For the past few days, memory usage was around 200MB. But when I checked the metrics, firecracker was (I think) using something like 190MB, and Grafana told me it was using only 60MB, so I thought this was strange.
Today, all of them has changed to around 60MB, and the firecracker graph tells me that it was always 60MB. What could have happened? The app seems to be running just fine.
Yes, good eye- we just deployed a change to the Overview page query to match the query already used in the Grafana dashboard.
The old query used
fly_instance_memory_mem_free, which only reported entirely free/unused memory, while the updated query (matching the one in the Grafana dashboard) uses
fly_instance_memory_mem_available, which reports ‘available’ memory, that doesn’t include memory used for filesystem cache/buffers that is nonetheless available for application use when needed. This gives a generally better approximation of memory usage for a simple overview.
Hope this explanation helps!