Create a DNS token

This topic describes how to create a token that enables the Consul DNS to query services in the network when ACLs are enabled.

Introduction

The Consul binary ships with a DNS server that you can use for service discovery in your network. The agent that fulfills DNS lookups requires appropriate ACL permissions to discover services, nodes, and prepared queries registered in Consul.

A Consul agent must be configured with a token linked to policies that grant the appropriate set of permissions.

Specify the default token to the Consul agent to authorize the agent to respond to DNS queries. Refer to DNS usage overview for details on configuring and using Consul DNS.

Requirements

Core ACL functionality is available in all versions of Consul.

The DNS token must be linked to policies that grant the following permissions:

• service:read: Enables the agent to perform service lookups for DNS
• node:read: Enables node lookups over DNS
• query:read: Enables the agent to perform prepared query lookups for DNS

Authentication

You must provide an ACL token linked to a policy with acl:write permissions to create and modify ACL tokens and policies using the CLI or API.

You can provide the token manually using the -token option on the command line, but we recommend setting the CONSUL_HTTP_TOKEN environment variable to simplify your workflow:

$ export CONSUL_HTTP_TOKEN=<acl-token-secret-id>

The Consul CLI automatically reads the CONSUL_HTTP_TOKEN environment variable so that you do not have to pass the token to every Consul CLI command.

To authenticate calls to the Consul HTTP API, you must provide the token in the X-Consul-Token header for each call:

$ curl --header "X-Consul-Token: $CONSUL_HTTP_TOKEN" ...

To learn about alternative ways to authenticate, refer to the following documentation:

• CLI Authentication
• API Authentication

DNS token in Consul CE

To create a token for DNS, you must define a policy, register the policy with Consul, and link the policy to a token.

Define a policy

You can send policy definitions as command line or API arguments or define them in an external HCL or JSON file. Refer to ACL Rules for details about all of the rules you can use in your policies.

The following example policy is defined in a file. The policy grants the appropriate permissions to enable a Consul agent to respond to DNS queries.

node_prefix "" {
  policy = "read"
}
service_prefix "" {
  policy = "read"
}
query_prefix "" {
  policy = "read"
}

{
  "node_prefix": {
    "": [{
      "policy": "read"
    }]
  },
  "query_prefix": {
    "": [{
      "policy": "read"
    }]
  },
  "service_prefix": {
    "": [{
      "policy": "read"
    }]
  }
}

Register the policy with Consul

After defining the policy, you can register the policy with Consul using the command line or API endpoint.

$ consul acl policy create \
    -name "dns-access" -rules @dns-access.hcl \
    -description "DNS Policy"

$ curl --request PUT http://127.0.0.1:8500/v1/acl/policy \
  --header "X-Consul-Token: $CONSUL_HTTP_TOKEN" \
  --data '{
  "Name": "dns-access",
  "Description": "DNS Policy",
  "Rules": "node_prefix \"\" {\n  policy = \"read\"\n}\nservice_prefix \"\" {\n  policy = \"read\"\n}\nquery_prefix \"\" {\n  policy = \"read\"\n}\n"
}'

Link the policy to a token

After registering the policy into Consul, you can create and link tokens using the Consul command line or API endpoint. You can also enable Consul to dynamically create tokens from trusted external systems using an auth method.

$ consul acl token create \
    -description "DNS token" \
    -policy-name "dns-access"

$ curl --request PUT http://127.0.0.1:8500/v1/acl/token \
  --header "X-Consul-Token: $CONSUL_HTTP_TOKEN" \
  --data '{
  "Policies": [
    {
      "Name": "dns-access"
    }
  ]
}'

DNS token in Consul Enterprise

To create a token for DNS, you must define a policy, register the policy with Consul, and link the policy to a token.

Define a policy

You can send policy definitions as command line or API arguments or define them in an external HCL or JSON file. Refer to ACL Rules for details about all of the rules you can use in your policies.

The following example policy is defined in a file. The policy grants the appropriate permissions to enable a Consul agent to respond to DNS queries for resources in any namespace in any partition.

partition "default" {
    namespace "default" {
        query_prefix "" {
            policy = "read"
        }
    }
}
partition_prefix "" {
  namespace_prefix "" {
    node_prefix "" {
      policy = "read"
    }
    service_prefix "" {
      policy = "read"
    }
  }
}

{
  "partition": {
    "default": [{
      "namespace": {
        "default": [{
          "query_prefix": {
            "": [{
              "policy": "read"
            }]
          }
        }]
      }
    }]
  },
  "partition_prefix": {
    "": [{
      "namespace_prefix": {
        "": [{
          "node_prefix": {
            "": [{
              "policy": "read"
            }]
          },
          "service_prefix": {
            "": [{
              "policy": "read"
            }]
          }
        }]
      }
    }]
  }
}

Register the policy with Consul

After defining the policy, you can register the policy with Consul using the command line or API endpoint.

You can specify an admin partition when creating policies in Consul Enterprise. The policy is only valid in the specified admin partition. The example policy contains permissions for multiple namespaces in multiple partitions. You must create ACL policies that grant permissions for multiple namespaces in multiple partitions in the default namespace and the default partition.

consul acl policy create -partition "default" -namespace "default" \
  -name dns-access -rules @dns-access.hcl \
  -description "DNS Policy"

$ curl --request PUT http://127.0.0.1:8500/v1/acl/policy \
  --header "X-Consul-Token: $CONSUL_HTTP_TOKEN" \
  --data '{
  "Name": "dns-access",
  "Description": "DNS Policy",
  "Partition": "default",
  "Namespace": "default",
  "Rules": "partition_prefix \"\" {\n  namespace_prefix \"\" {\n    node_prefix \"\" {\n      policy = \"read\"\n    }\n    service_prefix \"\" {\n      policy = \"read\"\n    }\n    query_prefix \"\" {\n      policy = \"read\"\n    }\n  }\n}\n"
}'

Link the policy to a token

After registering the policy into Consul, you can create and link tokens using the Consul command line or API endpoint. You can also enable Consul to dynamically create tokens from trusted external systems using an auth method.

$ consul acl token create -partition "default" -namespace "default" \
    -description "DNS token" \
    -policy-name "dns-access"

$ curl --request PUT http://127.0.0.1:8500/v1/acl/token \
  --header "X-Consul-Token: $CONSUL_HTTP_TOKEN" \
  --data '{
  "Policies": [
    {
      "Name": "dns-access"
    }
  ],
  "Partition": "default",
  "Namespace": "default"
}'

Apply the token

Configure the Consul agent with the token by either specifying the token in the agent configuration file or by using the consul set-agent-token command.

Apply the token in a file

Specify the token in the default field of the agent configuration file so that the agent can present it and register into the catalog on startup.

acl = {
  enabled = true
  tokens = {
    default = "<token>"
    ...
  }
  ...
}

Apply the token with a command

Set the default token using the acl.token.default command. The following command configures a running Consul agent token with the specified token.

$ consul set-agent-token default <acl-token-secret-id>