open-consul/website/content/docs/discovery/dns.mdx

---
layout: docs
page_title: Find Services - DNS Interface
description: >-
  One of the primary query interfaces for Consul is DNS. The DNS interface
  allows applications to make use of service discovery without any high-touch
  integration with Consul.
---

# DNS Interface

One of the primary query interfaces for Consul is DNS.
The DNS interface allows applications to make use of service
discovery without any high-touch integration with Consul.

For example, instead of making HTTP API requests to Consul,
a host can use the DNS server directly via name lookups
like `redis.service.us-east-1.consul`. This query automatically
translates to a lookup of nodes that provide the `redis` service,
are located in the `us-east-1` datacenter, and have no failing health checks.
It's that simple!

There are a number of configuration options that are important for the DNS interface,
specifically [`client_addr`](/docs/agent/config/config-files#client_addr),[`ports.dns`](/docs/agent/config/config-files#dns_port),
[`recursors`](/docs/agent/config/config-files#recursors),[`domain`](/docs/agent/config/config-files#domain),
[`alt_domain`](/docs/agent/config/config-files#alt_domain), and [`dns_config`](/docs/agent/config/config-files#dns_config).
By default, Consul will listen on 127.0.0.1:8600 for DNS queries in the `consul.`
domain, without support for further DNS recursion. Please consult the
[documentation on configuration options](/docs/agent/config),
specifically the configuration items linked above, for more details.

There are a few ways to use the DNS interface. One option is to use a custom
DNS resolver library and point it at Consul. Another option is to set Consul
as the DNS server for a node and provide a
[`recursors`](/docs/agent/config/config-files#recursors) configuration so that non-Consul queries
can also be resolved. The last method is to forward all queries for the "consul."
domain to a Consul agent from the existing DNS server. Review the
[DNS Forwarding tutorial](https://learn.hashicorp.com/tutorials/consul/dns-forwarding?utm_source=consul.io&utm_medium=docs) for examples.

You can experiment with Consul's DNS server on the command line using tools such as `dig`:

```shell-session
$ dig @127.0.0.1 -p 8600 redis.service.dc1.consul. ANY
```

-> **Note:** In DNS, all queries are case-insensitive. A lookup of `PostgreSQL.node.dc1.consul` will find all nodes named `postgresql`.

## Node Lookups

To resolve names, Consul relies on a very specific format for queries.
There are fundamentally two types of queries: node lookups and service lookups.
A node lookup, a simple query for the address of a named node, looks like this:

```text
<node>.node[.datacenter].<domain>
```

For example, if we have a `foo` node with default settings, we could
look for `foo.node.dc1.consul.` The datacenter is an optional part of
the FQDN: if not provided, it defaults to the datacenter of the agent.
If we know `foo` is running in the same datacenter as our local agent,
we can instead use `foo.node.consul.` This convention allows for terse
syntax where appropriate while supporting queries of nodes in remote
datacenters as necessary.

For a node lookup, the only records returned are A and AAAA records
containing the IP address, and TXT records containing the
`node_meta` values of the node.

```shell-session
$ dig @127.0.0.1 -p 8600 foo.node.consul ANY

; <<>> DiG 9.8.3-P1 <<>> @127.0.0.1 -p 8600 foo.node.consul ANY
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 24355
;; flags: qr aa rd; QUERY: 1, ANSWER: 1, AUTHORITY: 1, ADDITIONAL: 0
;; WARNING: recursion requested but not available

;; QUESTION SECTION:
;foo.node.consul.		IN	ANY

;; ANSWER SECTION:
foo.node.consul.	0	IN	A	10.1.10.12
foo.node.consul.	0	IN	TXT	"meta_key=meta_value"
foo.node.consul.	0	IN	TXT	"value only"


;; AUTHORITY SECTION:
consul.			0	IN	SOA	ns.consul. postmaster.consul. 1392836399 3600 600 86400 0
```

By default the TXT records value will match the node's metadata key-value
pairs according to [RFC1464](https://www.ietf.org/rfc/rfc1464.txt).
Alternatively, the TXT record will only include the node's metadata value when the
node's metadata key starts with `rfc1035-`.

## Service Lookups

A service lookup is used to query for service providers. Service queries support
two lookup methods: standard and strict [RFC 2782](https://tools.ietf.org/html/rfc2782).

By default, SRV weights are all set at 1, but changing weights is supported using the
`Weights` attribute of the [service definition](/docs/discovery/services).

Note that DNS is limited in size per request, even when performing DNS TCP
queries.

For services having many instances (more than 500), it might not be possible to
retrieve the complete list of instances for the service.

When DNS SRV response are sent, order is randomized, but weights are not
taken into account. In the case of truncation different clients using weighted SRV
responses will have partial and inconsistent views of instances weights so the
request distribution could be skewed from the intended weights. In that case,
it is recommended to use the HTTP API to retrieve the list of nodes.

### Standard Lookup

The format of a standard service lookup is:

```text
[tag.]<service>.service[.datacenter].<domain>
```

The `tag` is optional, and, as with node lookups, the `datacenter` is as
well. If no tag is provided, no filtering is done on tag. If no
datacenter is provided, the datacenter of this Consul agent is assumed.

If we want to find any redis service providers in our local datacenter,
we could query `redis.service.consul.` If we want to find the PostgreSQL
primary in a particular datacenter, we could query
`primary.postgresql.service.dc2.consul.`

The DNS query system makes use of health check information to prevent routing
to unhealthy nodes. When a service query is made, any services failing their health
check or failing a node system check will be omitted from the results. To allow
for simple load balancing, the set of nodes returned is also randomized each time.
These mechanisms make it easy to use DNS along with application-level retries
as the foundation for an auto-healing service oriented architecture.

For standard services queries, both A and SRV records are supported. SRV records
provide the port that a service is registered on, enabling clients to avoid relying
on well-known ports. SRV records are only served if the client specifically requests
them, like so:

```shell-session
$ dig @127.0.0.1 -p 8600 consul.service.consul SRV

; <<>> DiG 9.8.3-P1 <<>> @127.0.0.1 -p 8600 consul.service.consul ANY
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 50483
;; flags: qr aa rd; QUERY: 1, ANSWER: 3, AUTHORITY: 1, ADDITIONAL: 1
;; WARNING: recursion requested but not available

;; QUESTION SECTION:
;consul.service.consul.		IN	SRV

;; ANSWER SECTION:
consul.service.consul.	0	IN	SRV	1 1 8300 foobar.node.dc1.consul.

;; ADDITIONAL SECTION:
foobar.node.dc1.consul.	0	IN	A	10.1.10.12
```

### RFC 2782 Lookup

The format for RFC 2782 SRV lookups is:

    _<service>._<protocol>[.service][.datacenter][.domain]

Per [RFC 2782](https://tools.ietf.org/html/rfc2782), SRV queries should use
underscores, `_`, as a prefix to the `service` and `protocol` values in a query to
prevent DNS collisions. The `protocol` value can be any of the tags for a
service. If the service has no tags, `tcp` should be used. If `tcp`
is specified as the protocol, the query will not perform any tag filtering.

Other than the query format and default `tcp` protocol/tag value, the behavior
of the RFC style lookup is the same as the standard style of lookup.

If you registered the service `rabbitmq` on port 5672 and tagged it with `amqp`,
you could make an RFC 2782 query for its SRV record as `_rabbitmq._amqp.service.consul`:

```shell-session
$ dig @127.0.0.1 -p 8600 _rabbitmq._amqp.service.consul SRV

; <<>> DiG 9.8.3-P1 <<>> @127.0.0.1 -p 8600 _rabbitmq._amqp.service.consul ANY
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 52838
;; flags: qr aa rd; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1
;; WARNING: recursion requested but not available

;; QUESTION SECTION:
;_rabbitmq._amqp.service.consul.	IN	SRV

;; ANSWER SECTION:
_rabbitmq._amqp.service.consul.	0	IN	SRV	1 1 5672 rabbitmq.node1.dc1.consul.

;; ADDITIONAL SECTION:
rabbitmq.node1.dc1.consul.	0	IN	A	10.1.11.20
```

Again, note that the SRV record returns the port of the service as well as its IP.

#### SRV response for hosts in the .addr subdomain

If a service registered to Consul has an explicit IP [`address`](/api-docs/agent/service#address)
or tagged address(es) defined on the service registration, the hostname returned
in the target field of the answer section for the DNS SRV query for the service
will be in the format of `<hexadecimal-encoded IP>.addr.<datacenter>.consul`.

<Tabs>

<Tab heading="IPv4">

In the example below, the `rabbitmq` service has been registered with an explicit
IPv4 address of `192.0.2.10`.

<CodeTabs heading="Service defined with explicit IPv4 address in agent config" filename="agent-config.hcl">

```hcl
node_name = "node1"

services {
  name = "rabbitmq"
  address = "192.0.2.10"
  port = 5672
}
```

```json
{
  "node_name": "node1",
  "services": [
    {
      "name": "rabbitmq",
      "address": "192.0.2.10",
      "port": 5672
    }
  ]
}
```

</CodeTabs>

When performing an SRV query for this service, the SRV response contains a single
record with a hostname in the format of `<hexadecimal-encoded IP>.addr.<datacenter>.consul`.

```shell-session
$ dig @127.0.0.1 -p 8600 -t srv _rabbitmq._tcp.service.consul +short
1 1 5672 c000020a.addr.dc1.consul.
```

In this example, the hex-encoded IP from the returned hostname is `c000020a`.
Converting each hex octet to decimal reveals the IP address that was specified
in the service registration.

```shell-session
$ echo -n "c000020a" | perl -ne 'printf("%vd\n", pack("H*", $_))'
192.0.2.10
```

</Tab>

<Tab heading="IPv6">

In the example below, the `rabbitmq` service has been registered with an explicit
IPv6 address of `2001:db8:1:2:cafe::1337`.

<CodeTabs heading="Service defined with explicit IPv6 address in agent config" filename="agent-config.hcl">

```hcl
node_name = "node1"

services {
  name = "rabbitmq"
  address = "2001:db8:1:2:cafe::1337"
  port = 5672
}
```

```json
{
  "node_name": "node1",
  "services": [
    {
      "name": "rabbitmq",
      "address": "2001:db8:1:2:cafe::1337",
      "port": 5672
    }
  ]
}
```

</CodeTabs>

When performing an SRV query for this servie, the SRV response contains a single
record with a hostname in the format of `<hexadecimal-encoded IP>.addr.<datacenter>.consul`.

```shell-session
$ dig @127.0.0.1 -p 8600 -t srv _rabbitmq._tcp.service.consul +short
1 1 5672 20010db800010002cafe000000001337.addr.dc1.consul.
```

In this example, the hex-encoded IP from the returned hostname is
`20010db800010002cafe000000001337`. This is the fully expanded IPv6 address with
colon separators removed.

The following command re-adds the colon separators to display the fully expanded
IPv6 address that was specified in the service registration.

```shell-session
$ echo -n "20010db800010002cafe000000001337" | perl -ne 'printf join(":", unpack("(A4)*", $_))."\n"'
2001:0db8:0001:0002:cafe:0000:0000:1337
```

</Tab>

</Tabs>

### Prepared Query Lookups

The format of a prepared query lookup is:

```text
<query or name>.query[.datacenter].<domain>
```

The `datacenter` is optional, and if not provided, the datacenter of this Consul
agent is assumed.

The `query or name` is the ID or given name of an existing
[Prepared Query](/api-docs/query). These behave like standard service
queries but provide a much richer set of features, such as filtering by multiple
tags and automatically failing over to look for services in remote datacenters if
no healthy nodes are available in the local datacenter. Consul 0.6.4 and later also
added support for [prepared query templates](/api-docs/query#prepared-query-templates)
which can match names using a prefix match, allowing one template to apply to
potentially many services.

To allow for simple load balancing, the set of nodes returned is randomized each time.
Both A and SRV records are supported. SRV records provide the port that a service is
registered on, enabling clients to avoid relying on well-known ports. SRV records are
only served if the client specifically requests them.

### Connect-Capable Service Lookups

To find Connect-capable services:

```text
<service>.connect.<domain>
```

This will find all [Connect-capable](/docs/connect)
endpoints for the given `service`. A Connect-capable endpoint may be
both a proxy for a service or a natively integrated Connect application.
The DNS interface does not differentiate the two.

Most services will use a [proxy](/docs/connect/proxies) that handles
service discovery automatically and therefore won't use this DNS format.
This DNS format is primarily useful for [Connect-native](/docs/connect/native)
applications.

This endpoint currently only finds services within the same datacenter
and doesn't support tags. This DNS interface will be expanded over time.
If you need more complex behavior, please use the
[catalog API](/api-docs/catalog).

### Service Virtual IP Lookups

To find the unique virtual IP allocated for a service:

```text
<service>.virtual.<domain>
```

This will return the unique virtual IP for any [Connect-capable](/docs/connect)
service. Each Connect service has a virtual IP assigned to it by Consul - this is used
by sidecar proxies for the [Transparent Proxy](/docs/connect/transparent-proxy) feature.

The virtual IP is also added to the service's [Tagged Addresses](/docs/discovery/services#tagged-addresses)
under the `consul-virtual` tag.

### Ingress Service Lookups

To find ingress-enabled services:

```text
<service>.ingress.<domain>
```

This will find all [ingress gateway](/docs/connect/gateways/ingress-gateway)
endpoints for the given `service`.

This endpoint currently only finds services within the same datacenter
and doesn't support tags. This DNS interface will be expanded over time.
If you need more complex behavior, please use the
[catalog API](/api-docs/catalog).

### UDP Based DNS Queries

When the DNS query is performed using UDP, Consul will truncate the results
without setting the truncate bit. This is to prevent a redundant lookup over
TCP that generates additional load. If the lookup is done over TCP, the results
are not truncated.

## Alternative Domain

By default, Consul responds to DNS queries in the `consul` domain,
but you can set a specific domain for responding to DNS queries by configuring the [`domain`](/docs/agent/config/config-files#domain) parameter.

In some instances, Consul may need to respond to queries in more than one domain,
such as during a DNS migration or to distinguish between internal and external queries.

Consul versions 1.5.2+ can be configured to respond to DNS queries on an alternative domain
through the [`alt_domain`](/docs/agent/config/config-files#alt_domain) agent configuration
option. As of Consul versions 1.11.0+, Consul's DNS response will use the same domain as was used in the query;
in prior versions, the response may use the primary [`domain`](/docs/agent/config/config-files#domain) no matter which
domain was used in the query.

In the following example, the `alt_domain` parameter is set to `test-domain`:

```hcl
 alt_domain = "test-domain"
```

```shell-session
$ dig @127.0.0.1 -p 8600 consul.service.test-domain SRV
```

The following responses are returned:

```
;; QUESTION SECTION:
;consul.service.test-domain.	IN	SRV

;; ANSWER SECTION:
consul.service.test-domain. 0	IN	SRV	1 1 8300 machine.node.dc1.test-domain.

;; ADDITIONAL SECTION:
machine.node.dc1.test-domain. 0	IN	A	127.0.0.1
machine.node.dc1.test-domain. 0	IN	TXT	"consul-network-segment="
```

-> **PTR queries:** Responses to PTR queries (`<ip>.in-addr.arpa.`) will always use the
[primary domain](/docs/agent/config/config-files#domain) (not the alternative domain),
as there is no way for the query to specify a domain.

## Caching

By default, all DNS results served by Consul set a 0 TTL value. This disables
caching of DNS results. However, there are many situations in which caching is
desirable for performance and scalability. This is discussed more in the tutorial
for [DNS caching](https://learn.hashicorp.com/tutorials/consul/dns-caching).

## WAN Address Translation

By default, Consul DNS queries will return a node's local address, even when
being queried from a remote datacenter. If you need to use a different address
to reach a node from outside its datacenter, you can configure this behavior
using the [`advertise-wan`](/docs/agent/config/cli-flags#_advertise-wan) and
[`translate_wan_addrs`](/docs/agent/config/config-files#translate_wan_addrs) configuration
options.

## Namespaced/Partitioned Services <EnterpriseAlert inline />

Consul Enterprise supports resolving namespaced and partitioned services via DNS.
To maintain backwards compatibility existing queries can be used and these will
resolve services within the `default` namespace and partition. However, for resolving
services from other namespaces or partitions the following form can be used:

```text
[tag.]<service>.service.<namespace>.ns.<partition>.ap.<datacenter>.dc.<domain>
```

This is the canonical name of a Consul Enterprise service. Currently all parts must be
present - in a future version (once the
[`prefer_namespace` configuration](/docs/agent/config/config-files#dns_prefer_namespace) has been
deprecated), the namespace, partition and datacenter components will become optional
and may be individually omitted to default to the `default` namespace, local partition
or local datacenter respectively.

## DNS with ACLs

In order to use the DNS interface when
[Access Control Lists (ACLs)](/docs/security/acl/acl-system)
are enabled, you must first create ACL tokens with the necessary policies.

Consul agents resolve DNS requests using one of the preconfigured tokens below,
listed in order of precedence:

1. The agent's [`default` token](/docs/agent/config/config-files#acl_tokens_default).
2. The built-in [`anonymous` token](/docs/security/acl/acl-system#builtin-tokens).
   Because the anonymous token is used when any request is made to Consul without
   explicitly specifying a token, production deployments should not apply policies
   needed for DNS to this token.

Consul will either accept or deny the request depending on whether the token
has the appropriate authorization. The following table describes the available
DNS lookups and required policies when ACLs are enabled:

| Lookup                                                                         | Type                                               | Description                                                                                                                                                                       | ACLs Required                                                                                                                                                                           |
| ------------------------------------------------------------------------------ | -------------------------------------------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `*.node.consul`                                                                | [Node](#node-lookups)                              | Allow resolving DNS requests for the target node (i.e., `<target>.node.consul`)                                                                                                   | [`node:read`](/docs/security/acl/acl-rules#node-rules)                                                                                                                                  |
| `*.service.consul`, `*.connect.consul`, `*.ingress.consul`, `*.virtual.consul` | [Service: standard](#service-lookups)              | Allow resolving DNS requests for target service (e.g., `<target>.service.consul`) instances running on ACL-authorized nodes                                                       | [`service:read`](/docs/security/acl/acl-rules#service-rules), [`node:read`](/docs/security/acl/acl-rules#node-rules)                                                                    |
| `*.query.consul`                                                               | [Service: prepared query](#prepared-query-lookups) | Allow resolving DNS requests for [service instances specified](/api-docs/query#service-1) by the target prepared query (i.e., `<target>.query.consul`) running on ACL-authorized nodes | [`query:read`](/docs/security/acl/acl-rules#prepared-query-rules), [`service:read`](/docs/security/acl/acl-rules#service-rules), [`node:read`](/docs/security/acl/acl-rules#node-rules) |

For guidance on how to configure an appropriate token for DNS, refer to the
securing Consul with ACLs guides for:

- [Production Environments](https://learn.hashicorp.com/tutorials/consul/access-control-setup-production#token-for-dns)
- [Development Environments](https://learn.hashicorp.com/tutorials/consul/access-control-setup#additional-acl-configuration)