health

README

health

Name

health - enables a health check endpoint.

Description

Enabled process wide health endpoint. When CoreDNS is up and running this returns a 200 OK HTTP status code. The health is exported, by default, on port 8080/health.

Syntax

health [ADDRESS]

Optionally takes an address; the default is :8080. The health path is fixed to /health. The health endpoint returns a 200 response code and the word "OK" when this server is healthy.

An extra option can be set with this extended syntax:

health [ADDRESS] {
    lameduck DURATION
}

• Where lameduck will delay shutdown for DURATION. /health will still answer 200 OK. Note: The ready plugin will not answer OK while CoreDNS is in lame duck mode prior to shutdown.

If you have multiple Server Blocks, health can only be enabled in one of them (as it is process wide). If you really need multiple endpoints, you must run health endpoints on different ports:

com {
    whoami
    health :8080
}

net {
    erratic
    health :8081
}

Doing this is supported but both endpoints ":8080" and ":8081" will export the exact same health.

Metrics

If monitoring is enabled (via the prometheus plugin) then the following metrics are exported:

• coredns_health_request_duration_seconds{} - The health plugin performs a self health check once per second on the /health endpoint. This metric is the duration to process that request. As this is a local operation it should be fast. A (large) increase in this duration indicates the CoreDNS process is having trouble keeping up with its query load.
• coredns_health_request_failures_total{} - The number of times the self health check failed.

Note that these metrics do not have a server label, because being overloaded is a symptom of the running process, not a specific server.

Examples

Run another health endpoint on http://localhost:8091.

. {
    health localhost:8091
}

Set a lame duck duration of 1 second:

. {
    health localhost:8092 {
        lameduck 1s
    }
}

Documentation

Overview

Package health implements an HTTP handler that responds to health checks.

Index

• Variables

Variables

var (
	// HealthDuration is the metric used for exporting how fast we can retrieve the /health endpoint.
	HealthDuration = promauto.NewHistogram(prometheus.HistogramOpts{
		Namespace: plugin.Namespace,
		Subsystem: "health",
		Name:      "request_duration_seconds",
		Buckets:   plugin.SlimTimeBuckets,
		Help:      "Histogram of the time (in seconds) each request took.",
	})
	// HealthFailures is the metric used to count how many times the health request failed
	HealthFailures = promauto.NewCounter(prometheus.CounterOpts{
		Namespace: plugin.Namespace,
		Subsystem: "health",
		Name:      "request_failures_total",
		Help:      "The number of times the health check failed.",
	})
)