Good Free VPS Server Monitoring
Does anyone have any recommendations for a decent free monitoring tool for Linux (specifically Ubuntu 14.04)?
Needs to handle metrics (so CPU, RAM, network) and (ideally) email-based alerting for < 5 servers, and be SaaS. Retention isn't a huge issue but 1 month would be nice.
Ideally something like StackDriver or NewRelic would do, but I'm unsure exactly how many servers NR's Lite tier supports, or whether you can just monitor servers on their own without app-level reporting.