tls Block

The tls block configures Nomad's TLS communication via HTTP and RPC to enforce secure cluster communication between servers, clients, and between. Note that in most cases, this is mutual TLS (mTLS) where both ends of the connection authenticate each other. The Nomad documentation will typically use "TLS" to refer to this communication except when it is potentially ambiguous between TLS and mTLS.

tls {
  http = true
  rpc  = true
}

This section of the documentation only covers the configuration options for tls block. To understand how to setup the certificates themselves, please see the Enable TLS Encryption for Nomad Tutorial.

tls Parameters

• ca_file (string: "") - Specifies the path to the CA certificate to use for Nomad's TLS communication.

• cert_file (string: "") - Specifies the path to the certificate file used for Nomad's TLS communication.

• key_file (string: "") - Specifies the path to the key file to use for Nomad's TLS communication.

• http (bool: false) - Specifies if TLS should be enabled on the HTTP endpoints on the Nomad agent, including the API. By default this is non-mutual TLS. You can upgrade this to mTLS by setting verify_https_client=true, but this can complicate using the Nomad UI by requiring mTLS in your browser or running a proxy in front of the Nomad UI.

• rpc (bool: false) - Toggle the option to enable mTLS on the RPC endpoints and Raft traffic. When this setting is activated, it establishes protection both between Nomad servers and from the clients back to the servers, ensuring mutual authentication. Setting rpc=true is required for secure operation of Nomad.

• rpc_upgrade_mode (bool: false) - This option should be used only when the cluster is being upgraded to TLS, and removed after the migration is complete. This allows the agent to accept both TLS and plaintext traffic.

• tls_cipher_suites (string: "") - Specifies the TLS cipher suites that will be used by the agent as a comma-separated string. Known insecure ciphers are disabled (3DES and RC4). By default, an agent is configured to use TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384, TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384, TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305, TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305, TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256, TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256, TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384, TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384, TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256 and TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256.

  Nomad does not accept explicit ciphersuite configuration when for TLS 1.3 because the Go team has already designated a select set of ciphers that align with the broadly-accepted Mozilla Security/Server Side TLS guidance for modern TLS configuration.

• tls_min_version (string: "tls12")- Specifies the minimum supported version of TLS. Accepted values are "tls10", "tls11", "tls12", "tls13".

• tls_prefer_server_cipher_suites (bool: false) - Specifies whether TLS connections should prefer the server's ciphersuites over the client's.

• verify_https_client (bool: false) - Specifies agents should require client certificates for all incoming HTTPS requests, effectively upgrading tls.http=true to mTLS. The client certificates must be signed by the same CA as Nomad. By default, verify_https_client is set to false, which is safe so long as ACLs are enabled. This is recommended if you are using the Nomad web UI to avoid the difficulty of distributing client certs to browsers.

• verify_server_hostname (bool: false) - Specifies if outgoing TLS connections should verify the server's hostname.

tls Examples

The following examples only show the tls blocks. Remember that the tls block is only valid in the placements listed above.

Enabling TLS

This example shows enabling TLS configuration. This enables mTLS communication between all servers and clients using the default system CA bundle and certificates.

tls {
  http = true
  rpc  = true

  ca_file   = "/etc/certs/ca.crt"
  cert_file = "/etc/certs/nomad.crt"
  key_file  = "/etc/certs/nomad.key"
}

tls Configuration Reloads

Nomad supports dynamically reloading both client and server TLS configuration. To reload an agent's TLS configuration, first update the TLS block in the agent's configuration file and then send the Nomad agent a SIGHUP signal. Note that this will only reload a subset of the configuration file, including the TLS configuration.

The agent reloads all its network connections when there are changes to its TLS configuration during a config reload via SIGHUP. Any new connections established will use the updated configuration, and any outstanding old connections will be closed. This process works when upgrading to TLS, downgrading from it, as well as rolling certificates.