SPRINT 5 SYSTEMS INTEGRATION PROJECTS

Systems Integration: Learning Through Building

This is an excellent sprint topic. Systems Integration is where theory meets reality—it’s the domain of “why does this work in development but crash in production?” These projects will force you to confront integration failure points directly.

Core Concept Analysis

The topics break down into these fundamental building blocks:

Concept Cluster	What You Need to Internalize
Resource Handles	File descriptors, sockets, and other OS handles are just integers—but they represent real, limited resources that can leak, exhaust, or become invalid
Blocking Boundaries	Every I/O operation has a decision point: wait or return immediately? This shapes your entire program architecture
Error Propagation	Syscalls fail in specific, documented ways. The integration point between your code and the kernel is a contract you must honor
Signals	Asynchronous interrupts that can happen anywhere. The OS poking your process when you least expect it
Memory Layers	Your allocator sits between you and the OS; mmap bypasses it entirely. Cache effects mean “faster code” isn’t always faster
Failure Under Stress	Systems don’t degrade gracefully by default—they cliff-dive. You must engineer resilience

Project 1: Multi-Source Log Tailer with Rotation Handling

File: SPRINT_5_SYSTEMS_INTEGRATION_PROJECTS.md
Programming Language: C
Coolness Level: Level 2: Practical but Forgettable
Business Potential: 3. The “Service & Support” Model
Difficulty: Level 3: Advanced
Knowledge Area: Systems Programming / File I/O
Software or Tool: File Descriptors / Inodes
Main Book: “The Linux Programming Interface” by Michael Kerrisk

What you’ll build: A tool that simultaneously watches multiple log files (like /var/log/syslog, application logs, etc.), aggregates their output to stdout with source labels, and correctly handles log rotation without missing lines or duplicating content.

Why it teaches Systems Integration: Log rotation is the perfect integration failure case. When logrotate moves app.log to app.log.1 and creates a new app.log, your file descriptor still points to the old file! You’ll learn that an FD is a handle to an inode, not a path. This project forces you to:

Manage multiple file descriptors simultaneously
Detect when a file has been rotated (stat comparison, inode changes)
Handle blocking reads on files that may not have new content
Deal with partial lines at file boundaries

Core challenges you’ll face:

FD vs Path confusion: Your FD keeps reading the old rotated file while the path now points to a new file (maps to: file descriptors as OS handles)
Blocking on empty files: read() on a regular file returns 0 at EOF but doesn’t block—you need to poll/sleep (maps to: blocking vs non-blocking behavior)
Detecting rotation: Using fstat() + stat() to compare inodes and detect when to reopen (maps to: syscall usage, reading manpages)
Resource cleanup: Properly closing FDs when files disappear or are rotated (maps to: OS resources as handles)

Difficulty: Intermediate Time estimate: 1-2 weeks Prerequisites: Basic C, familiarity with open/read/close syscalls

Real world outcome: Run your tool pointing at 3-4 log files. Trigger log rotation (manually or via logrotate -f). Your tool should seamlessly continue reading from the new files without missing lines or duplicating content. You’ll see interleaved, labeled output from all sources.

Key Concepts:

File descriptors and inodes: “The Linux Programming Interface” by Michael Kerrisk (Ch. 4-5) - definitive explanation of FDs, inodes, and the VFS layer
Non-blocking I/O on files: “Advanced Programming in the UNIX Environment” by Stevens & Rago (Ch. 14) - covers poll/select and non-blocking file I/O
The stat() family: man 2 stat - you’ll read this manpage many times

Learning milestones:

Single file tail working → You understand basic FD lifecycle (open, read, close)
Multiple files with select/poll → You understand multiplexing I/O across multiple FDs
Rotation detection working → You’ve internalized that FDs reference inodes, not paths
Graceful handling of deleted files → You understand ENOENT, stale handles, and defensive syscall error checking

Project 2: HTTP Connection Pool with Failure Injection

File: SPRINT_5_SYSTEMS_INTEGRATION_PROJECTS.md
Programming Language: C
Coolness Level: Level 3: Genuinely Clever
Business Potential: 4. The “Open Core” Infrastructure
Difficulty: Level 3: Advanced
Knowledge Area: Networking / Resilience
Software or Tool: Sockets / Connection Pools
Main Book: “Release It!” by Michael Nygard

What you’ll build: A library/tool that maintains a pool of persistent HTTP connections to a server, reuses them for multiple requests, handles connection failures gracefully, and includes a “chaos mode” that randomly closes connections to test resilience.

Why it teaches Systems Integration: This project sits at the intersection of networking (sockets), resource management (pooled FDs), error handling (connection refused, reset, timeout), and failure modes. You’ll see exactly how systems fall apart under stress and build intuition for defensive programming.

Core challenges you’ll face:

Socket FD exhaustion: Open too many connections and hit ulimit -n (maps to: FD limits, OS resources as handles)
Half-open connections: Server closed the connection but you haven’t read from it yet—next write succeeds, next read fails with RST (maps to: syscall error handling, ECONNRESET)
Blocking connect(): Connection to unresponsive server blocks forever without timeout (maps to: blocking vs non-blocking behavior)
Detecting dead connections: How do you know a pooled connection is still valid without sending data? (maps to: failure modes, TCP keepalive)
Graceful degradation: What happens when the server is slow? Do you spawn infinite connections? (maps to: failure modes under load)

Difficulty: Intermediate-Advanced Time estimate: 2-3 weeks Prerequisites: Basic networking (TCP concepts), C sockets basics

Real world outcome:

Run your connection pool against a local HTTP server
Inject failures (kill server, restart, network partition simulation)
Watch your pool detect dead connections, clean them up, and establish new ones
Run with chaos mode enabled and see your pool self-heal
Measure: connections reused, connections dropped, requests failed

Key Concepts:

Socket programming fundamentals: “TCP/IP Sockets in C” by Donahoo & Calvert - concise, practical socket programming
TCP state machine and failure modes: “TCP/IP Illustrated, Vol. 1” by Stevens (Ch. 18-19) - understanding RST, FIN, half-open states
Non-blocking sockets and poll(): “The Linux Programming Interface” by Kerrisk (Ch. 63) - I/O multiplexing
Error codes: man 2 connect, man 2 read, man 2 write - you’ll memorize EAGAIN, ECONNREFUSED, ECONNRESET, EPIPE

Learning milestones:

Basic pool working → You can reuse connections, understand socket lifecycle
Timeout handling working → You understand non-blocking connect + select/poll
Failure detection working → You understand TCP half-open states and how to detect dead connections
Chaos mode survives → You’ve built resilient code that handles failure as a normal condition

Project 3: Process Supervisor with Signal Forwarding

File: SPRINT_5_SYSTEMS_INTEGRATION_PROJECTS.md
Programming Language: C
Coolness Level: Level 4: Hardcore Tech Flex
Business Potential: 3. The “Service & Support” Model
Difficulty: Level 3: Advanced
Knowledge Area: Systems Programming / Process Management
Software or Tool: Signals / Fork-Exec
Main Book: “Advanced Programming in the UNIX Environment” by Stevens & Rago

What you’ll build: A supervisor daemon that launches and monitors child processes, restarts them if they crash, forwards signals (SIGTERM, SIGHUP) to children, and handles zombie reaping correctly. Like a minimal supervisord or systemd for a single service.

Why it teaches Systems Integration: This project is pure systems integration—your supervisor sits between the OS and the supervised process, translating signals and managing process lifecycle. You’ll encounter every classic Unix process gotcha: zombies, orphans, signal races, and FD inheritance.

Core challenges you’ll face:

Zombie processes: Child exits but you don’t wait()—it stays in process table forever (maps to: OS resources as handles)
Signal forwarding: You receive SIGTERM, need to forward to child, then exit yourself—order matters! (maps to: signals)
Race conditions: Child exits between your check and your signal—you signal a dead/recycled PID (maps to: failure modes)
FD inheritance: Child inherits all your open FDs unless you’re careful (maps to: file descriptors)
The SIGCHLD dance: Handling SIGCHLD correctly while also handling other signals (maps to: signal handling complexity)

Difficulty: Intermediate-Advanced Time estimate: 2-3 weeks Prerequisites: fork/exec basics, basic signal concepts

Real world outcome:

Run supervisor with a simple script that crashes after 5 seconds
Watch supervisor automatically restart it
Send SIGTERM to supervisor, watch it gracefully terminate child first
Send SIGHUP to supervisor, watch it forward to child (for config reload)
Kill child with SIGKILL, watch supervisor detect and restart

Key Concepts:

Process creation and lifecycle: “Advanced Programming in the UNIX Environment” by Stevens & Rago (Ch. 8-9) - fork, exec, wait, and all their variants
Signal handling: “The Linux Programming Interface” by Kerrisk (Ch. 20-22) - the definitive guide to signals in Linux
Zombie processes and orphans: “Operating Systems: Three Easy Pieces” (Process API chapter) - conceptual foundation

Learning milestones:

Fork/exec/wait cycle working → You understand basic process lifecycle
Automatic restart working → You understand SIGCHLD and wait() status inspection
Signal forwarding working → You understand signal handlers, async-signal-safety
No zombies, no races → You’ve internalized defensive process management

Project 4: Memory-Mapped Ring Buffer IPC

File: SPRINT_5_SYSTEMS_INTEGRATION_PROJECTS.md
Programming Language: C
Coolness Level: Level 5: Pure Magic (Super Cool)
Business Potential: 4. The “Open Core” Infrastructure
Difficulty: Level 4: Expert
Knowledge Area: IPC / High Performance Computing
Software or Tool: Shared Memory / mmap
Main Book: “The Linux Programming Interface” by Michael Kerrisk

What you’ll build: An inter-process communication system using a memory-mapped file as a ring buffer. One process writes log entries, another reads them—without traditional socket/pipe IPC, just shared memory.

Why it teaches Systems Integration: This project exposes the allocator/OS boundary directly. You’re bypassing malloc entirely and working with raw pages from the OS. You’ll understand how memory-mapped files work, why cache effects matter for shared memory, and how to coordinate access without the kernel’s help.

Core challenges you’ll face:

Page alignment: mmap works in pages, not bytes—your data structures must respect this (maps to: interaction between allocator + OS)
Cache coherency: Two processes accessing shared memory—when do writes become visible? (maps to: cache effects)
Synchronization without syscalls: Using atomics or spinlocks in shared memory (maps to: understanding what the OS does vs. doesn’t do for you)
Cleanup on crash: What happens to the mapped file if writer crashes mid-write? (maps to: failure modes)
msync() semantics: When does data actually hit disk? (maps to: syscall behavior, blocking)

Difficulty: Advanced Time estimate: 2-3 weeks Prerequisites: Pointers, basic understanding of memory layout, atomic operations concept

Real world outcome:

Run writer process that logs 100k messages/second to ring buffer
Run reader process that tails the buffer in real-time
Kill writer, restart it—reader continues from where it left off
Observe memory usage: no copies, data stays in kernel page cache
Measure: throughput should be 10-100x faster than socket IPC

Key Concepts:

Memory-mapped files: “The Linux Programming Interface” by Kerrisk (Ch. 49) - mmap(), msync(), and shared mappings
Memory ordering and atomics: “C++ Concurrency in Action” by Williams (Ch. 5) or “Rust Atomics and Locks” by Mara Bos - even if you’re writing C, these explain the concepts best
Ring buffer design: “Disruptor technical paper” by LMAX - the definitive high-performance ring buffer design

Learning milestones:

Basic mmap working → You can create and access memory-mapped files
Ring buffer logic working → You understand how to structure data for shared access
Multi-process access working → You understand memory visibility between processes
Crash recovery working → You understand msync, file-backed durability

Project 5: “Works On My Machine” Debugger

File: SPRINT_5_SYSTEMS_INTEGRATION_PROJECTS.md
Programming Language: C
Coolness Level: Level 3: Genuinely Clever
Business Potential: 3. The “Service & Support” Model
Difficulty: Level 3: Advanced
Knowledge Area: Systems Troubleshooting / Linux Internals
Software or Tool: /proc Filesystem
Main Book: “How Linux Works, 3rd Edition” by Brian Ward

What you’ll build: A diagnostic tool that captures a “machine fingerprint” of the execution environment and compares it between systems. It detects differences in: file descriptor limits, environment variables, file permissions, library versions, kernel parameters, and available resources that cause cross-machine failures.

Why it teaches Systems Integration: This is meta—you’re building a tool to debug the exact class of bugs this sprint is about. You’ll learn what environmental factors actually matter by cataloging them systematically. When something works locally but fails in CI/prod, you’ll know exactly where to look.

Core challenges you’ll face:

Discovering what matters: What system state actually affects program behavior? (maps to: understanding integration points)
Reading /proc and /sys: Linux exposes everything as files—learning to read them (maps to: file descriptors, syscalls)
Resource limit detection: getrlimit(), /proc/self/limits, and how they affect your program (maps to: OS resources)
Library version detection: ldd, /proc/self/maps, dlopen behavior differences (maps to: cross-layer debugging)
Environment sanitization: What environment variables can break a program? (maps to: “works on my machine” bugs)

Difficulty: Intermediate Time estimate: 1-2 weeks Prerequisites: Basic C, familiarity with Linux filesystem

Real world outcome:

Run ./diagtool capture > local.json on your machine
Run same on CI/server, get server.json
Run ./diagtool diff local.json server.json
See exactly what’s different: “ULIMIT_NOFILE: 1024 vs 65535”, “LD_LIBRARY_PATH: set vs unset”
Instantly identify why your program fails remotely

Key Concepts:

The /proc filesystem: “How Linux Works” by Brian Ward (Ch. 8) - understanding /proc as window into kernel state
Resource limits: man 2 getrlimit, man 5 limits.conf - the classic source of “works on my machine”
Dynamic linking: “Computer Systems: A Programmer’s Perspective” by Bryant & O’Hallaron (Ch. 7) - how libraries are loaded

Learning milestones:

Basic fingerprint capture working → You know what system state to inspect
Diff detection working → You can pinpoint environmental differences
Used it to debug a real issue → You’ve internalized that “the environment is part of the system”

Project Comparison Table

Project	Difficulty	Time	Depth of Understanding	Fun Factor	Primary Concepts
Multi-Source Log Tailer	Intermediate	1-2 weeks	⭐⭐⭐	⭐⭐⭐	FDs, blocking I/O, inode vs path
HTTP Connection Pool	Intermediate-Advanced	2-3 weeks	⭐⭐⭐⭐	⭐⭐⭐⭐	Sockets, failure modes, non-blocking
Process Supervisor	Intermediate-Advanced	2-3 weeks	⭐⭐⭐⭐	⭐⭐⭐	Signals, process lifecycle, zombies
Memory-Mapped Ring Buffer	Advanced	2-3 weeks	⭐⭐⭐⭐⭐	⭐⭐⭐⭐	mmap, cache effects, allocator bypass
“Works On My Machine” Debugger	Intermediate	1-2 weeks	⭐⭐⭐	⭐⭐⭐⭐⭐	/proc, resource limits, env debugging

Recommended Progression

Based on the sprint goals, here’s the recommended sequence:

Start with: Multi-Source Log Tailer (Week 1-2)

This is the gentlest on-ramp. You’ll immediately encounter the FD/inode distinction, learn to read stat(2) manpages, and build intuition for “the OS sees things differently than your code does.” It’s satisfying—you’ll have a useful tool at the end.

Then: Process Supervisor (Week 2-4)

This takes you into signal handling territory—the most “integration-y” part of Unix programming. Signals are where the OS interrupts your program asynchronously, and handling them correctly requires careful thinking about system state. You’ll also solidify fork/exec/wait understanding.

Then: HTTP Connection Pool (Week 4-6)

Now you’re ready for networking complexity. This project combines FDs (sockets), blocking/non-blocking behavior, and failure modes under load. The “chaos mode” requirement forces you to think about resilience from the start.

Optional depth: Memory-Mapped Ring Buffer

If you have extra time and want to go deeper on the allocator/OS boundary and cache effects, this project delivers. It’s harder but teaches concepts you can’t learn any other way.

Keep handy: “Works On My Machine” Debugger

Build this whenever you hit your first cross-machine bug during the other projects. It’s most valuable when you have a real debugging need.

Final Integration Project: Deployment Pipeline Tool

What you’ll build: A tool that watches a source directory for changes, synchronizes files to a remote target (via SSH/rsync), restarts a supervised service when deployment completes, aggregates logs from the deployed service, and reports deployment status—all with proper failure handling and graceful degradation.

Why this integrates everything:

Log Tailer component: Watch and aggregate logs from deployed service
Process Supervisor component: Manage the deployed service lifecycle
Connection Pool component: Maintain SSH connection for efficient file sync
Environment Debugger component: Compare local dev vs remote production environment
Memory-Mapped component (optional): Use mmap for efficient file comparison/checksum

Core challenges you’ll face:

Cascading failures: SSH connection dies during file sync—what state is the remote in? (maps to: failure modes at integration points)
Coordinating multiple subsystems: File sync complete → restart service → wait for healthy → start log aggregation (maps to: cross-layer orchestration)
Signal handling across processes: SIGTERM should stop deployment gracefully, finish current operations, clean up (maps to: signals)
Resource management: Long-running tool must not leak FDs, connections, memory (maps to: OS resources as handles)
The “partial deployment” problem: What if you synced half the files and crashed? (maps to: transactional thinking)

Difficulty: Advanced Time estimate: 3-4 weeks Prerequisites: Completion of at least 3 projects above

Real world outcome:

Run ./deployer watch ./src remote:~/app
Edit a file locally, watch it sync and service restart automatically
See aggregated logs from the remote service in your terminal
Kill deployer with Ctrl+C, watch graceful shutdown
Run ./deployer diff ./src remote:~/app to see what’s different
This becomes your actual deployment tool for small projects

Key Concepts: This project synthesizes all previous learning. No new concepts—just integration.

Learning milestones:

Basic watch+sync working → Core file monitoring and transfer
Service restart integration working → Coordinating sync completion with process management
Log aggregation working → Full observability into deployed system
Graceful failure handling working → You’ve built a resilient system, not just working code
Actually using it for a project → You trust your systems programming skills

Core Mental Model

Real systems fail at integration points, not in isolation.

This progression builds your “systems integration intuition”—the ability to look at a bug and immediately suspect the integration point rather than the code logic. That mental model will serve you for your entire career.