Key Insights
# Thread-safe logging prevents a log soup When microservices spin up dozens of threads, logging without locks is like letting ten chefs scribble in the same cookbook—you get garbled recipes. A mutex around your write call enforces one-pen rule, preserving order and readability. # Structured logs + correlation IDs Modern microservices prefer JSON logs with fields like timestamp, level, service, and correlationId. This lets you stitch traces across services using dashboards or tools like Elasticsearch or Pinecone. ## Common Misunderstandings # Mutex kills performance? Spoiler: a brief lock around I/O is negligible. Unless you’re logging in millions-per-second loops, you’ll barely notice. Panicking without numbers? Premature optimization writes bad logs. # Library thread safety vs destination safety Even if Logrus or Winston lock internally, your actual writer (file, stdout, socket) can become the weak link if shared. Wrap it yourself if in doubt. # Logging as an afterthought Teams ship features and drop in console.log, forgetting structure and context. Later, scaling bites you with “I can’t read this trash” syndrome. ## Current Trends # Template-driven machine-readable formats JSON/NDJSON templates enforce consistent fields, making your logs spoon-feed tools instead of chewing your time. # Distributed tracing and context propagation Trace IDs, service names, and tags need to travel across queues, HTTP calls, and background jobs. This is how you map an entire request journey. # Batch, async, aggregate To avoid blocking, loggers buffer messages and flush asynchronously to systems like Loki or third-party SaaS. This decouples your app’s speed from I/O latency. ## Real-World Examples # C++ Mutex-Guarded Logger
std::mutex logMutex;
void log(const std::string &msg) {
std::lock_guard<std::mutex> guard(logMutex);
logfile << msg << std::endl;
}# Node.js with Correlation IDs
app.use((req, res, next) => {
req.correlationId = req.headers['x-correlation-id'] || uuidv4();
logger.defaultMeta = { ...logger.defaultMeta, correlationId: req.correlationId };
res.setHeader('x-correlation-id', req.correlationId);
next();
});# Go Logrus Threadsafe Writer
type TSWriter struct { w io.Writer; mu *sync.Mutex }
func (t TSWriter) Write(p []byte) (int, error) {
t.mu.Lock(); defer t.mu.Unlock()
return t.w.Write(p)
}
logrus.SetOutput(TSWriter{w: os.Stdout, mu: &sync.Mutex{}})Ready to stop your logs looking like ransom notes, or are you up for nightly debugging sessions? —Chandler Bing
