Sensu

Overview

Founded in 2011 and headquartered in Portland, Oregon, USA, Sensu is an open-source event-driven monitoring framework. Originally written in Ruby, the 2018 release of Sensu Go was a complete rewrite in Go, dramatically improving performance, deployment simplicity, and resource efficiency — a single node handles 10,000+ events per second with a 40MB binary and no Ruby runtime dependency.

Sensu's core architecture is based on the Pipeline mechanism: monitoring events collected by Agents flow through Filters → Handlers → Alert Routing, with each stage extensible via plugins. This design positions Sensu as a "monitoring event router" — unifying events from diverse sources, processing them, and routing them to alerting systems, ticketing platforms, time-series databases, or automation tools. The community maintains 300+ plugins covering infrastructure, applications, cloud services, and network devices.

Key Strengths

• Event-Driven Pipeline Architecture: Sensu's core is an event processing pipeline — Filters decide which events to process, Handlers determine how (alert/InfluxDB write/trigger automation), and routing decides where to send. Each stage is independently replaceable and composable for highly customizable monitoring workflows.
• Sensu Go High Performance: Go rewrite delivers 10,000+ events/sec per node with memory usage as low as 50MB. Static binary deployment with no Ruby/JVM dependency; single-node setup in under 5 minutes.
• Cloud Native & Container Friendly: Lightweight Agent (~20MB) deploys as a Sidecar in Kubernetes Pods. Auto-discovers K8s nodes and services, and works complementarily with Prometheus Operator.
• 300+ Plugin Ecosystem: Community-maintained plugins for Ping/HTTP/TCP checks, Docker/Kubernetes monitoring, Elasticsearch/MySQL/Redis health checks, and PagerDuty/Slack/Opsgenie alert integrations.

Product Ecosystem

• Sensu Agent: Lightweight agent installed on monitored targets, executes check scripts and sends results as events to the Backend. Supports auto-registration and de-registration.
• Sensu Backend: Core service receiving agent events, executing Pipeline processing, and maintaining state and asset management. Embedded BoltDB for single-node; optional Etcd for HA clustering.
• Pipeline: Event processing chain composed of Filters, Handlers, and Mutators. Filters can condition on severity, source, time window, etc. Handlers support multiple outputs (alerting, metric storage, Webhooks). Mutators format event data for specific targets.
• Assets: Sensu Go's resource management mechanism — plugins distributed as container images or archives, auto-downloaded and cached by Backend to Agents, eliminating per-machine manual installation.

Limitations

• Moderate to High Learning Curve: Pipeline concepts (Filter/Handler/Mutator/Asset) and configuration require dedicated learning time. Teams migrating from Prometheus or Nagios typically need 1-2 weeks to become proficient.
• Smaller Community: Compared to Prometheus (60,000+ GitHub Stars), Sensu's community is roughly 10x smaller. Fewer third-party integrations, blog tutorials, and Stack Overflow resources available.
• Weak Built-in Visualization: Sensu does not provide rich dashboard capabilities natively. Metric visualization requires Grafana, and the event dashboard is basic.
• Slower Open-Source Cadence: As parent company Catage focuses on Sensu Cloud commercialization, the open-source Sensu Go release frequency has decreased, increasing the need for community forks and custom plugins.

Use Cases

• Kubernetes / Container Environments (★★★★★): Sidecar Agent deployment with auto-discovery of Pods and services, event-driven alerting.
• Cloud Native Monitoring Pipeline (★★★★): Unify alert events from Prometheus, CloudWatch, and logging systems into PagerDuty/Slack.
• DevOps Automation Teams (★★★★): Teams needing flexible monitoring event processing and automated incident response.
• Self-Built Monitoring Stacks (★★★★): Use Sensu as the event routing core, paired with Prometheus (metrics) + Grafana (dashboards) for a complete monitoring platform.

Pricing

FAQ

• What is the difference between Sensu and Prometheus? Sensu is an event-driven monitoring framework focused on event processing and routing. Prometheus is a pull-based time-series monitoring system focused on metric collection and querying. They are complementary — Prometheus collects metrics, Sensu handles alert event routing. See Prometheus Monitoring Setup Guide.
• Does Sensu Go require a database? Sensu Go embeds BoltDB for single-node storage and uses Etcd for cluster mode. No external database deployment needed. See Cloud Monitoring Services Comparison.
• Does Sensu support alerting? Yes. Through the Pipeline Handler mechanism, events can be routed to PagerDuty, Slack, Opsgenie, Email, and custom Webhooks. See Alert Fatigue & On-Call Practice.
• How large is the feature gap between Sensu Go and Sensu Cloud? Sensu Go (community edition) is fully functional and self-sufficient. Sensu Cloud provides a managed Backend with auto-upgrades, ideal for teams that want to avoid self-hosting Sensu infrastructure. See Cloud Monitoring Services Comparison.