached to the message.
  • Each step processes the message, then forwards it to the next step named on the slip.

Why it matters

  • Builds a dynamic pipeline without a central coordinator.
  • Different messages can follow different routes based on their needs.
  • Each step stays simple: do work, advance the slip.

A routing slip suits workflows where the path is known up front but varies per message, such as conditional approval chains. It is decentralized: the message carries its itinerary, so there is no orchestrator to bottleneck. The limit is that the slip is fixed when computed; for branching that depends on intermediate results, a process manager is the better fit.

Key idea

A routing slip travels with the message as an ordered itinerary, letting each step forward it to the next without a central coordinator.

Check yourself

Answer to earn rating on the learn ladder.

1. Where is the sequence of steps stored in a routing slip?

2. When is a process manager preferred over a routing slip?