Implement Docker monitoring system addressing isolation level gaps

Co-authored-by: j143 <53068787+j143@users.noreply.github.com>

Author: Copilot

MONITORING.md

@@ -0,0 +1,137 @@
+# Docker Monitoring Implementation
+
+This document describes the monitoring implementation that addresses the "Docker monitoring problem" as referenced in the DataDog blog post.
+
+## Overview
+
+The monitoring system implements multi-level monitoring across three isolation levels:
+
+1. **Process Level** - Individual process monitoring within containers
+2. **Container Level** - Container-specific metrics and isolation monitoring  
+3. **Host Level** - System-wide host metrics and resource monitoring
+
+## Architecture
+
+The monitoring addresses the gap between different isolation levels as described in the monitoring problem:
+
+| Aspect | Process | Container | Host |
+|--------|---------|-----------|------|
+| Spec | Source | Dockerfile | Kickstart |
+| On disk | .TEXT | /var/lib/docker | / |
+| In memory | PID | Container ID | Hostname |
+| In network | Socket | veth* | eth* |
+| Runtime context | server core | host | data center |
+| Isolation | moderate: memory space, etc. | private OS view: own PID space, file system, network interfaces | full: including own page caches and kernel |
+
+## Usage
+
+### Monitor Host Level
+
+```bash
+./basic-docker monitor host
+```
+
+Shows system-wide metrics including:
+- Hostname and uptime
+- Memory usage and availability  
+- CPU count and load average
+- Disk usage
+- Network interfaces (eth*)
+- All containers on the host
+
+### Monitor Process Level
+
+```bash
+./basic-docker monitor process <PID>
+```
+
+Shows process-specific metrics including:
+- Process ID, name, and status
+- Memory usage (RSS and virtual)
+- CPU time and percentage
+- Thread count
+- Open file descriptors
+- Socket information
+
+### Monitor Container Level
+
+```bash
+./basic-docker monitor container <container-id>
+```
+
+Shows container-specific metrics including:
+- Container ID, name, and status
+- Memory usage and limits
+- Network statistics (veth interfaces)
+- Process list within container
+- Namespace information
+- Docker storage path
+
+### Monitor All Levels
+
+```bash
+./basic-docker monitor all
+```
+
+Aggregates metrics from all monitoring levels in a single JSON output.
+
+### Gap Analysis
+
+```bash
+./basic-docker monitor gap
+```
+
+Analyzes monitoring gaps between isolation levels:
+- Process to container correlation gaps
+- Container to host visibility gaps  
+- Cross-level monitoring challenges
+
+### Correlation Analysis
+
+```bash
+./basic-docker monitor correlation <container-id>
+```
+
+Shows correlation between monitoring levels for a specific container, displaying the mapping table and detailed metrics.
+
+## Implementation Details
+
+### Monitors
+
+- `ProcessMonitor` - Reads from `/proc/[pid]/` files to gather process metrics
+- `ContainerMonitor` - Combines process monitoring with container metadata
+- `HostMonitor` - Aggregates system-wide statistics from `/proc/` and `/sys/`
+
+### Metrics Collection
+
+- **Process metrics**: Read from `/proc/[pid]/stat`, `/proc/[pid]/status`, and `/proc/[pid]/fd/`
+- **Container metrics**: Combine process metrics with container directory information
+- **Host metrics**: Read from `/proc/meminfo`, `/proc/loadavg`, `/proc/uptime`, and filesystem stats
+
+### Gap Analysis
+
+The monitoring system identifies three categories of gaps:
+
+1. **Process to Container**: PID mapping, namespace isolation visibility, resource limit enforcement
+2. **Container to Host**: Network isolation vs visibility, filesystem overlay access, resource allocation
+3. **Cross-Level**: Transaction tracing, performance correlation, security event correlation
+
+## Testing
+
+Run monitoring tests:
+
+```bash
+go test -v -run ".*Monitor.*"
+```
+
+Run benchmarks:
+
+```bash
+go test -bench=BenchmarkMonitoring
+```
+
+## References
+
+- [The Docker Monitoring Problem](https://www.datadoghq.com/blog/the-docker-monitoring-problem/)
+- Process isolation and namespace documentation
+- Container runtime specifications