Q: Developers experience 15-second page loads and HTTP 504 Gateway Timeouts on Backstage. Node.js backend CPU is pinned at 100%, and health checks fail. Profiling indicates a custom internal plugin is blocking the single-threaded event loop. How do you triage and optimize Backstage performance?

Install `@clinic/doctor` or enable Node.js `--prof` profiling. Inspect event loop delay metrics exposed via Prometheus by `@backstage/backend-common`.

# Prometheus metric showing event loop lag spike:
nodejs_eventloop_lag_seconds{job="backstage-backend"} > 5.0

Identify synchronous loops in custom plugins (e.g. `catalog.getEntities()` with nested synchronous regex evaluations). Refactor to stream entities in batches of 100 using asynchronous generators and `setImmediate()` yields, or offload heavy processing to Worker Threads.

// Offload blocking CPU loop using asynchronous batching
async function* processEntities(entities) {
  for (const chunk of chunkArray(entities, 100)) {
    yield processBatch(chunk);
    await new Promise(resolve => setImmediate(resolve)); // Yield to event loop
  }
}

Deploy Backstage with multiple cluster worker processes per container (`NODE_CLUSTER_WORKERS=4`) and cache expensive API responses in Redis with a 5-minute TTL.