prometheus/retrieval/target_provider.go

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// Copyright 2013 The Prometheus Authors
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package retrieval
import (
"fmt"
"net"
"net/url"
"strings"
"time"
"github.com/golang/glog"
"github.com/miekg/dns"
"github.com/prometheus/client_golang/prometheus"
clientmodel "github.com/prometheus/client_golang/model"
"github.com/prometheus/prometheus/config"
"github.com/prometheus/prometheus/utility"
)
const resolvConf = "/etc/resolv.conf"
var (
dnsSDLookupsCount = prometheus.NewCounter(
prometheus.CounterOpts{
Namespace: namespace,
Name: "dns_sd_lookups_total",
Help: "The number of DNS-SD lookups.",
})
dnsSDLookupFailuresCount = prometheus.NewCounter(
prometheus.CounterOpts{
Namespace: namespace,
Name: "dns_sd_lookup_failures_total",
Help: "The number of DNS-SD lookup failures.",
})
)
func init() {
prometheus.MustRegister(dnsSDLookupFailuresCount)
prometheus.MustRegister(dnsSDLookupsCount)
}
// TargetProvider encapsulates retrieving all targets for a job.
type TargetProvider interface {
// Retrieves the current list of targets for this provider.
Targets() ([]Target, error)
}
type sdTargetProvider struct {
job config.JobConfig
targets []Target
lastRefresh time.Time
refreshInterval time.Duration
}
// NewSdTargetProvider constructs a new sdTargetProvider for a job.
func NewSdTargetProvider(job config.JobConfig) *sdTargetProvider {
i, err := utility.StringToDuration(job.GetSdRefreshInterval())
if err != nil {
panic(fmt.Sprintf("illegal refresh duration string %s: %s", job.GetSdRefreshInterval(), err))
}
return &sdTargetProvider{
job: job,
refreshInterval: i,
}
}
func (p *sdTargetProvider) Targets() ([]Target, error) {
var err error
defer func() {
dnsSDLookupsCount.Inc()
if err != nil {
dnsSDLookupFailuresCount.Inc()
}
}()
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if time.Since(p.lastRefresh) < p.refreshInterval {
return p.targets, nil
}
response, err := lookupSRV(p.job.GetSdName())
if err != nil {
return nil, err
}
baseLabels := clientmodel.LabelSet{
clientmodel.JobLabel: clientmodel.LabelValue(p.job.GetName()),
}
targets := make([]Target, 0, len(response.Answer))
endpoint := &url.URL{
Scheme: "http",
Path: p.job.GetMetricsPath(),
}
for _, record := range response.Answer {
addr, ok := record.(*dns.SRV)
if !ok {
glog.Warningf("%s is not a valid SRV record", addr)
continue
}
// Remove the final dot from rooted DNS names to make them look more usual.
if addr.Target[len(addr.Target)-1] == '.' {
addr.Target = addr.Target[:len(addr.Target)-1]
}
endpoint.Host = fmt.Sprintf("%s:%d", addr.Target, addr.Port)
t := NewTarget(endpoint.String(), p.job.ScrapeTimeout(), baseLabels)
targets = append(targets, t)
}
p.targets = targets
return targets, nil
}
func lookupSRV(name string) (*dns.Msg, error) {
conf, err := dns.ClientConfigFromFile(resolvConf)
if err != nil {
return nil, fmt.Errorf("couldn't load resolv.conf: %s", err)
}
client := &dns.Client{}
response := &dns.Msg{}
for _, server := range conf.Servers {
servAddr := net.JoinHostPort(server, conf.Port)
for _, suffix := range conf.Search {
response, err = lookup(name, dns.TypeSRV, client, servAddr, suffix, false)
if err == nil {
if len(response.Answer) > 0 {
return response, nil
}
} else {
glog.Warningf("resolving %s.%s failed: %s", name, suffix, err)
}
}
response, err = lookup(name, dns.TypeSRV, client, servAddr, "", false)
if err == nil {
return response, nil
}
}
return response, fmt.Errorf("couldn't resolve %s: No server responded", name)
}
func lookup(name string, queryType uint16, client *dns.Client, servAddr string, suffix string, edns bool) (*dns.Msg, error) {
msg := &dns.Msg{}
lname := strings.Join([]string{name, suffix}, ".")
msg.SetQuestion(dns.Fqdn(lname), queryType)
if edns {
opt := &dns.OPT{
Hdr: dns.RR_Header{
Name: ".",
Rrtype: dns.TypeOPT,
},
}
opt.SetUDPSize(dns.DefaultMsgSize)
msg.Extra = append(msg.Extra, opt)
}
response, _, err := client.Exchange(msg, servAddr)
if err != nil {
return nil, err
}
if msg.Id != response.Id {
return nil, fmt.Errorf("DNS ID mismatch, request: %d, response: %d", msg.Id, response.Id)
}
if response.MsgHdr.Truncated {
if client.Net == "tcp" {
return nil, fmt.Errorf("got truncated message on tcp")
}
if edns { // Truncated even though EDNS is used
client.Net = "tcp"
}
return lookup(name, queryType, client, servAddr, suffix, !edns)
}
return response, nil
}