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dnschecker.go
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dnschecker.go
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package checkup
import (
"fmt"
"net"
"time"
"github.com/miekg/dns"
)
// DNSChecker implements a Checker for TCP endpoints.
type DNSChecker struct {
// Name is the name of the endpoint.
Name string `json:"endpoint_name"`
// This is the name of the DNS server you are testing.
URL string `json:"endpoint_url"`
// This is the fqdn of the target server to query the DNS server for.
Host string `json:"hostname_fqdn,omitempty"`
// Timeout is the maximum time to wait for a
// TCP connection to be established.
Timeout time.Duration `json:"timeout,omitempty"`
// ThresholdRTT is the maximum round trip time to
// allow for a healthy endpoint. If non-zero and a
// request takes longer than ThresholdRTT, the
// endpoint will be considered unhealthy. Note that
// this duration includes any in-between network
// latency.
ThresholdRTT time.Duration `json:"threshold_rtt,omitempty"`
// Attempts is how many requests the client will
// make to the endpoint in a single check.
Attempts int `json:"attempts,omitempty"`
}
// Check performs checks using c according to its configuration.
// An error is only returned if there is a configuration error.
func (c DNSChecker) Check() (Result, error) {
if c.Attempts < 1 {
c.Attempts = 1
}
result := Result{Title: c.Name, Endpoint: c.URL, Timestamp: Timestamp()}
result.Times = c.doChecks()
return c.conclude(result), nil
}
// doChecks executes and returns each attempt.
func (c DNSChecker) doChecks() Attempts {
var err error
var conn net.Conn
timeout := c.Timeout
if timeout == 0 {
timeout = 1 * time.Second
}
checks := make(Attempts, c.Attempts)
for i := 0; i < c.Attempts; i++ {
start := time.Now()
if c.Host != "" {
hostname := c.Host
m1 := new(dns.Msg)
m1.Id = dns.Id()
m1.RecursionDesired = true
m1.Question = make([]dns.Question, 1)
m1.Question[0] = dns.Question{Name: hostname, Qtype: dns.TypeA, Qclass: dns.ClassINET}
d := new(dns.Client)
if err != nil {
checks[i].Error = err.Error()
continue
}
_, _, err := d.Exchange(m1, c.URL)
if err != nil {
checks[i].Error = err.Error()
continue
}
}
if conn, err = net.DialTimeout("tcp", c.URL, c.Timeout); err == nil {
conn.Close()
}
checks[i].RTT = time.Since(start)
if err != nil {
checks[i].Error = err.Error()
continue
}
}
return checks
}
// conclude takes the data in result from the attempts and
// computes remaining values needed to fill out the result.
// It detects degraded (high-latency) responses and makes
// the conclusion about the result's status.
func (c DNSChecker) conclude(result Result) Result {
result.ThresholdRTT = c.ThresholdRTT
// Check errors (down)
for i := range result.Times {
if result.Times[i].Error != "" {
result.Down = true
return result
}
}
// Check round trip time (degraded)
if c.ThresholdRTT > 0 {
stats := result.ComputeStats()
if stats.Median > c.ThresholdRTT {
result.Notice = fmt.Sprintf("median round trip time exceeded threshold (%s)", c.ThresholdRTT)
result.Degraded = true
return result
}
}
result.Healthy = true
return result
}