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docs	Gossip and RPC Encryption	docs-agent-encryption	Learn how to configure Nomad to encrypt HTTP, RPC, and Serf traffic.

Encryption

The Nomad agent supports encrypting all of its network traffic. There are two separate encryption systems, one for gossip traffic, and one for HTTP and RPC.

Gossip

Enabling gossip encryption only requires that you set an encryption key when starting the Nomad server. The key can be set via the encrypt parameter: the value of this setting is a server configuration file containing the encryption key.

The key must be 16-bytes, base64 encoded. As a convenience, Nomad provides the nomad keygen command to generate a cryptographically suitable key:

$ nomad keygen
cg8StVXbQJ0gPvMd9o7yrg==

With that key, you can enable gossip encryption on the agent.

HTTP, RPC, and Raft Encryption with TLS

Nomad supports using TLS to verify the authenticity of servers and clients. To enable this, Nomad requires that all clients and servers have key pairs that are generated and signed by a Certificate Authority. This can be a private CA.

TLS can be used to verify the authenticity of the servers and clients. The configuration option verify_server_hostname causes Nomad to verify that a certificate is provided that is signed by the Certificate Authority from the ca_file for TLS connections.

If verify_server_hostname is set, then outgoing connections perform hostname verification. Unlike traditional HTTPS browser validation, all servers must have a certificate valid for server.<region>.nomad or the client will reject the handshake. It is also recommended for the certificate to sign localhost such that the CLI can validate the server name.

TLS is used to secure the RPC calls between agents, but gossip between nodes is done over UDP and is secured using a symmetric key. See above for enabling gossip encryption.

Configuring the command line tool

If you have HTTPS enabled for your Nomad agent, you must export environment variables for the command line tool to also use HTTPS:

# NOMAD_ADDR defaults to http://, so set it to https
# Alternatively you can use the -address flag
export NOMAD_ADDR=https://127.0.0.1:4646

# Set the location of your CA certificate
# Alternatively you can use the -ca-cert flag
export NOMAD_CACERT=/path/to/ca.pem

Run any command except agent with -h to see all environment variables and flags. For example: nomad status -h

By default HTTPS does not validate client certificates, so you do not need to give the command line tool access to any private keys.

Network Isolation with TLS

If you want to isolate Nomad agents on a network with TLS you need to enable both verify_https_client and verify_server_hostname. This will cause agents to require client certificates for all incoming HTTPS connections as well as verify proper names on all other certificates.

Consul will not attempt to health check agents with verify_https_client set as it is unable to use client certificates.

Encryption Examples

TLS Configuration using cfssl

While Vault's PKI backend is an ideal solution for managing certificates and other secrets in a production environment, it's useful to use simpler command line tools when learning how to configure TLS and your PKI.

cfssl is a tool for working with TLS certificates and certificate authorities similar to OpenSSL's x509 command line tool.

Once you have the cfssl command line tool installed, the first step to setting up TLS is to create a Certificate Authority (CA) certificate. The following command will generate a suitable example CA CSR, certificate, and key:

# Run in the directory where you want to store certificates
$ cfssl print-defaults csr | cfssl gencert -initca - | cfssljson -bare ca

Next create a nomad-csr.json which contains the configuration for the actual certificate you'll be using in Nomad:

{
  "CN": "global.nomad",
  "hosts": [
    "server.global.nomad",
    "client.global.nomad",
    "localhost"
  ]
}

This will create a certificate suitable for both clients and servers in the global (default) region.

In production Nomad agents should have a certificate valid for the name ${ROLE}.${REGION}.nomad where role is either client or server depending on the node's role.

Create a certificate signed by your CA:

$ cfssl gencert -ca ca.pem -ca-key ca-key.pem nomad-csr.json | cfssljson -bare nomad

You've now successfully generated self-signed certificates! You should see the following files:

• ca.pem - the CA certificate. This corresponds to the Nomad ca_file parameter in the Nomad tls stanza.

• ca-key.pem - the CA private key. This is used to sign CSRs and should not be included in the Nomad tls stanza.

• nomad.pem - the Nomad certificate for the region. This corresponds to the cert_file parameter in the Nomad tls stanza.

• nomad-key.pem - the Nomad private key. This corresponds to the key_file parameter in the Nomad tls stanza.

• *.csr - the certificate signing request. This is temporary for generating certificates and should not be included in the Nomad tls stanza.

In your Nomad configuration add the tls stanza:

tls {
  http = true
  rpc  = true

  ca_file   = "ca.pem"
  cert_file = "nomad.pem"
  key_file  = "nomad-key.pem"

  verify_server_hostname = true
}