collectd
A daemon that collects system performance statistics periodically, and provides tons of plugins to store and analyze these values
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jmxtrans
Plugs Java VM statistics via JMX to various backend monitoring tools
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Logstash
A modern tool for managing events and logs, with an ElasticSearch backend which allows a high degree of searching and filtering. It includes a shipper in remote systems, indexer in the aggregator machine, and a Web UI.
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Metrics
Captures JVM and application-level metrics for Java
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Monit
An open source utility for managing and monitoring processes, programs, files, directories and filesystems
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Nagios Core
Nagios Core network monitoring software is a powerful, enterprise-class host, server, application, monitoring and alerting tool
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Prevoty Application Monitoring & Protection (AMP)
Prevoty enables DevOps to inject security into your web applications and web services. Protection is provided at runtime from within the application itself, and stays with the app regardless of deployment method (cloud, on-premises, etc). Applications are protected against threats including XSS, SQLi, CSRF, command injection, etc. Works with Puppet, Chef, Ansible, Docker, Splunk, QRadar, ELK, and many others.
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Sentry
Automate error tracking to find and fix issues before your users even experience a crash. Sentry is open-source, real-time, and loved by 100,000 developers around the world.
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testssl.sh
A command-line tool which checks a server's service on any port for the support of TLS/SSL ciphers, protocols as well as some cryptographic flaws. It's designed to provide clear output for your "is this good or bad" decision.
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Zabbix
An open source, enterprise-class monitoring framework
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