I am still not clear about Stackdriver Logging & Monitoring Agents. What are the major differences between these two ? It aso says that they are not mandatory then how do we get telemetry/logs from VM instances ?
Stackdriver Monitoring gathers metrics from VMs in your infrastructure. Things like CPU usage, process metrics etc. Things like this helps you understand whats going on and how to troubleshoot if you find any issues.
So more like a watch dog that will tell you when something is wrong immediatly.
Stackdriver give you access to log and store your logging data withing Google Cloud. With this, you are able to query data to look at, and get granular to whats going on in your infrastructure! So more like records that you can keep in your back in to look at later if I make sense.