Distributed Tracing System - System Architecture

High-Level Architecture

┌─────────────────────────────────────────────────────────┐
│              Instrumented Applications                   │
│  (Microservices with Tracing Libraries)                 │
└─────────────────┬───────────────────────────────────────┘
                  │
        ┌─────────▼─────────┐
        │  Tracing Agent    │
        │  (Sidecar/Library)│
        └─────────┬─────────┘
                  │
        ┌─────────▼─────────┐
        │  Trace Collector  │
        │  (Jaeger/OTLP)    │
        └─────────┬─────────┘
                  │
        ┌─────────▼─────────┐
        │  Message Queue    │
        │  (Kafka)          │
        └─────────┬─────────┘
                  │
    ┌─────────────┼─────────────┐
    │             │             │
┌───▼────┐  ┌────▼───┐  ┌─────▼──┐
│Processor│ │Processor│ │Processor│
│ Node 1  │ │ Node 2  │ │ Node 3 │
└───┬────┘  └────┬───┘  └────┬───┘
    │            │           │
    └────────────┴───────────┘
                 │
        ┌────────▼────────┐
        │  Storage Layer  │
        │ (Cassandra/ES)  │
        └────────┬────────┘
                 │
        ┌────────▼────────┐
        │   Query API     │
        │   UI Dashboard  │
        └─────────────────┘

Core Components

Trace Collector

Responsibilities:
- Receive spans from agents
- Validate span data
- Apply sampling decisions
- Buffer and batch spans
- Forward to processing

Span Processor

Processing Pipeline:
1. Validation
2. Enrichment (add metadata)
3. Sampling decision
4. Aggregation
5. Storage write

Storage Layer

Options:
- Cassandra: High write throughput
- Elasticsearch: Rich query capabilities
- ClickHouse: Fast analytics

Chosen: Cassandra + Elasticsearch
- Cassandra for raw spans
- Elasticsearch for queries

This architecture provides scalable, low-latency distributed tracing.