C++ Backend Interview: Web Server Basics, Concurrency, Epoll, and Networking Concepts

The author introduces a C++ backend interview guide, starting with a brief definition of a web server as software that receives client requests, forwards them via HTTP, and serves static or dynamic resources.

Key functions of a web server are listed: request handling, resource management, dynamic content processing, connection management, security/authentication, and logging. Common servers such as Apache, Nginx, and IIS are mentioned.

Concurrency is discussed, noting that the number of simultaneous connections depends on the server's implementation (multithreaded, multiprocess, or asynchronous I/O) and hardware configuration.

Guidelines for configuring a thread pool are provided, emphasizing CPU core count, task type (I/O‑bound vs CPU‑bound), memory limits, and dynamic load monitoring.

The article explains how to combine a thread model with epoll for high‑performance I/O multiplexing: create an epoll instance, add the listening socket, accept new connections in the main thread, assign them to worker threads, and let each worker thread handle its own epoll events.

Important points include keeping the main thread dedicated to accepting connections, giving each worker its own epoll instance, and handling connection management, thread‑pool coordination, and data synchronization.

IO multiplexing concepts are described, highlighting that mechanisms like select , poll , and epoll allow a single thread to monitor many file descriptors, reducing the need for many threads or processes.

Edge‑triggered (ET) and level‑triggered (LT) modes of epoll are compared: ET notifies only on state changes and requires non‑blocking handling, while LT continues to report readiness until the condition is cleared, making it suitable for blocking workflows.

Common HTTP methods (GET, POST, PUT, DELETE, PATCH, HEAD, OPTIONS) and the differences between GET and POST are outlined, along with a breakdown of URL components and the role of URI.

Thread‑pool communication mechanisms such as task queues, synchronization primitives, callbacks, semaphores, and shared memory are summarized.

C++ type conversion techniques are reviewed, covering implicit conversion and explicit casts: static_cast , dynamic_cast , const_cast , and reinterpret_cast .

The differences between heap and stack allocation, and between pointers and references, are explained.

Usage of the static keyword is illustrated with examples of static local variables, static member variables, and static member functions, each wrapped in ... blocks.

Debugging a web server is addressed with steps such as checking logs, validating input data, using breakpoints, handling exceptions, reviewing code logic, verifying environment configuration, writing test cases, and employing profiling tools.

Basic gdb commands for multi‑threaded debugging are listed, including compilation with -g , setting breakpoints, following forked processes, and switching between threads.

The Linux ping utility is described for checking host reachability, measuring RTT, packet loss, TTL, and performing basic network topology analysis.

Implementation details of ping are outlined: creating a raw socket, building ICMP packets, setting IP headers, computing checksums, sending requests, and processing replies.

Behavior of std::map when accessing a missing key with the [] operator is clarified: it inserts a default‑constructed value.

Common TCP programming APIs in C/C++ are enumerated: socket() , bind() , listen() , accept() , connect() , send() / sendto() , recv() / recvfrom() , and close() .

The three‑way TCP handshake and four‑way termination sequences are explained step by step.

When a URL is entered, the typical workflow—DNS resolution, TCP connection establishment, HTTP request transmission, server processing, HTTP response receipt, and client rendering—is summarized.

Potential deadlocks in server development are discussed, with mitigation strategies such as reducing lock count, applying consistent lock ordering, setting timeouts, and using detection tools.

Differences between HTTP and HTTPS are highlighted, focusing on encryption, default ports, data confidentiality, and the role of Certificate Authorities in establishing trust.