---
layout: docs
page_title: tls Block - Agent Configuration
description: |-
  The "tls" block configures Nomad's TLS communication via HTTP and RPC to
  enforce secure cluster communication between servers and clients.
---

# `tls` Block

<Placement groups={['tls']} />

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.

```hcl
tls {
  http = true
  rpc  = true
}
```

~> Incorrect configuration of the TLS configuration can result in failure to
start the Nomad agent.

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](/nomad/tutorials/transport-security/security-enable-tls).

## `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`](#verify_https_client), 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][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.

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

- `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`](#http) 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.

```hcl
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.

[raft]: https://github.com/hashicorp/serf 'Serf by HashiCorp'
