Prometheus: Prometheus is a popular open-source monitoring and alerting system that is highly recommended for monitoring GitLab on Ubuntu. It can collect metrics from various sources, including GitLab, and provide powerful querying and alerting capabilities.

Grafana: Grafana is a visualization tool that works well with Prometheus and other monitoring systems. It allows you to create dashboards and graphs to visualize the metrics collected by Prometheus, making it easier to monitor the performance and health of your GitLab instance on Ubuntu.

Netdata: Netdata is a real-time performance monitoring tool that is lightweight and easy to install on Ubuntu. It provides detailed insights into system and application performance, including metrics related to CPU, memory, disk, and network usage. Netdata can be used to monitor GitLab’s resource consumption and identify any performance issues.

Zabbix: Zabbix is a comprehensive monitoring solution that can be used to monitor various aspects of your GitLab instance on Ubuntu, such as server availability, performance metrics, and system health. It offers a wide range of monitoring capabilities and supports alerts, notifications, and reporting features.

Nagios: Nagios is a popular open-source monitoring tool that is widely used for monitoring servers, services, and applications. It can be configured to monitor GitLab on Ubuntu and alert you to any issues or anomalies in real-time. Nagios offers a flexible and extensible monitoring framework that can be customized to meet your specific monitoring requirements.