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Pascual Vila

Frontend Instructor // Code Syllabus

Common Pitfalls & Errors

The Error //

Hardcoding a downstream service's IP address or hostname directly in application code

// Wrong: breaks the moment this specific instance is rescheduled
const url = "http://10.0.1.47:3000/orders";

// Correct: stable name, resolved dynamically to a healthy instance
const url = "http://order-service/orders";

The Solution //

In any environment where service instances are dynamically created, destroyed, or rescheduled (containers, orchestrated deployments), a hardcoded address becomes stale as soon as the underlying instance changes, causing connection failures. Use a stable DNS name or service registry lookup that's automatically kept current, instead of a fixed address.

The Error //

Registering a service instance in a discovery registry without any accompanying health check

// Wrong: registered, but no way to detect it becomes unhealthy later
registry.register({ name: "order-service", address: myIp });

// Correct: health check gates continued eligibility for traffic
registry.register({ name: "order-service", address: myIp,
  check: { http: "/health", interval: "10s" } });

The Solution //

A registry entry that only tracks whether an instance exists, without verifying it's actually healthy and responsive, can route traffic to an instance that's technically running but broken (e.g. lost its database connection). Health checks must gate whether an instance is eligible to receive traffic, not just whether it's registered.