Monitoring in DevOps is the practice of collecting and analyzing data about the performance and stability of services and infrastructure to improve the system's reliability. Key aspects include:

1. **Infrastructure Monitoring:**
   - Server health
   - Network performance
   - Resource utilization

2. **Application Monitoring:**
   - Response times
   - Error rates
   - Request rates

3. **User Experience Monitoring:**
   - Page load times
   - User interactions
   - Conversion rates

ELK Stack is a collection of three open-source products:

1. **Elasticsearch:** A search and analytics engine
2. **Logstash:** A server‑side data processing pipeline
3. **Kibana:** A visualization tool for Elasticsearch data

Common use cases:
- Log aggregation
- Security analytics
- Application performance monitoring
- Website search
- Business analytics

Prometheus is an open-source systems monitoring and alerting toolkit. Key features include:

1. **Time series database**
2. **Flexible query language (PromQL)**
3. **Pull-based metrics collection**
4. **Alert management**
5. **Visualization capabilities**

Example of Prometheus configuration:
```yaml
global:
  scrape_interval: 15s

scrape_configs:
  - job_name: 'prometheus'
    static_configs:
      - targets: ['localhost:9090']

  - job_name: 'node'
    static_configs:
      - targets: ['localhost:9100']
```

Grafana is an open-source analytics and monitoring solution that allows you to query, visualize, and alert on your metrics no matter where they are stored. Key features include:

1. **Data source integration**
2. **Dashboard creation**
3. **Alerting**
4. **Visualization**
5. **User interface**

Monitoring and logging are two different practices in DevOps:

1. **Monitoring:**
   - Focuses on collecting and analyzing data about the performance and stability of services and infrastructure to improve the system's reliability.
   - Key aspects include:
     - Infrastructure Monitoring
     - Application Monitoring
     - User Experience Monitoring

2. **Logging:**
   - Focuses on collecting and analyzing log data to help diagnose and troubleshoot issues.
   - Key aspects include:
     - Log aggregation
     - Security analytics
     - Application performance monitoring
     - Website search
     - Business analytics