The dnscache-stats program can be used to send metrics generated from the log entries of the dnscache program to a graphite-compatible metrics database.

Usage

dnscache-stats [-i 60s] [-m metrics-template] [-f file] graphite-host[:port]

Dnscache-stats will read data on standard input, and upload various metrics to the provided server using Graphite's plain-text protocol format. If graphite-host is a file name (begins with '.' or '/'), metrics are appended to the file instead. All data read on stdin is echoed to stdout, unmodified, so that dnscache-stats can be used as a log script for dnscache:

#!/bin/bash
exec > >(exec setuidgid Gdnslog multilog t ./main)
exec setuidgid Gdnslog dnscache-stats graphite.example.net

This is the recommended way to run dnscache-stats. Alternatively, it can be run as a standalone service using the -f flag. Here is an example systemd unit file for such a service:

[Unit]
Description=send dnscache metrics to graphite

[Service]
ExecStart=/usr/bin/dnscache-stats -f /service/dnscache/log/main/current graphite.example.net
Restart=always

[Install]
WantedBy=multi-user.target

By default, dnscache-stats will generate one data point for each metric every minute. The interval between data points can be changed with the -i option. To change the interval to 5 minutes, run:

dnscache-stats -i 5m graphite.example.net

By default, metrics names will be of the form

servers.HOSTNAME.dnscache.METRIC_NAME

This naming convention is taken from Diamond. The -m flag can be used to change the naming convention. For instance, to change the naming convention to the collectd convention, run:

dnscache-stats -m 'collectd.{{.Hostname}}.dnscache.{{.Metric}}'

Within the template, .Service will be the name of the service directory used by daemontools, if it is possible to infer. For instance, if dnscache-stats is run from /service/dnscache-primary/log, then the command

dnscache-stats -m servers.{{.Hostname}}.dnscache.{{.Service|rstrip "dnscache-"}}.{{.Metric}}

will generate metrics such as the following

servers.myhost01.dnscache.primary.cache_motion

Metrics collected

dnscache-stats collects the following metrics. The following description assumes the default interval (-i option) of 1 minute:

• queries: number of queries received in the last minute
• cache_motion: number of bytes written to the cache in the last minute
• udp_active: max sample of the number of pending (unfinished) UDP queries over the last minute
• tcp_active: max sample of the number of pending (unfinished) TCP queries over the last minute
• cache_hits: number of cache hits
• drop: the number of dropped queries
• query_avg_us: mean query time of all requests in the last minute (μs)
• query_max_us: slowest query in the last minute (μs)
• servfail: number of failure responses sent
• tx: number of outgoing queries dnscache made to resolve a record

See this page for a helpful description of the information available in dnscache's log output.

Operational notes

• When measuring the query_avg and query_max metrics, dnscache-stats will only consider the first 100,000 queries. This is to prevent dnscache-stats from consuming an unpredictable amount of memory and is controlled by the compile-time constant QueryTrackingLimit.
• dnscache-stats will buffer up to 100 metrics in memory if they cannot be sent to the graphite server. Once the buffer is filled, the oldest metrics are dropped first. This is controlled by the compile-time constant MetricsBufferMax.
• dnscache-stats will exit if it can no longer write to stdout. This is important when running dnscache-stats as a log program under daemontools, as it will ensure that the supervise program will restart it if multilog dies.
• When following a physical file (via the -f flag), dnscache will attempt to detect and re-open the file if it is renamed (such as during log rotation). This process is imperfect and can result in (very small) errors in metrics.

Building and developing dnscache-stats

Dnscache-stats is written with Go, and can be built with Go version 1.6 or above. To build dnscache, run

go build

Or, to fetch, build and install dnscache-stats to $GOPATH/bin, run

go get github.com/droyo/dnscache-stats

Pull requests are welcome, and any issues can be opened through github. Please run go test and go fmt before submitting any changes.

Packaging and deploying dnscache-stats

The contrib directory contains an RPM spec file that can be used to package the dnscache-stats program. Pre-packaged RPMs and binary tarballs can be found under the github releases for this repository. Binary releases are built with the latest stable version of Go at the time of the release.