Build a Backend-for-Frontend (BFF)

Fan-out/fan-inGraceful degradationRequest tracing

Your frontend needs a single API call to render a dashboard, but the data lives across three independent backend services:

- User Service — returns the current user's profile and preferences

- Catalog Service — returns available items with metadata (title, description, category)

- Activity Service — returns the user's recent activity and notifications

Your job is to build a BFF (Backend-for-Frontend) that:

1. Receives a single GET /v1/pages/home?user_id=abc request from the client

2. Calls all three downstream services in parallel

3. Assembles everything into a single JSON response with a section per service

4. If a downstream call fails or times out, that section returns an error field instead of failing the entire response

5. Total response time must be under 500ms even if one service is slow

The downstream service URLs are provided via environment variables (USER_SERVICE_URL, CATALOG_SERVICE_URL, ACTIVITY_SERVICE_URL).

Constraints

●All downstream calls must be concurrent (goroutines / threads / async)

●Per-service timeout: 300ms

●Overall request timeout: 500ms

●A failed or slow service must not break the entire response — degrade gracefully

●Must propagate X-Request-Id header to all downstream calls (generate one if missing)

Hints

Test Cases (6)

1. All services healthy

Response contains all three sections with data

2. One service returns 500

That section has error field, others are fine

3. One service takes 2 seconds

That section times out, others return normally

4. All services healthy — check latency

Total response time < 500ms (parallel, not sequential)

5. Missing X-Request-Id

BFF generates one and propagates it to all downstream calls

6. A service returns empty data

Section has empty items: [], not an error

Solution

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Test Results

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