Kevin Simper 759e535f54 Updating dns forwarding

It is not really clear that you only have to do one of the following and not all three.

2016-01-14 22:53:14 +01:00

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layout	page_title	sidebar_current	description
docs	Forwarding	docs-guides-forwarding	By default, DNS is served from port 53. On most operating systems, this requires elevated privileges. Instead of running Consul with an administrative or root account, it is possible to instead forward appropriate queries to Consul, running on an unprivileged port, from another DNS server.

Forwarding DNS

By default, DNS is served from port 53. On most operating systems, this requires elevated privileges. Instead of running Consul with an administrative or root account, it is possible to instead forward appropriate queries to Consul, running on an unprivileged port, from another DNS server.

In this guide, we will demonstrate forwarding from BIND as well as dnsmasq. For the sake of simplicity, BIND and Consul are running on the same machine in this example, but this is not required.

It is worth mentioning that, by default, Consul does not resolve DNS records outside the .consul. zone unless the recursors configuration option has been set. As an example of how this changes Consul's behavior, suppose a Consul DNS reply includes a CNAME record pointing outside the .consul TLD. The DNS reply will only include CNAME records by default. By contrast, when recursors is set and the upstream resolver is functioning correctly, Consul will try to resolve CNAMEs and include any records (e.g. A, AAAA, PTR) for them in its DNS reply.

You can either do one of the following:

BIND Setup

First, you have to disable DNSSEC so that Consul and BIND can communicate. Here is an example of such a configuration:

options {
  listen-on port 53 { 127.0.0.1; };
  listen-on-v6 port 53 { ::1; };
  directory       "/var/named";
  dump-file       "/var/named/data/cache_dump.db";
  statistics-file "/var/named/data/named_stats.txt";
  memstatistics-file "/var/named/data/named_mem_stats.txt";
  allow-query     { localhost; };
  recursion yes;

  dnssec-enable no;
  dnssec-validation no;

  /* Path to ISC DLV key */
  bindkeys-file "/etc/named.iscdlv.key";

  managed-keys-directory "/var/named/dynamic";
};

include "/etc/named/consul.conf";

Zone File

Then we set up a zone for our Consul managed records in consul.conf:

zone "consul" IN {
  type forward;
  forward only;
  forwarders { 127.0.0.1 port 8600; };
};

Here we assume Consul is running with default settings and is serving DNS on port 8600.

Dnsmasq Setup

Dnsmasq is typically configured via files in the /etc/dnsmasq.d directory. To configure Consul, create the file /etc/dnsmasq.d/10-consul with the following contents:

server=/consul/127.0.0.1#8600

Once that configuration is created, restart the dnsmasq service.

Testing

First, perform a DNS query against Consul directly to be sure that the record exists:

[root@localhost ~]# dig @localhost -p 8600 master.redis.service.dc-1.consul. A

; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.23.rc1.32.amzn1 <<>> @localhost master.redis.service.dc-1.consul. A
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 11536
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;master.redis.service.dc-1.consul. IN A

;; ANSWER SECTION:
master.redis.service.dc-1.consul. 0 IN A 172.31.3.234

;; Query time: 4 msec
;; SERVER: 127.0.0.1#53(127.0.0.1)
;; WHEN: Wed Apr  9 17:36:12 2014
;; MSG SIZE  rcvd: 76

Then run the same query against your BIND instance and make sure you get a result:

[root@localhost ~]# dig @localhost -p 53 master.redis.service.dc-1.consul. A

; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.23.rc1.32.amzn1 <<>> @localhost master.redis.service.dc-1.consul. A
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 11536
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;master.redis.service.dc-1.consul. IN A

;; ANSWER SECTION:
master.redis.service.dc-1.consul. 0 IN A 172.31.3.234

;; Query time: 4 msec
;; SERVER: 127.0.0.1#53(127.0.0.1)
;; WHEN: Wed Apr  9 17:36:12 2014
;; MSG SIZE  rcvd: 76

Troubleshooting

If you don't get an answer from BIND but you do get an answer from Consul, your best bet is to turn on BIND's query log to see what's happening:

[root@localhost ~]# rndc querylog
[root@localhost ~]# tail -f /var/log/messages

The log may show errors like this:

error (no valid RRSIG) resolving
error (no valid DS) resolving

This indicates that DNSSEC is not disabled properly.

If you see errors about network connections, verify that there are no firewall or routing problems between the servers running BIND and Consul.

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