5 exercises — load balancer, TCP vs UDP, DNS, HTTP status codes, CDN — the networking concepts that appear in every architecture discussion and incident review.
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"The service is behind a load balancer — requests are distributed across three backend instances." What does a load balancer do?
A load balancer sits in front of a group of servers and routes each incoming request to one of them — using round-robin, least-connections, or IP hash algorithms. This improves availability (if one server fails, the others keep serving) and scalability (add more servers behind the balancer to handle more traffic). Common examples: AWS ALB/NLB, NGINX, HAProxy.
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"We use TCP for the payment API and UDP for the live video stream." Why this choice?
TCP (Transmission Control Protocol) establishes a connection (3-way handshake), ensures packets arrive in order, retransmits lost packets, and controls congestion. Ideal for accuracy-critical traffic: APIs, file transfers, email. UDP (User Datagram Protocol) just fires packets — no connection, no acknowledgment, no retransmit. Ideal for latency-sensitive real-time data: video/audio streaming, gaming, DNS lookups, where a stale retransmit would be worse than a dropped frame.
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"The browser can't resolve the hostname — it looks like the _____ server is not responding." Which service translates domain names to IP addresses?
DNS (Domain Name System) is the internet's phone book. When you type api.example.com, your OS queries a DNS resolver, which recursively looks up the authoritative name server for example.com and returns its IP address. Without DNS, you'd need to memorise IP addresses — DNS outages can take down services even when servers are healthy. Common tools: dig api.example.com, nslookup.
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"The API returned a 429 status code." What does this mean and what should the client do?
429 Too Many Requests means the client hit the server's rate limit — too many requests in a given time window. The response often includes a Retry-After header indicating how long to wait. Best practice: implement exponential backoff with jitter — double the wait time on each retry, plus a small random offset to avoid a "thundering herd" when all clients retry simultaneously. Other key codes: 200 OK, 201 Created, 400 Bad Request, 401 Unauthorized, 403 Forbidden, 404 Not Found, 500 Internal Server Error, 503 Service Unavailable.
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"We're migrating traffic to the CDN edge — static assets will be served from a location close to the user." What does CDN stand for and how does it work?
A CDN (Content Delivery Network) stores copies of static assets (images, JS, CSS, video) at edge nodes around the world. When a user in Kyiv requests an image, they get it from the nearest edge node (say, Warsaw) rather than your origin server in Virginia — dramatically reducing latency. CDNs also absorb traffic spikes, protect against DDoS, and improve cache hit rates. Popular CDNs: Cloudflare, AWS CloudFront, Fastly, Akamai.
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Sarah from the DevOps team just posted this comment on your code review: 'The latency between our API endpoint and the database server is consistently high. I've checked network diagnostics – it seems there's significant packet loss on the eth0 interface.' What does 'packet loss' likely indicate in this context?
Packet loss refers to instances where network packets fail to reach their destination. This often indicates a physical layer issue – problems like faulty cables, congested network segments, or interference – that disrupt the reliable transmission of data. Option A and C are potential causes for high latency but don't directly address packet loss; Option D is about database performance, not network connectivity.
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Mark in the Slack channel #dev-ops asks: 'Hey team, we're seeing a spike in requests to our user authentication service. The response times are degrading significantly. What protocol are we *primarily* using for this communication?'
gRPC is a popular choice for microservices communication due to its performance and efficiency. While TLS/SSL provides security, it's not the primary protocol governing data transfer itself. HTTP/2 focuses on improving web delivery, and UDP is best suited for scenarios like live video streaming where low latency is paramount – this isn't relevant here. gRPC leverages Protocol Buffers for efficient serialization.
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curl -I https://api.example.com/users/123
During a code review, you notice the build process failing intermittently with errors related to network timeouts. A teammate suggests investigating potential issues with DNS resolution. Which of the following best explains why this might be occurring?
The question focuses on DNS resolution. A timeout during a network request often indicates that the client cannot successfully translate a domain name into an IP address. This is precisely what a DNS resolver does – it's a fundamental part of how the internet works and a common source of network issues. Options C and D describe other potential causes, but don't directly relate to the core problem presented by the timeout.
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David: 'I'm getting a `Connection Refused` error when trying to connect to the staging server. I checked my firewall rules and everything seems fine. What could be causing this?' Considering common networking issues, which of the following is MOST likely?
A `Connection Refused` error indicates that the target host actively refused the connection attempt. This most commonly points to the server itself being unavailable – perhaps it's down due to an outage or maintenance. While DNS issues or load balancer problems can *lead* to connection failures, they wouldn't directly result in a 'refused' message. A damaged cable would likely manifest differently.
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Emily (in a Slack channel) asks: 'We're experiencing high latency when fetching data from the microservice. The logs show many `HTTP 504 Gateway Timeout` errors. What does this typically signify in terms of network protocols?',
An `HTTP 504 Gateway Timeout` indicates that the server acting as a gateway (in this case, likely an API gateway or reverse proxy) didn't receive a response from the upstream server within the configured timeout period. This strongly suggests the *upstream* service is taking too long to respond—a common issue related to performance bottlenecks or network delays between them. It doesn't necessarily mean the client-side code is at fault.
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During a PR review, you see the following comment: 'The service is intermittently failing to connect to external APIs. The error messages suggest potential issues with SSL/TLS handshakes. What protocol component is most directly involved here?'
SSL/TLS handshakes are the process of establishing a secure connection between two parties using cryptographic protocols. This involves exchanging keys and verifying identities – all handled through HTTP headers (like `Host` for domain identification and `User-Agent` for client information). IP addresses and TCP/IP sockets are foundational but don't directly participate in the security handshake itself.
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You're debugging a failing API request. The response code is `502 Bad Gateway`. Considering this error and common causes, which of the following actions would be MOST appropriate for initial investigation?
A `502 Bad Gateway` error signifies that the API gateway received an invalid response from an upstream server. The firewall is a primary suspect here – it could be blocking traffic or introducing delays. While investigating timeouts and client connectivity are important, the immediate focus should be on ensuring the upstream service is reachable and functioning correctly.
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Mark: 'We're deploying a new feature that requires frequent communication with a third-party service. What network protocol choice would be most suitable for this scenario, considering factors like reliability and efficiency?'
TCP is the most appropriate choice here due to its reliability features—guaranteed delivery, error detection and correction, and flow control. This ensures that data transmitted between services is delivered accurately and without loss, which is crucial for frequent communication where data integrity is paramount. UDP would be unsuitable due to its unreliability.
What does the "Networking & Protocols Vocabulary" vocabulary exercise cover?
This exercise tests real IT vocabulary related to networking & protocols vocabulary through 13 multiple-choice questions, each built from realistic workplace sentences rather than abstract definitions.
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