srv.go

Documentation: go.etcd.io/etcd/client/pkg/v3/srv

     1  // Copyright 2015 The etcd Authors
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  // Package srv looks up DNS SRV records.
    16  package srv
    17  
    18  import (
    19  	"fmt"
    20  	"net"
    21  	"net/url"
    22  	"strings"
    23  
    24  	"go.etcd.io/etcd/client/pkg/v3/types"
    25  )
    26  
    27  var (
    28  	// indirection for testing
    29  	lookupSRV      = net.LookupSRV // net.DefaultResolver.LookupSRV when ctxs don't conflict
    30  	resolveTCPAddr = net.ResolveTCPAddr
    31  )
    32  
    33  // GetCluster gets the cluster information via DNS discovery.
    34  // Also sees each entry as a separate instance.
    35  func GetCluster(serviceScheme, service, name, dns string, apurls types.URLs) ([]string, error) {
    36  	tempName := int(0)
    37  	tcp2ap := make(map[string]url.URL)
    38  
    39  	// First, resolve the apurls
    40  	for _, url := range apurls {
    41  		tcpAddr, err := resolveTCPAddr("tcp", url.Host)
    42  		if err != nil {
    43  			return nil, err
    44  		}
    45  		tcp2ap[tcpAddr.String()] = url
    46  	}
    47  
    48  	stringParts := []string{}
    49  	updateNodeMap := func(service, scheme string) error {
    50  		_, addrs, err := lookupSRV(service, "tcp", dns)
    51  		if err != nil {
    52  			return err
    53  		}
    54  		for _, srv := range addrs {
    55  			port := fmt.Sprintf("%d", srv.Port)
    56  			host := net.JoinHostPort(srv.Target, port)
    57  			tcpAddr, terr := resolveTCPAddr("tcp", host)
    58  			if terr != nil {
    59  				err = terr
    60  				continue
    61  			}
    62  			n := ""
    63  			url, ok := tcp2ap[tcpAddr.String()]
    64  			if ok {
    65  				n = name
    66  			}
    67  			if n == "" {
    68  				n = fmt.Sprintf("%d", tempName)
    69  				tempName++
    70  			}
    71  			// SRV records have a trailing dot but URL shouldn't.
    72  			shortHost := strings.TrimSuffix(srv.Target, ".")
    73  			urlHost := net.JoinHostPort(shortHost, port)
    74  			if ok && url.Scheme != scheme {
    75  				err = fmt.Errorf("bootstrap at %s from DNS for %s has scheme mismatch with expected peer %s", scheme+"://"+urlHost, service, url.String())
    76  			} else {
    77  				stringParts = append(stringParts, fmt.Sprintf("%s=%s://%s", n, scheme, urlHost))
    78  			}
    79  		}
    80  		if len(stringParts) == 0 {
    81  			return err
    82  		}
    83  		return nil
    84  	}
    85  
    86  	err := updateNodeMap(service, serviceScheme)
    87  	if err != nil {
    88  		return nil, fmt.Errorf("error querying DNS SRV records for _%s %s", service, err)
    89  	}
    90  	return stringParts, nil
    91  }
    92  
    93  type SRVClients struct {
    94  	Endpoints []string
    95  	SRVs      []*net.SRV
    96  }
    97  
    98  // GetClient looks up the client endpoints for a service and domain.
    99  func GetClient(service, domain string, serviceName string) (*SRVClients, error) {
   100  	var urls []*url.URL
   101  	var srvs []*net.SRV
   102  
   103  	updateURLs := func(service, scheme string) error {
   104  		_, addrs, err := lookupSRV(service, "tcp", domain)
   105  		if err != nil {
   106  			return err
   107  		}
   108  		for _, srv := range addrs {
   109  			urls = append(urls, &url.URL{
   110  				Scheme: scheme,
   111  				Host:   net.JoinHostPort(srv.Target, fmt.Sprintf("%d", srv.Port)),
   112  			})
   113  		}
   114  		srvs = append(srvs, addrs...)
   115  		return nil
   116  	}
   117  
   118  	errHTTPS := updateURLs(GetSRVService(service, serviceName, "https"), "https")
   119  	errHTTP := updateURLs(GetSRVService(service, serviceName, "http"), "http")
   120  
   121  	if errHTTPS != nil && errHTTP != nil {
   122  		return nil, fmt.Errorf("dns lookup errors: %s and %s", errHTTPS, errHTTP)
   123  	}
   124  
   125  	endpoints := make([]string, len(urls))
   126  	for i := range urls {
   127  		endpoints[i] = urls[i].String()
   128  	}
   129  	return &SRVClients{Endpoints: endpoints, SRVs: srvs}, nil
   130  }
   131  
   132  // GetSRVService generates a SRV service including an optional suffix.
   133  func GetSRVService(service, serviceName string, scheme string) (SRVService string) {
   134  	if scheme == "https" {
   135  		service = fmt.Sprintf("%s-ssl", service)
   136  	}
   137  
   138  	if serviceName != "" {
   139  		return fmt.Sprintf("%s-%s", service, serviceName)
   140  	}
   141  	return service
   142  }
   143
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