Using metering for compute resources

You can collect usage data of compute resources using Gnocchi. This time series database processes and stores measurement data of compute resources and provides access to it via REST API or the command-line tool.

Measurements can be sampled from such compute resources as virtual machines, VM disks and interfaces, compute networks, volumes, etc. All resources are being revised: if any attribute of a resource changes, this change is recorded in the history of the resource. For a VM, for example, you can measure the amount of allocated memory and virtual CPUs, as well as the memory and CPU usage.

An entity storing aggregates composed of a timestamp and value is called a metric. A metric is attached to a specific resource and associated to an archive policy. A policy defines how long aggregates are kept in a metric and how they are computed (minimum, maximum, average, etc.).

Two default archive policies, low and ceilometer-low-rate, are used for storing metrics. These policies imply that all computed aggregates are kept for one month with 5-minute granularity. The differences between them are the following:

  • ceilometer-low-rate is used for cumulative metrics and stores only mean values and the average of delta values per interval
  • low is used for gauge metrics and stores minimum, maximum, and mean values, standard deviation, as well as the sum and number of all measurements

The following metrics are available for aggregation:

Metric Type Resource type Description
memory gauge instance Amount of RAM allocated to the VM, in megabytes
memory.usage gauge instance Percentage of RAM used by the VM
vcpus gauge instance Number of virtual CPUs allocated to the VM
cpu cumulative instance Amount of CPU time used by the VM, in nanoseconds
disk.device.read.requests cumulative instance_disk Number of read requests
disk.device.write.requests cumulative instance_disk Number of write requests
disk.device.read.bytes cumulative instance_disk Amount of data read, in bytes
disk.device.write.bytes cumulative instance_disk Amount of data written, in bytes
network.incoming.bytes cumulative instance_network_interface Incoming network traffic, in bytes
network.outgoing.bytes cumulative instance_network_interface Outgoing network traffic, in bytes
network.incoming.packets cumulative instance_network_interface Incoming network traffic, in packets
network.outgoing.packets cumulative instance_network_interface Outgoing network traffic, in packets
image.size gauge image Size of the uploaded image, in bytes
volume.size gauge volume Size of the volume, in gigabytes
snapshot.size gauge volume Size of the volume snapshot, in gigabytes
magnum.cluster gauge coe_cluster Number of Container Orchestration Engine (COE), that is, Kubernetes clusters
bandwidth delta network Incoming and outgoing network traffic for a physical compute network, in bytes

Cumulative metrics are polled every 5 minutes and increase over time, delta metrics are polled every 5 minutes and change over time, and gauge metrics are updated on events and show fluctuating values.

Prerequisites