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Quiz

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Load Balancer

Q1. What role does Nginx play in this hands-on?

  • A. It acts as a service registry, tracking which gateway replicas are alive
  • B. It terminates TLS and decrypts HTTPS traffic before forwarding to the gateway
  • C. It is a Layer 7 reverse proxy and load balancer that receives all external traffic (host port 8080, Nginx's port 80) and distributes it across gateway replicas
  • D. It replaces the gateway service, routing directly to microservices
Answer

C — L7 reverse proxy and load balancer.

Nginx sits at the edge: all external traffic arrives at Nginx (the lb service, host port 8080 → port 80). It inspects the HTTP request and forwards it to one of the gateway replicas based on the configured algorithm. The gateway replicas have no exposed ports — they are only reachable from within the Docker network through Nginx.

Q2. What does least_conn in the Nginx upstream block configure?

  • A. The minimum number of healthy connections required before the upstream is used
  • B. The load balancing algorithm — each new request goes to the backend with the fewest active connections
  • C. The maximum number of simultaneous connections Nginx accepts from clients
  • D. The least-recently-used eviction policy for upstream connection caches
Answer

B — Fewest active connections algorithm.

With least_conn, Nginx tracks how many requests are currently being processed by each gateway replica and routes the next request to the one with the smallest count. This is better than round-robin for requests with variable duration — it prevents a slow replica from accumulating a backlog.

Q3. After scaling the gateway to 5 replicas, why must Nginx be reloaded?

  • A. Nginx caches HTTP responses and must flush the cache when backends change
  • B. Scaling creates new Docker networks that Nginx cannot detect automatically
  • C. Nginx resolves gateway DNS once at startup and caches all returned IPs; a reload forces re-query of Docker DNS to discover the new replica IPs
  • D. The new replicas use different ports that Nginx must be configured to accept
Answer

C — DNS resolved once at startup; reload forces re-query.

Nginx's upstream block resolves the gateway hostname when the worker processes start and caches the resulting IP addresses. When you scale to 5 replicas, Docker assigns new IPs to the new containers, but Nginx still uses the original 3 IPs from startup. Running nginx -s reload causes Nginx to re-resolve gateway, discovering all 5 IPs.