--- layout: "docs" page_title: "ACL Rules" sidebar_current: "docs-acl-rules" description: |- Consul provides an optional Access Control List (ACL) system which can be used to control access to data and APIs. The ACL system is a Capability-based system that relies on tokens which can have fine grained rules applied to them. It is very similar to AWS IAM in many ways. --- -> **1.4.0 and later:** This document only applies in Consul versions 1.4.0 and later. The documentation for the legacy ACL system is [here](/docs/acl/acl-legacy.html) # ACL Rules Consul provides an optional Access Control List (ACL) system which can be used to control access to data and APIs. To learn more about Consul's ACL review the [ACL system documentation](/docs/acl/acl-system.html) A core part of the ACL system is the rule language, which is used to describe the policy that must be enforced. There are two types of rules: prefix based rules and exact matching rules. ## Rule Specification Rules are composed of a resource, a segment (for some resource areas) and a policy disposition. The general structure of a rule is: ```text "" { policy = "" } ``` Segmented resource areas allow operators to more finely control access to those resources. Note that not all resource areas are segmented such as the `keyring`, `operator`, and `acl` resources. For those rules they would look like: ```text = "" ``` Policies can have several control levels: * `read`: allow the resource to be read but not modified. * `write`: allow the resource to be read and modified. * `deny`: do not allow the resource to be read or modified. * `list`: allows access to all the keys under a segment in the Consul KV. Note, this policy can only be used with the `key_prefix` resource and [`acl.enable_key_list_policy`](/docs/agent/options.html#acl_enable_key_list) must be set to true. When using prefix-based rules, the most specific prefix match determines the action. This allows for flexible rules like an empty prefix to allow read-only access to all resources, along with some specific prefixes that allow write access or that are denied all access. Exact matching rules will only apply to the exact resource specified. The order of precedence for matching rules are, DENY has priority over WRITE or READ and WRITE has priority over READ. We make use of the [HashiCorp Configuration Language (HCL)](https://github.com/hashicorp/hcl/) to specify rules. This language is human readable and interoperable with JSON making it easy to machine-generate. Rules can make use of one or more policies. Specification in the HCL format looks like: ```hcl # These control access to the key/value store. key_prefix "" { policy = "read" } key_prefix "foo/" { policy = "write" } key_prefix "foo/private/" { policy = "deny" } # Or for exact key matches key "foo/bar/secret" { policy = "deny" } # This controls access to cluster-wide Consul operator information. operator = "read" ``` This is equivalent to the following JSON input: ```json { "key_prefix": { "": { "policy": "read" }, "foo/": { "policy": "write" }, "foo/private/": { "policy": "deny" } }, "key" : { "foo/bar/secret" : { "policy" : "deny" } }, "operator": "read" } ``` The [ACL API](/api/acl/acl.html) allows either HCL or JSON to be used to define the content of the rules section of a policy. Here's a sample request using the HCL form: ```text $ curl \ --request PUT \ --data \ '{ "Name": "my-app-policy", "Rules": "key \"\" { policy = \"read\" } key \"foo/\" { policy = \"write\" } key \"foo/private/\" { policy = \"deny\" } operator = \"read\"" }' http://127.0.0.1:8500/v1/acl/policy?token= ``` Here's an equivalent request using the JSON form: ```text $ curl \ --request PUT \ --data \ '{ "Name": "my-app-policy", "Rules": "{\"key\":{\"\":{\"policy\":\"read\"},\"foo/\":{\"policy\":\"write\"},\"foo/private\":{\"policy\":\"deny\"}},\"operator\":\"read\"}" }' http://127.0.0.1:8500/v1/acl/policy?token= ``` On success, the Policy is returned: ```json { "CreateIndex": 7, "Hash": "UMG6QEbV40Gs7Cgi6l/ZjYWUwRS0pIxxusFKyKOt8qI=", "ID": "5f423562-aca1-53c3-e121-cb0eb2ea1cd3", "ModifyIndex": 7, "Name": "my-app-policy", "Rules": "key \"\" { policy = \"read\" } key \"foo/\" { policy = \"write\" } key \"foo/private/\" { policy = \"deny\" } operator = \"read\"" } ``` The created policy can now be specified either by name or by ID when [creating a token](https://learn.hashicorp.com/consul/security-networking/production-acls#create-the-agent-token). This will grant the rules provided to the [bearer of that token](/api/index.html#authentication). Below is a breakdown of each rule type. #### ACL Resource Rules The `acl` resource controls access to ACL operations in the [ACL API](/api/acl/acl.html). ACL rules look like this: ```hcl acl = "write" ``` There is only one acl rule allowed per policy and its value is set to one of the [policy dispositions](/docs/acl/acl-rules.html#rule-specification). In the example above ACLs may be read or written including discovering any token's secret ID. Snapshotting also requires `acl = "write"` permissions due to the fact that all the token secrets are contained within the snapshot. #### Agent Rules The `agent` and `agent_prefix` resources control access to the utility operations in the [Agent API](/api/agent.html), such as join and leave. All of the catalog-related operations are covered by the [`node` or `node_prefix`](#node-rules) and [`service` or `service_prefix`](#service-rules) policies instead. Agent rules look like this: ```hcl agent_prefix "" { policy = "read" } agent "foo" { policy = "write" } agent_prefix "bar" { policy = "deny" } ``` Agent rules are keyed by the node name they apply to. In the example above the rules allow read-only access to any node name by using the empty prefix, read-write access to the node with the _exact_ name `foo`, and denies all access to any noe name that starts with `bar`. Since [Agent API](/api/agent.html) utility operations may be required before an agent is joined to a cluster, or during an outage of the Consul servers or ACL datacenter, a special token may be configured with [`acl.tokens.agent_master`](/docs/agent/options.html#acl_tokens_agent_master) to allow write access to these operations even if no ACL resolution capability is available. #### Event Rules The `event` and `event_prefix` resources control access to event operations in the [Event API](/api/event.html), such as firing events and listing events. Event rules look like this: ```hcl event_prefix "" { policy = "read" } event "deploy" { policy = "write" } ``` Event rules are segmented by the event name they apply to. In the example above, the rules allow read-only access to any event, and firing of the "deploy" event. The [`consul exec`](/docs/commands/exec.html) command uses events with the "_rexec" prefix during operation, so to enable this feature in a Consul environment with ACLs enabled, you will need to give agents a token with access to this event prefix, in addition to configuring [`disable_remote_exec`](/docs/agent/options.html#disable_remote_exec) to `false`. #### Key/Value Rules The `key` and `key_prefix` resources control access to key/value store operations in the [KV API](/api/kv.html). Key rules look like this: ```hcl key_prefix "" { policy = "read" } key "foo" { policy = "write" } key "bar" { policy = "deny" } ``` Key rules are segmented by the key name they apply to. In the example above, the rules allow read-only access to any key name with the empty prefix rule, allow read-write access to the "foo" key, and deny access to the "bar" key. #### List Policy for Keys Consul 1.0 introduces a new `list` policy for keys that is only enforced when opted in via the boolean config param "acl.enable_key_list_policy". `list` controls access to recursively list entries and keys, and enables more fine grained policies. With "acl.enable_key_list_policy", recursive reads via [the KV API](/api/kv.html#recurse) with an invalid token result in a 403. Example: ```hcl key_prefix "" { policy = "deny" } key_prefix "bar" { policy = "list" } key_prefix "baz" { policy = "read" } ``` In the example above, the rules allow reading the key "baz", and only allow recursive reads on the prefix "bar". A token with `write` access on a prefix also has `list` access. A token with `list` access on a prefix also has `read` access on all its suffixes. #### Sentinel Integration Consul Enterprise supports additional optional fields for key write policies for [Sentinel](https://docs.hashicorp.com/sentinel/app/consul/) integration. An example key rule with a Sentinel code policy looks like this: ```hcl key "foo" { policy = "write" sentinel { code = < Operation Version <= 0.6.3 Version > 0.6.3 Create static query without `Name` The ACL Token used to create the prepared query is checked to make sure it can access the service being queried. This token is captured as the `Token` to use when executing the prepared query. No ACL policies are used as long as no `Name` is defined. No `Token` is captured by default unless specifically supplied by the client when creating the query. Create static query with `Name` The ACL Token used to create the prepared query is checked to make sure it can access the service being queried. This token is captured as the `Token` to use when executing the prepared query. The client token's `query` ACL policy is used to determine if the client is allowed to register a query for the given `Name`. No `Token` is captured by default unless specifically supplied by the client when creating the query. Manage static query without `Name` The ACL Token used to create the query or a token with management privileges must be supplied in order to perform these operations. Any client with the ID of the query can perform these operations. Manage static query with a `Name` The ACL token used to create the query or a token with management privileges must be supplied in order to perform these operations. Similar to create, the client token's `query` ACL policy is used to determine if these operations are allowed. List queries A token with management privileges is required to list any queries. The client token's `query` ACL policy is used to determine which queries they can see. Only tokens with management privileges can see prepared queries without `Name`. Execute query Since a `Token` is always captured when a query is created, that is used to check access to the service being queried. Any token supplied by the client is ignored. The captured token, client's token, or anonymous token is used to filter the results, as described above. #### Service Rules The `service` and `service_prefix` resources control service-level registration and read access to the [Catalog API](/api/catalog.html) and service discovery with the [Health API](/api/health.html). Service rules look like this: ```hcl service_prefix "" { policy = "read" } service "app" { policy = "write" } service "admin" { policy = "deny" } ``` Service rules are segmented by the service name they apply to. In the example above, the rules allow read-only access to any service name with the empty prefix, allow read-write access to the "app" service, and deny all access to the "admin" service. Consul's DNS interface is affected by restrictions on service rules. If the [`acl.tokens.default`](/docs/agent/options.html#acl_tokens_default) used by the agent does not have "read" access to a given service, then the DNS interface will return no records when queried for it. When reading from the catalog or retrieving information from the health endpoints, service rules are used to filter the results of the query. Service rules come into play when using the [Agent API](/api/agent.html) to register services or checks. The agent will check tokens locally as a service or check is registered, and Consul also performs periodic [anti-entropy](/docs/internals/anti-entropy.html) syncs, which may require an ACL token to complete. To accommodate this, Consul provides two methods of configuring ACL tokens to use for registration events: 1. Using the [acl.tokens.default](/docs/agent/options.html#acl_tokens_default) configuration directive. This allows a single token to be configured globally and used during all service and check registration operations. 2. Providing an ACL token with service and check definitions at registration time. This allows for greater flexibility and enables the use of multiple tokens on the same agent. Examples of what this looks like are available for both [services](/docs/agent/services.html) and [checks](/docs/agent/checks.html). Tokens may also be passed to the [HTTP API](/api/index.html) for operations that require them. **Note:** all tokens passed to an agent are persisted on local disk to allow recovery from restarts. See [`-data-dir` flag documentation](/docs/agent/options.html#acl_token) for notes on securing access. In addition to ACLs, in Consul 0.9.0 and later, the agent must be configured with [`enable_script_checks`](/docs/agent/options.html#_enable_script_checks) or [`enable_local_script_checks`](/docs/agent/options.html#_enable_local_script_checks) set to `true` in order to enable script checks. #### Session Rules The `session` and `session_prefix` resources controls access to [Session API](/api/session.html) operations. Session rules look like this: ```hcl session_prefix "" { policy = "read" } session "app" { policy = "write" } session "admin" { policy = "deny" } ``` Session rules are segmented by the node name they apply to. In the example above, the rules allow read-only access to sessions on node name with the empty prefix, allow creating sessions on the node named "app", and deny all access to any sessions on the "admin" node.