# Docker Socket Permissions and Security

This document covers the security considerations and configuration options for Docker socket access in Zastava Agent deployments.

## Overview

The Zastava Agent requires read access to the Docker socket (`/var/run/docker.sock`) to:

1. **Monitor container lifecycle events** - Start, stop, pause, die, etc.
2. **Inspect running containers** - Image digest, labels, environment variables
3. **Collect runtime evidence** - Loaded libraries, process information

## Default Configuration

By default, the agent runs as:
- **User:** `zastava-agent` (system user)
- **Group:** `docker` (grants socket access)
- **Socket:** `/var/run/docker.sock`

```yaml
# systemd service configuration
User=zastava-agent
Group=docker
ReadWritePaths=/var/run/docker.sock
```

## Security Considerations

### Docker Socket Exposure Risks

The Docker socket provides significant privileges:

| Capability | Risk Level | Mitigation |
|------------|-----------|------------|
| List containers | Low | Required for operation |
| Inspect containers | Low | Required for operation |
| Read container logs | Medium | Agent does not use this |
| Create containers | High | Agent does not use this |
| Execute in containers | Critical | Agent does not use this |
| Pull images | High | Agent does not use this |
| Remove containers | High | Agent does not use this |

### Agent Behavior

The Zastava Agent performs **read-only operations**:

```go
// Operations used by agent
docker.ContainerList(...)     // List running containers
docker.ContainerInspect(...)  // Get container details
docker.Events(...)            // Subscribe to lifecycle events
```

The agent **does not** perform write operations such as creating, starting, stopping, or removing containers.

## Alternative Configurations

### Option 1: Docker API Proxy (Recommended for High-Security)

Deploy a Docker API proxy that restricts available operations:

```yaml
# docker-proxy configuration example
allowed_endpoints:
  - "GET /containers/json"        # List containers
  - "GET /containers/*/json"      # Inspect container
  - "GET /events"                 # Subscribe to events
  - "GET /_ping"                  # Health check
```

Example proxy: [Tecnativa/docker-socket-proxy](https://github.com/Tecnativa/docker-socket-proxy)

```bash
# Deploy proxy
docker run -d \
  --name docker-proxy \
  -v /var/run/docker.sock:/var/run/docker.sock:ro \
  -e CONTAINERS=1 \
  -e EVENTS=1 \
  -p 2375:2375 \
  tecnativa/docker-socket-proxy
```

Configure agent to use proxy:
```env
ZASTAVA_AGENT__DockerEndpoint=tcp://localhost:2375
```

### Option 2: Unix Socket with ACLs

Use filesystem ACLs for fine-grained access:

```bash
# Install ACL support
sudo apt-get install acl

# Set ACL for zastava-agent user
sudo setfacl -m u:zastava-agent:rw /var/run/docker.sock

# Verify ACL
getfacl /var/run/docker.sock
```

This allows removing the user from the `docker` group while maintaining socket access.

### Option 3: SELinux/AppArmor Policies

#### SELinux Policy

```te
# zastava-agent.te
module zastava_agent 1.0;

require {
    type docker_var_run_t;
    type zastava_agent_t;
    class sock_file { read write };
}

# Allow read/write to Docker socket
allow zastava_agent_t docker_var_run_t:sock_file { read write getattr };
```

#### AppArmor Profile

```apparmor
# /etc/apparmor.d/zastava-agent
profile zastava-agent /opt/stellaops/zastava-agent/StellaOps.Zastava.Agent {
  # Docker socket access
  /var/run/docker.sock rw,

  # Deny network access except to scanner backend
  network inet stream,
  network inet6 stream,

  # Read-only system access
  /etc/stellaops/* r,
  /opt/stellaops/zastava-agent/** mr,

  # Data directory
  /var/lib/zastava-agent/** rw,
}
```

### Option 4: Rootless Docker

For maximum isolation, use rootless Docker:

```bash
# Install rootless Docker
dockerd-rootless-setuptool.sh install

# Configure agent to use rootless socket
export ZASTAVA_AGENT__DockerEndpoint=unix:///run/user/1000/docker.sock
```

Note: Rootless Docker has some limitations with networking and storage drivers.

## Log Paths

### Agent Logs

| Component | Log Location |
|-----------|--------------|
| Agent stdout/stderr | `journalctl -u zastava-agent` |
| Runtime events | `/var/lib/zastava-agent/runtime-events/*.ndjson` |
| Health check | Agent stdout (structured JSON) |

### Log Configuration

```env
# Set log level
Serilog__MinimumLevel__Default=Information

# Available levels: Verbose, Debug, Information, Warning, Error, Fatal
```

### Log Rotation

Event buffer files are automatically rotated:

```yaml
# Default settings
event_buffer:
  max_file_size_mb: 10
  max_total_size_mb: 100
  retention_hours: 24
```

## Health Check Configuration

The agent exposes HTTP health endpoints:

| Endpoint | Port | Description |
|----------|------|-------------|
| `/healthz` | 8080 | Liveness probe |
| `/readyz` | 8080 | Readiness probe |
| `/livez` | 8080 | Alias for liveness |

### Health Check Port

Configure via environment variable:

```env
ZASTAVA_AGENT__HealthCheck__Port=8080
```

### Health Check Behavior

**Liveness (`/healthz`):**
- Returns 200 if agent process is running
- Returns 503 if critical subsystems failed

**Readiness (`/readyz`):**
- Returns 200 if agent can process events
- Returns 503 if:
  - Docker socket is unreachable
  - Event buffer is not writable
  - Backend connection failed

### Prometheus Metrics

Health metrics are exposed at `/metrics`:

```
# HELP zastava_agent_docker_connected Docker connectivity status
# TYPE zastava_agent_docker_connected gauge
zastava_agent_docker_connected 1

# HELP zastava_agent_buffer_writable Event buffer writability
# TYPE zastava_agent_buffer_writable gauge
zastava_agent_buffer_writable 1

# HELP zastava_agent_events_buffered Number of events in buffer
# TYPE zastava_agent_events_buffered gauge
zastava_agent_events_buffered 42
```

## Monitoring Recommendations

### Alerting Rules

```yaml
groups:
  - name: zastava-agent
    rules:
      - alert: ZastavaAgentDown
        expr: up{job="zastava-agent"} == 0
        for: 5m
        annotations:
          summary: "Zastava Agent is down on {{ $labels.instance }}"

      - alert: ZastavaDockerDisconnected
        expr: zastava_agent_docker_connected == 0
        for: 1m
        annotations:
          summary: "Zastava Agent lost Docker connectivity"

      - alert: ZastavaBufferNotWritable
        expr: zastava_agent_buffer_writable == 0
        for: 1m
        severity: critical
        annotations:
          summary: "Zastava event buffer is not writable"
```

### Grafana Dashboard

Import the Zastava monitoring dashboard from:
`docs/modules/zastava/operations/dashboards/zastava-observability.json`

## Troubleshooting

### Cannot Access Docker Socket

```bash
# Check socket exists
ls -la /var/run/docker.sock

# Check agent user groups
id zastava-agent

# Check Docker daemon is running
systemctl status docker

# Test socket access manually
sudo -u zastava-agent docker ps
```

### Permission Denied Errors

```bash
# Add user to docker group (if not using ACLs)
sudo usermod -aG docker zastava-agent

# Restart agent
sudo systemctl restart zastava-agent
```

### Events Not Being Received

```bash
# Check Docker events stream
docker events --since 1m

# Verify agent can see events
journalctl -u zastava-agent | grep -i "event"

# Check event buffer
ls -la /var/lib/zastava-agent/runtime-events/
```

## References

- [Docker Engine Security](https://docs.docker.com/engine/security/)
- [Docker Socket Security](https://docs.docker.com/engine/security/protect-access/)
- [Rootless Docker](https://docs.docker.com/engine/security/rootless/)
- [docker-socket-proxy](https://github.com/Tecnativa/docker-socket-proxy)