A simple DNS server that returns different answers depending on the IP address of the client making the request
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README.md

rancher-dns

Build Status

A simple DNS server that returns different answers depending on the IP address of the client making the request.

Usage

  rancher-dns [--debug] [--listen host:port] [--ttl num] [--log path] [--pid-file path]--answers /path/to/answers.(yaml|json)

Compile

  godep go build

CLI Options

Option Default Description
--debug off If present, more debug info is logged
--listen 0.0.0.0:53 IP address and port to listen on (TCP & UDP)
--answers ./answers.(yaml json)
--ttl 600 Default TTL for local responses that are returned
--ndots 0 (unlimited) Only recurse if there are less than this number of dots
--log none Output log info to a file path instead of stdout
--pid-file none Write the server PID to a file path on startup

JSON Answers File

{
  "10.1.2.2": {
    // DNS servers to recurse to when answers are not found locally
    "recurse": ["8.8.4.4:53", "8.8.8.8"],

    // Search suffixes to try to find a match inside the answers file.
    // For queries consisting of a single label, e.g. "mysql.", rancher-dns will
    // try appending these suffixes one a a time and looking for an answer
    // ("mysql.", "mysql.x.discover.internal", and "mysql.discover.internal")
    // before moving on to the "default" key or recursive lookup.
    "search": ["x.discover.internal","discover.internal"],

    // A records
    "a": {
      // FQDN => { answer: array of IPs, ttl: TTL for this specific answer }
      // Note: Key must be fully-qualified (ending in dot) and all lowercase
      "mysql.": {"answer": ["10.1.2.3"], "ttl": 42},
      "web.": {"answer": ["10.1.2.4","10.1.2.5","10.1.2.6"]}
    },

    // CNAME records
    "cname": {
      // FQDN => { answer: a single FQDN, ttl: TTL for this specific answer }
      // Note: Key & Answer must be fully-qualified (ending in dot) and all lowercase
      "www.": {"answer": "web.", "ttl": 42}
    },

    // PTR records
    "ptr": {
      // IP Address => { answer: a single FQDN, ttl: TTL for this specific answer }
      // or
      // FQDN (with backwards octets) => { answer: a single FQDN, ttl: TTL for this specific answer }
      // Note: Key must be fully-qualified (ending in dot) and all lowercase
      "10.42.1.2": {"answer": "mycontainer.discover.internal."},
      "3.1.42.10.in-addr.apra.": {"answer": "anothercontainer.discover.internal."},
    },

    // TXT records
    "txt": {
      // FQDN => { answer: array of strings, ttl: TTL for this specific answer }
      // Note: Key must be fully-qualified (ending in dot) and all lowercase
      // Each individual answer string must be < 255 chars.
      "example.com.": {"ttl": 43, "answer": [
        "v=spf1 ip4:192.168.0.0/16 ~all"
      ]}
    }
  },

  "192.168.0.2": {
    "recurse": ["8.8.4.4:53","8.8.8.8"],
    "a": {
      "mysql.": {"answer": ["192.168.0.3"]},
      "web.": {"answer": ["192.168.0.4","192.168.0.5","192.168.0.6"]}
    },
    "cname": {
      "www.": {"answer": "web."}
    }
  },

  // "default" is a special key that will be checked if no answer is found in a client IP-specific entry
  "default": {
    "recurse": ["8.8.8.8"],
    "a": {
      "foo.": {"answer": ["1.2.3.4"]}
    },
    "cname": {
      "website.": "www.",
      "external.": "rancher.com."
    }
  }
}

Answering queries

A query is answered by returning the first match of:

  • An entry in the answers map for the client's IP.
  • An entry in the answers map in the "default" key.
  • If there is a "recurse" key for the client's IP, perform recursive lookup on each of those servers (in order).
  • If there is a "recurse" key for the "default", perform recursive lookup on each of those servers (in order).
  • Do not pass go, do not collect $200. Return SERVFAIL.

If the result is a CNAME record, then the process is repeated recursively until an A record is found. If the chain does not end in an A record, is more than 10 levels deep, or is circular, an error is returned.

Limitations

  • Only A, CNAME, PTR, and TXT records are currently supported in the local config. Other kinds of records may be returned from recursive responses.

Contact

For bugs, questions, comments, corrections, suggestions, etc., open an issue in rancher/rancher with a title starting with [rancher-dns] .

Or just click here to create a new issue.

License

Copyright (c) 2015 Rancher Labs, Inc.

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.