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Sensu is an open source service monitoring framework written in Ruby that uses check scripts to track servers, services, application health and business key performance indicators. Sensu allows users to collect metrics; offers a documented API to request check executions and resolve events; provides SSL encryption, authentication, and granular access control lists; and is packaged with a TCP and UDP socket that can accept external JSON data. With the ability to monitor more than 10,000 servers, Sensu can be used by small companies, large enterprises and everything in between.
Sensu's service monitoring framework uses three core components: the server, the client and the API. The Sensu server orchestrates check executions, processes the results and handles events. The Sensu client receives the check executions before completing them and publishing the results. Finally, the Sensu API provides a RESTful interface to data (such as registered clients and current events). It is capable of many actions, including issuing check execution requests, resolving events and removing registered clients. Currently, official support is limited to the operating systems Debian/Ubuntu and CentOS/RHEL; however, the client will run on any OS as long as Ruby is installed. Sensu plans to release official clients for a number of new platforms (Solaris, FreeBSD and others) in 2016.
The service monitoring framework from Sensu also collects metrics from server resources, services and applications, and allows for data output in a variety of formats including Graphite plaintext, Nagios Performance Data, OpenTSDB and Metric 2.0 wire formats. It integrates with a number of other tools and services, among them Flapjack, Librato Solar Winds, Chef and influxDB. Sensu's dashboard (based on Uchiwa) can run in multiple instances and be navigated by multiple users at a time. Sensu is a framework appropriate for any stage of the development process.
The latest version of the monitoring framework, 0.21 (client) and 1.10.0 (Enterprise Server), is available in two editions, Sensu Core and Sensu Enterprise. Sensu Core (the open source software project) provides an open framework for building comprehensive monitoring solutions, without imposing restrictions or being overly opinionated. Although new user-facing "features" may be developed exclusively in Sensu Enterprise, Sensu Core's framework that makes those features possible will never change.
Sensu Core is free and requires a generic MIT license. Sensu Enterprise offers a non-exclusive and unlimited license based on servers monitored beginning at $50 a month for 50 servers. A progressive volume discount is offered to users who operate 1,000 or more servers (up to 50% off); customers receive two months free when they pay annually.
Sensu Enterprise is a subscription service that offers features and support access that go beyond Sensu Core. It is packaged with an enhanced dashboard, native integrations, built-in contact routing and metric translation. A more robust support system gives subscribers access to the Sensu Enterprise Helpdesk, with a four-hour response time and next-business-day resolution for Level 1 issues. Premium Support is also available for $5,000 per month, including phone support, 24-hour coverage 365 days a year and faster response times. Sensu Enterprise provides the user with one free seat at their annual training events (normally $599 and upward per seat).
Sensu Enterprise allows for server count to fluctuate based on demand in order to remain flexible when dealing with dynamic infrastructures, asking that users pay only for those servers they have "at rest." It is sold directly from the vendor Heavy Water Operations and installed on premises. Sensu offers a free, 14-day trial for its service monitoring framework.
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