Learning CoreDNS

Chapter 8. Monitoring and Troubleshooting

Given how critical a service DNS is, it’s important to have the ability to monitor its availability and performance and to troubleshoot problems it might be experiencing. In this chapter, we cover plug-ins that will help you monitor CoreDNS, log queries and responses, and diagnose issues.

The prometheus Plug-in

CoreDNS exposes many metrics using the prometheus plug-in. As the name suggests, these are exposed in the format used by the Prometheus monitoring system. The plug-in will open a port for Prometheus or other tools to scrape the metrics periodically.

Example 8-1 presents the complete syntax.

Example 8-1. Syntax of the prometheus plug-in

prometheus [ ADDRESS ]

ADDRESS is the IP and port to listen on; if omitted it defaults to localhost:9153.

The plug-in will start up an HTTP server with a handler for /metrics—any other path will result in an HTTP 404 Not Found error. CoreDNS will export basic process and Go runtime metrics as well as CoreDNS-specific metrics, as described in  Table 8-1.

Table 8-1. Exported metrics

Name	Labels	Description
process_cpu_seconds_total		Total user and system CPU time spent in seconds
process_open_fds		Number of open file descriptors
process_max_fds		Maximum number of open file descriptors
process_virtual_memory_bytes		Virtual memory size in bytes
process_virtual_memory_max_bytes		Maximum amount of virtual memory available in bytes
process_resident_memory_bytes		Resident memory ...