Access Control List (ACL)

The Nomad ACL system is designed to be intuitive, high-performance, and to provide administrative insight. At the highest level, there are four major components to the ACL system: tokens, policies, roles, and capabilities. The two components named auth methods and binding rules are specific to Nomad's Single Sign-On (SSO) ACL capabilities.

The Nomad access control tutorials provide detailed information and guidance on Nomad ACL system.

Policy

Policies consist of a set of rules defining the capabilities or actions to be granted. For example, a readonly policy might only grant the ability to list and inspect running jobs, but not to submit new ones. No permissions are granted by default, making Nomad a default-deny system.

Each policy comprises one or more rules. The rules define the capabilities of a Nomad ACL token for accessing the objects in a Nomad cluster, objects like namespaces, node, agent, operator, quota, etc. For more information on writing policies, see the ACL policy reference doc.

Role

Roles group one or more ACL policies into a container which can then be used to generate ACL tokens for authorisation. This abstraction allows easier control and updating of ACL permissions, particularly in larger, more diverse clusters.

Token

Requests to Nomad are authenticated using a bearer token. Each ACL token has a public Accessor ID which is used to name a token and a Secret ID which is used to make requests to Nomad. The Secret ID is provided using a request header (X-Nomad-Token) and is used to authenticate the caller. Tokens are either management or client types. The management tokens are effectively "root" in the system and can perform any operation. The client tokens are associated with one or more ACL policies or roles which grant specific capabilities.

When ACL tokens are created, they can be optionally marked as Global. This causes them to be created in the authoritative region and replicated to all other regions. Otherwise, tokens are created locally in the region the request was made and not replicated. Local tokens cannot be used for cross-region requests since they are not replicated between regions.

Workload Identity

Nomad allocations can receive workload identities in the form of a JSON Web Token (JWT). The Workload Identity concept page has more information on this topic.

Auth Method

Authentication methods dictate how Nomad should talk to SSO providers when a user requests to authenticate using one. Currently, Nomad supports the OpenID Connect (OIDC) SSO workflow which allows users to log in to Nomad via applications such as Auth0, Okta, and Vault, and non-interactive login via externally-issued JSON Web Tokens (JWT).

Binding Rule

Binding rules provide a mapping between a Nomad user's SSO authorisation claims and internal Nomad objects such as ACL Roles and ACL Policies. A binding rule is directly related to a single auth method, and therefore only evaluated by login attempts using that method. All binding rules mapped to an auth method are evaluated during each login attempt.

A successful selector match between an SSO provider claim and a binding rule will result in the generated ACL token having the identified ACL role or policy assigned to it. If the BindType parameter is management, the ACL token generated will be a management token, rather than a client token. This matcher supersedes role or policy assignments, and therefore should be used with caution.

Replication

Multi-region federated clusters run replication process to replicate ACL objects from the authoritative region. The replication processes run on each federated leader and replicate ACL policies, roles, auth methods, binding rules, and token marked as Global.