-
Notifications
You must be signed in to change notification settings - Fork 2.1k
Commit
This commit does not belong to any branch on this repository, and may belong to a fork outside of the repository.
dns: Added miekgdns resolver as a hidden option to query and ruler.
Fixes: #1015 Signed-off-by: Bartek Plotka <[email protected]>
- Loading branch information
Showing
11 changed files
with
287 additions
and
37 deletions.
There are no files selected for viewing
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,149 @@ | ||
| package miekgdns | ||
|
|
||
| import ( | ||
| "bytes" | ||
| "net" | ||
|
|
||
| "github.com/miekg/dns" | ||
| "github.com/pkg/errors" | ||
| ) | ||
|
|
||
| // Copied and slightly adjusted from Prometheus DNS SD: | ||
| // https://github.com/prometheus/prometheus/blob/be3c082539d85908ce03b6d280f83343e7c930eb/discovery/dns/dns.go#L212 | ||
|
|
||
| // lookupWithSearchPath tries to get an answer for various permutations of | ||
| // the given name, appending the system-configured search path as necessary. | ||
| // | ||
| // There are three possible outcomes: | ||
| // | ||
| // 1. One of the permutations of the given name is recognized as | ||
| // "valid" by the DNS, in which case we consider ourselves "done" | ||
| // and that answer is returned. Note that, due to the way the DNS | ||
| // handles "name has resource records, but none of the specified type", | ||
| // the answer received may have an empty set of results. | ||
| // | ||
| // 2. All of the permutations of the given name are responded to by one of | ||
| // the servers in the "nameservers" list with the answer "that name does | ||
| // not exist" (NXDOMAIN). In that case, it can be considered | ||
| // pseudo-authoritative that there are no records for that name. | ||
| // | ||
| // 3. One or more of the names was responded to by all servers with some | ||
| // sort of error indication. In that case, we can't know if, in fact, | ||
| // there are records for the name or not, so whatever state the | ||
| // configuration is in, we should keep it that way until we know for | ||
| // sure (by, presumably, all the names getting answers in the future). | ||
| // | ||
| // Outcomes 1 and 2 are indicated by a valid response message (possibly an | ||
| // empty one) and no error. Outcome 3 is indicated by an error return. The | ||
| // error will be generic-looking, because trying to return all the errors | ||
| // returned by the combination of all name permutations and servers is a | ||
| // nightmare. | ||
| func (r *Resolver) lookupWithSearchPath(name string, qtype dns.Type) (*dns.Msg, error) { | ||
| conf, err := dns.ClientConfigFromFile(r.ResolvConf) | ||
| if err != nil { | ||
| return nil, errors.Wrapf(err, "could not load resolv.conf: %s", err) | ||
| } | ||
|
|
||
| var errs []error | ||
| for _, lname := range conf.NameList(name) { | ||
| response, err := lookupFromAnyServer(lname, qtype, conf) | ||
| if err != nil { | ||
| // We can't go home yet, because a later name | ||
| // may give us a valid, successful answer. However | ||
| // we can no longer say "this name definitely doesn't | ||
| // exist", because we did not get that answer for | ||
| // at least one name. | ||
| errs = append(errs, err) | ||
| continue | ||
| } | ||
|
|
||
| if response.Rcode == dns.RcodeSuccess { | ||
| // Outcome 1: GOLD! | ||
| return response, nil | ||
| } | ||
| } | ||
|
|
||
| if len(errs) == 0 { | ||
| // Outcome 2: everyone says NXDOMAIN. | ||
| return &dns.Msg{}, nil | ||
| } | ||
| // Outcome 3: boned. | ||
| return nil, errors.Errorf("could not resolve %q: all servers responded with errors to at least one search domain. Errs %s", name, fmtErrs(errs)) | ||
| } | ||
|
|
||
| // lookupFromAnyServer uses all configured servers to try and resolve a specific | ||
| // name. If a viable answer is received from a server, then it is | ||
| // immediately returned, otherwise the other servers in the config are | ||
| // tried, and if none of them return a viable answer, an error is returned. | ||
| // | ||
| // A "viable answer" is one which indicates either: | ||
| // | ||
| // 1. "yes, I know that name, and here are its records of the requested type" | ||
| // (RCODE==SUCCESS, ANCOUNT > 0); | ||
| // 2. "yes, I know that name, but it has no records of the requested type" | ||
| // (RCODE==SUCCESS, ANCOUNT==0); or | ||
| // 3. "I know that name doesn't exist" (RCODE==NXDOMAIN). | ||
| // | ||
| // A non-viable answer is "anything else", which encompasses both various | ||
| // system-level problems (like network timeouts) and also | ||
| // valid-but-unexpected DNS responses (SERVFAIL, REFUSED, etc). | ||
| func lookupFromAnyServer(name string, qtype dns.Type, conf *dns.ClientConfig) (*dns.Msg, error) { | ||
| client := &dns.Client{} | ||
|
|
||
| var errs []error | ||
|
|
||
| // TODO(bwplotka): Worth to do fanout and grab fastest as golang native lib? | ||
| for _, server := range conf.Servers { | ||
| servAddr := net.JoinHostPort(server, conf.Port) | ||
| msg, err := askServerForName(name, qtype, client, servAddr, true) | ||
| if err != nil { | ||
| errs = append(errs, errors.Wrapf(err, "resolution against server %s for %s", server, name)) | ||
| continue | ||
| } | ||
|
|
||
| if msg.Rcode == dns.RcodeSuccess || msg.Rcode == dns.RcodeNameError { | ||
| return msg, nil | ||
| } | ||
| } | ||
|
|
||
| return nil, errors.Errorf("could not resolve %s: no servers returned a viable answer. Errs %v", name, fmtErrs(errs)) | ||
| } | ||
|
|
||
| func fmtErrs(errs []error) string { | ||
| b := bytes.Buffer{} | ||
| for _, err := range errs { | ||
| b.WriteString(";") | ||
| b.WriteString(err.Error()) | ||
| } | ||
| return b.String() | ||
| } | ||
|
|
||
| // askServerForName makes a request to a specific DNS server for a specific | ||
| // name (and qtype). Retries with TCP in the event of response truncation, | ||
| // but otherwise just sends back whatever the server gave, whether that be a | ||
| // valid-looking response, or an error. | ||
| func askServerForName(name string, qType dns.Type, client *dns.Client, servAddr string, edns bool) (*dns.Msg, error) { | ||
| msg := &dns.Msg{} | ||
|
|
||
| msg.SetQuestion(dns.Fqdn(name), uint16(qType)) | ||
| if edns { | ||
| msg.SetEdns0(dns.DefaultMsgSize, false) | ||
| } | ||
|
|
||
| response, _, err := client.Exchange(msg, servAddr) | ||
| if err != nil { | ||
| return nil, errors.Wrapf(err, "exchange") | ||
| } | ||
|
|
||
| if response.Truncated { | ||
| if client.Net == "tcp" { | ||
| return nil, errors.Errorf("got truncated message on TCP (64kiB limit exceeded?)") | ||
| } | ||
|
|
||
| // TCP fallback. | ||
| client.Net = "tcp" | ||
| return askServerForName(name, qType, client, servAddr, false) | ||
| } | ||
|
|
||
| return response, nil | ||
| } |
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,71 @@ | ||
| package miekgdns | ||
|
|
||
| import ( | ||
| "context" | ||
| "net" | ||
|
|
||
| "github.com/miekg/dns" | ||
| "github.com/pkg/errors" | ||
| ) | ||
|
|
||
| // DefaultResolvConfPath is a common, default resolv.conf file present on linux server. | ||
| const DefaultResolvConfPath = "/etc/resolv.conf" | ||
|
|
||
| // Resolver is a drop-in Resolver for *part* of std lib Golang net.DefaultResolver methods. | ||
| type Resolver struct { | ||
| ResolvConf string | ||
| } | ||
|
|
||
| func (r *Resolver) LookupSRV(ctx context.Context, service, proto, name string) (cname string, addrs []*net.SRV, err error) { | ||
| var target string | ||
| if service == "" && proto == "" { | ||
| target = name | ||
| } else { | ||
| target = "_" + service + "._" + proto + "." + name | ||
| } | ||
|
|
||
| response, err := r.lookupWithSearchPath(target, dns.Type(dns.TypeSRV)) | ||
| if err != nil { | ||
| return "", nil, err | ||
| } | ||
|
|
||
| for _, record := range response.Answer { | ||
| switch addr := record.(type) { | ||
| case *dns.SRV: | ||
| addrs = append(addrs, &net.SRV{ | ||
| Weight: addr.Weight, | ||
| Target: addr.Target, | ||
| Priority: addr.Priority, | ||
| Port: addr.Port, | ||
| }) | ||
| default: | ||
| return "", nil, errors.Errorf("invalid SRV response record %s", record) | ||
| } | ||
| } | ||
|
|
||
| return "", addrs, nil | ||
| } | ||
|
|
||
| func (r *Resolver) LookupIPAddr(ctx context.Context, host string) ([]net.IPAddr, error) { | ||
| response, err := r.lookupWithSearchPath(host, dns.Type(dns.TypeAAAA)) | ||
| if err != nil || len(response.Answer) == 0 { | ||
| // Ugly fallback to A lookup. | ||
| response, err = r.lookupWithSearchPath(host, dns.Type(dns.TypeA)) | ||
| if err != nil { | ||
| return nil, err | ||
| } | ||
| } | ||
|
|
||
| var resp []net.IPAddr | ||
| for _, record := range response.Answer { | ||
| switch addr := record.(type) { | ||
| case *dns.A: | ||
| resp = append(resp, net.IPAddr{IP: addr.A}) | ||
| case *dns.AAAA: | ||
| resp = append(resp, net.IPAddr{IP: addr.AAAA}) | ||
| default: | ||
| return nil, errors.Errorf("invalid A or AAAA response record %s", record) | ||
| } | ||
| } | ||
| return resp, nil | ||
| } |
Oops, something went wrong.