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Medium · Grade 216. Real-Time Provider Health

Route to Provider A while online, then fallback to Provider B when Provider A drops.

Scenario

Provider A starts online, but drops mid-run. Provider B remains online continuously.

Problem statement

Static routing breaks when provider health changes mid-run!

In this challenge, Provider A starts online and offers optimal rates, but drops offline halfway through processing the queue. Provider B remains online throughout.

Set up dynamic routing: send transactions to Provider A while onlineA is true, and fall back to Provider B (onlineB) when Provider A drops.

Order rules dynamically: 1. WHEN onlineA -> DO route-a 2. WHEN onlineB -> DO route-b

While A is online, rule 1 fires. When A goes offline mid-run, rule 1 fails to match and rule 2 seamlessly takes over.

What this teaches

Build dynamic fallbacks that adapt to live environmental state changes and provider outages.

Scroll down to build and test your solution.

Active controller

Apply & Run executes only the selected controller.

How a rule works

A rule has two parts:

WHEN <something is true> → DO <this action>

  • WHEN is a question about what is happening right now. For example: "Is it raining?" or "Is there a wall ahead?"
  • DO is what happens when the answer is yes.
  • The simulation runs one step at a time.
  • On each step, the rules are checked from top to bottom.
  • The first rule that is true wins. The rules below it are skipped for that step.
  • To change which rule wins, move it up or down the list.
  • If no rule is true, nothing happens on that step.
  • Some actions have more than one step, like "turn right, then move". You build these in the Functions tab.
  • Once a multi-step action starts, it finishes all its steps before the rules are checked again. It only stops early if the next step is not safe.
See an example

Two rules for deciding about an umbrella:

1  WHEN isRaining  → take an umbrella
2  WHEN always     → leave the umbrella at home
  • It is raining. Rule 1 is true, so you take an umbrella. Rule 2 is skipped.
  • It is sunny. Rule 1 is false, so rule 2 is checked next. Rule 2 is always true, so you leave the umbrella at home.
  • Order matters. If rule 2 were on top, it would be true every day, and you would never take an umbrella.

Rule folders

Categorise cards without changing their global execution order.

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Folder
WHEN
DO