Cacti vs Nagios vs Sensu: What are the differences?

**Introduction:**

Key differences between Cacti, Nagios, and Sensu:

1. **Functionality**: Cacti is primarily a graphing solution for time-series data providing real-time graphs, while Nagios focuses on monitoring network services and components and alerting if any issues are detected. Sensu offers a more comprehensive monitoring solution with event handling, targeted at cloud-scale infrastructures and dynamic environments.

2. **Alerting Mechanism**: Nagios uses a traditional alerting mechanism where notifications are sent directly based on predefined thresholds. Cacti, on the other hand, lacks built-in alerting capabilities and requires integration with external tools for alerting. Sensu allows for more customizable alerting using its event handler infrastructure, enabling users to define complex alerting logic.

3. **Scalability**: Cacti is more suitable for smaller environments with simpler monitoring needs due to its limitations in scalability compared to Nagios and Sensu. Nagios can easily scale to monitor large and complex networks with distributed monitoring setups. Sensu is designed to be highly scalable, supporting auto-discovery and flexible deployment options for dynamic environments.

4. **Agent-based vs. Agentless**: Nagios and Sensu are agent-based monitoring solutions, where agents are deployed on each host to collect data and send it back to the central monitoring server. In contrast, Cacti is agentless and relies on SNMP (Simple Network Management Protocol) for data collection, making it easier to set up for some users but limiting the depth of data that can be gathered.

5. **Community and Support**: Nagios has a large and active community with extensive documentation and plugins available, making it easier to find solutions and integrations. Cacti also has a good community but may have fewer resources compared to Nagios. Sensu, being a newer solution, has a growing community but may have limited resources and integrations available compared to Nagios and Cacti.

6. **Cost**: Cacti and Nagios are open-source solutions, providing cost-effective monitoring options for businesses. Sensu, while offering an open-source version, has an enterprise version with additional features and support, which may incur costs for businesses looking for advanced functionalities and support services.

In Summary, the key differences between Cacti, Nagios, and Sensu lie in their core functionality, alerting mechanisms, scalability, monitoring approach, community support, and cost implications.