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SRV backend IPv6 support #222

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merged 3 commits into from
Jan 22, 2020
Merged

SRV backend IPv6 support #222

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99cb3df
IPv6 support for SRV discovery backend
erincandescent Jun 15, 2019
88599e6
Retain continue when no IP found
erincandescent Jun 15, 2019
f8392d0
Wrap IPv6s in square brackets for net.Dial
erincandescent Jun 15, 2019
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68 changes: 44 additions & 24 deletions src/discovery/srv.go
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Original file line number Diff line number Diff line change
Expand Up @@ -57,52 +57,50 @@ func srvFetch(cfg config.DiscoveryConfig) (*[]core.Backend, error) {
return &[]core.Backend{}, nil
}

/* ----- try to get A data from additional section ------ */
/* ----- try to get IPs from additional section ------ */

hosts := make(map[string]string) // name -> host
for _, ans := range r.Extra {
record, ok := ans.(*dns.A)
if !ok {
continue
switch record := ans.(type) {
case *dns.A:
hosts[record.Header().Name] = record.A.String()
case *dns.AAAA:
hosts[record.Header().Name] = fmt.Sprintf("[%s]", record.AAAA.String())
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This is slightly annoying - Gobetween uses net.Dial("tcp", addr) which requires bracketed IPv6s. If storing IPs here, it would be better to store them as net.IPs.

}

hosts[record.Header().Name] = record.A.String()
}

/* ----- create backends list looking up for A if needed ----- */
/* ----- create backend list looking up IP if needed ----- */

backends := []core.Backend{}
for _, ans := range r.Answer {

record, ok := ans.(*dns.SRV)
if !ok {
return nil, errors.New("Non-SRV record in SRV answer")
}

// If there were no A record in additional SRV response,
// Fetch it explicitelly
// If there were no A/AAAA record in additional SRV response,
// fetch it
if _, ok := hosts[record.Target]; !ok {
log.Debug("Fetching ", cfg.SrvLookupServer, " A/AAAA ", record.Target)

log.Debug("Fetching ", cfg.SrvLookupServer, " A ", record.Target)

resp, err := srvDnsLookup(cfg, record.Target, dns.TypeA)
ip, err := srvIPLookup(cfg, record.Target, dns.TypeA)
if err != nil {
log.Warn("Error fetching A record for ", record.Target, " skipping...")
continue
log.Warn("Error fetching A record for ", record.Target, ": ", err)
}

if len(resp.Answer) == 0 {
log.Warn("Empty answer for A records ", record.Target, " skipping...")
continue
if ip == "" {
ip, err = srvIPLookup(cfg, record.Target, dns.TypeAAAA)
if err != nil {
log.Warn("Error fetching AAAA record for ", record.Target, ": ", err)
}
}

a, ok := resp.Answer[0].(*dns.A)
if !ok {
log.Warn("Non-A record in A answer ", record.Target, " skipping...")
if ip != "" {
hosts[record.Target] = ip
} else {
log.Warn("No IP found for ", record.Target, ", skipping...")
continue
}

hosts[record.Target] = a.A.String()
}

// Append new backends
Expand All @@ -127,7 +125,6 @@ func srvFetch(cfg config.DiscoveryConfig) (*[]core.Backend, error) {
* Perform DNS Lookup with needed pattern and type
*/
func srvDnsLookup(cfg config.DiscoveryConfig, pattern string, typ uint16) (*dns.Msg, error) {

timeout := utils.ParseDurationOrDefault(cfg.Timeout, srvDefaultWaitTimeout)
c := dns.Client{Net: cfg.SrvDnsProtocol, Timeout: timeout}
m := dns.Msg{}
Expand All @@ -138,3 +135,26 @@ func srvDnsLookup(cfg config.DiscoveryConfig, pattern string, typ uint16) (*dns.

return r, err
}

/**
* Perform DNS lookup and extract IP address
*/
func srvIPLookup(cfg config.DiscoveryConfig, pattern string, typ uint16) (string, error) {
resp, err := srvDnsLookup(cfg, pattern, typ)
if err != nil {
return "", err
}

if len(resp.Answer) == 0 {
return "", nil
}

switch ans := resp.Answer[0].(type) {
case *dns.A:
return ans.A.String(), nil
case *dns.AAAA:
return fmt.Sprintf("[%s]", ans.AAAA.String()), nil
default:
return "", nil
}
}