---
layout: docs
page_title: Access Control List (ACL) Overview
description: >-
  This topic describes provides an overview of the optional access control list (ACL) system shipped with Consul. The ACL system authenticates requests and authorizes access to resources. It is used by the UI, API, and CLI for service-to-service communication and agent-to-agent communication.
---

# Access Control List (ACL) Overview

This topic describes core concepts associated with the optional access control list (ACL) system shipped with Consul. ACLs authenticate requests and authorize access to resources. They also control access to the Consul UI, API, and CLI, as well as secure service-to-service and agent-to-agent communication.

Refer to the following tutorials for step-by-step instructions on how to get started using ACLs:

- [Bootstrap and Explore ACLs]
- [Secure Consul with ACLs]
- [Troubleshoot the ACL System](https://learn.hashicorp.com/tutorials/consul/access-control-troubleshoot)

[bootstrap and explore acls]: https://learn.hashicorp.com/tutorials/consul/access-control-setup?utm_source=consul.io&utm_medium=docs
[secure consul with acls]: https://learn.hashicorp.com/tutorials/consul/access-control-setup-production?utm_source=consul.io&utm_medium=docs

Refer to the [ACL API reference](/api-docs/acl) and [ACL CLI reference](/commands/acl) for additional usage information.

## Workflow Overview

Implementations may vary depending on the needs of the organization, but the following procedure describes the basic workflow for for creating and implementing ACLs:

1. The person responsible for administrating ACLs in your organization specifies one or more authentication rules to define a [policy](#policies).
1. The ACL administrator uses the Consul API to generate and link a [token](#tokens) to one or more policies. The following diagram illustrates the relationship between rules, policies, and tokens:

  ![ACL system component relationships](/img/acl-token-policy-rule-relationship.png)

  The ACL administrator can create and link additional artifacts to tokens, such as [service identities](#service-identities), [node identities](#node-identities), and [roles](#roles) that enable policies to accommodate more complex requirements.

1. Tokens are distributed to end users and incorporated into their services.
1. Agents and services present the token when making requests.
1. Consul evaluates the token to determine if the request has permission to interact with the requested resource.

## Tokens

ACL tokens are the core method of authentication in Consul. Tokens contain several attributes, but the value of the `SecretID` field (sometimes referred to as the ACL token) is the attribute that you or your service must include to identify the person or system making the request. Your ACL administrator may also use the token's `AccessorID` for audit logging purposes.

Refer to the following topics for details about tokens:

- [Tokens](/docs/security/acl/acl-tokens)
- [ACL token command line](/commands/acl/token)
- [ACL tokens API](/api-docs/acl/tokens)

## Policies

An ACL policy is a set of rules that grant or deny access to resources in the network.
The person responsible for administrating ACLs in your organization will assemble and create policies and link them to tokens.
Tokens are the artifacts distributed to users so that they can be implemented.
In addition to the rules that authenticate access to services, several attributes may be assigned policies that determine their scope.

Refer to the following topics for details about policies:

- [Policies](/docs/security/acl/acl-policies)
- [ACL policy command line](/commands/acl/policy)
- [ACL policy API](/api-docs/acl/policies)

## Roles

A role is a collection of policies that your ACL administrator can link to a token.
They enable you to reuse policies by decoupling the policies from the token distributed to team members.
Instead, the token is linked to the role, which is able to hold several policies that can be updated asynchronously without distributing new tokens to users.
As a result, roles can provide a more convenient authentication infrastructure than creating unique policies and tokens for each requester.

Refer to the [Roles](/docs/security/acl/acl-roles) topic for additional information.

## Service Identities

Service identities are configuration blocks that you can add to role configurations or specify when linking tokens to policies. You can use them during the authorization process to automatically generate a policy for specific services. The policy is linked to the role or token, allowing the services to be discovered and to discover other healthy service instances in a service mesh.

Service identities enable you to quickly construct policies for services, rather than creating identical polices for each service.

Refer to the following topics for additional information about service identities:

- [Service Identities](/docs/security/acl/acl-roles#service-identities)
- [API documentation for roles](/api-docs/acl/roles#sample-payload)

## Node Identities

Node identities are configuration blocks that you can add to role configurations or specify when linking tokens to policies. You can use them during the authorization process to automatically generate a policy for specific nodes. When you configure the agent, you can specify the token linked to the policy with [`acl_tokens_agent`](/docs/agent/options#acl_tokens_agent).

Use node identities to quickly construct policies for multiple nodes, rather than creating identical polices for each individual node.

Refer to the following topics for additional information about node identities:

- [Node Identities](/docs/security/acl/acl-roles#node-identities)
- [API documentation for roles](/api-docs/acl/roles#sample-payload)