collectd-libpod-stats

Collectd plugin for gathering resource usage statistics from containers created with the libpod library.

Functionality

This plugin is being developed with the new go-collectd library which has not yet released version 1. As a result, the functionality of this project is bound by the ever changing abilities of the library. Many features that would be expected from a plugin cannot yet be implemented until the library makes it possible to do so.

Right now, this plugin reports the following for each container on a node:

Resource	Units
cpu time	nS
cpu usage	percentage
memory usage	bytes

There is no way to configure these options.

Notes on memory usage calculations

Calculating memory usage on linux systems is hairy; not all projects do it the same way. This plugin replicates the memory calculation that the podman tool provides, using the value of memory.usage_in_bytes for cgroups v1 or memory.current for cgroups v2. This value includes both RSS and CACHE memory and is different to the value returned by the free tool, which calculates used memory by reading /proc/meminfo.

Kubernetes calulates the memory usage as memory.usage_in_bytes - total_inactive_file (source). K8s uses the value to make eviction decisions. Because k8s provides its own meanss of monitoring pod memory and calculates usage differently than this plugin and the free tool, this plugin should not be used to monitor pods in a k8s cluster.

Ultimately, the stated values are used here because the linux cgroup oom_killer uses this value to destroy processes that exceed the hard limit.

Build from source

Collectd library files must be made available to the golang compiler to build this plugin. Clone the collectd project. Then, run the following:

export COLLECTD_SRC="/path/to/collectd/source"
export CGO_CPPFLAGS="-I${COLLECTD_SRC}/src/daemon -I${COLLECTD_SRC}/src"


git clone https://github.com/infrawatch/collectd-libpod-stats.git
cd collectd-libpod-stats/plugin
go build -buildmode=c-shared -o libpodstats.so

collectd.conf

TypesDB "/path/to/types.db.libpodstats"

LoadPlugin "libpodstats"
<Plugin "libpodstats">
</Plugin>