Secure gossip communication with encryption

9min
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Consul

There are two different systems that need to be configured separately to encrypt communication within the datacenter: gossip encryption and TLS. TLS is used to secure the RPC calls between agents. Gossip communication is secured with a symmetric key, since gossip between agents is done over UDP. In this tutorial, you will only configure gossip encryption.

Gossip encryption

To enable gossip encryption, you need to use an encryption key when starting the Consul agent. The key can be set with the encrypt parameter in the agent configuration file. Alternatively, the encryption key can be placed in a separate configuration file with only the encrypt field, since the agent can merge multiple configuration files. The key must be 32-bytes, Base64 encoded.

You can use the Consul CLI command, consul keygen, to generate a cryptographically suitable key.

$ consul keygen
p1c6tzMpKFBA5TcHaCzJWMxxU4dTreuxBGhRE/iocA8=

Enable on a new Consul datacenter

To enable gossip on a new datacenter, you will add the encryption key parameter to the agent configuration file and then pass the file at startup with the -config-dir flag.

/etc/consul.d/consul.hcl

12345data_dir = "/opt/consul"
log_level = "INFO"
node_name = "bulldog"
server = true
encrypt = "p1c6tzMpKFBA5TcHaCzJWMxxU4dTreuxBGhRE/iocA8="

$ consul agent -config-dir=/etc/consul.d/
==> Starting Consul agent...
           Version: '1.8.1+ent'
           Node ID: 'b5b5a237-458d-c9eb-b301-db1445e50b80'
         Node name: 'bulldog'
        Datacenter: 'dc1' (Segment: '<all>')
            Server: true (Bootstrap: false)
       Client Addr: [127.0.0.1] (HTTP: 8500, HTTPS: -1, gRPC: 8502, DNS: 8600)
      Cluster Addr: 127.0.0.1 (LAN: 8301, WAN: 8302)
           Encrypt: Gossip: true, TLS-Outgoing: false, TLS-Incoming: false, Auto-Encrypt-TLS: false
...

"Encrypt: true" will be included in the output, if encryption is properly configured.

Note: all nodes within the same datacenter must share the same encryption key in order to send and receive datacenter information, including clients and servers. Additionally, if you're using multiple WAN joined datacenters, be sure to use the same encryption key in all datacenters.

Enable on an existing Consul datacenter

Gossip encryption can also be enabled on existing datacenters, but requires several extra steps. The additional configuration of the agent configuration parameters, encrypt_verify_incoming and encrypt_verify_outgoing is necessary.

Step 1: Generate an encryption key using consul keygen.

$ consul keygen
BYX6EPaUiUI0TDdm6gAMmmLnpJSwePJ33Xwh6rjCYbg=

Step 2: Set the encrypt key, and set encrypt_verify_incoming and encrypt_verify_outgoing to false in the agent configuration file. Then initiate a rolling update of all the agents with these new values. After this step, the agents will be able to decrypt gossip but will not yet be able to send encrypted traffic.

/etc/consul.d/consul.hcl

1234567data_dir = "/opt/consul"
log_level = "INFO"
node_name = "bulldog"
server = true
encrypt = "BYX6EPaUiUI0TDdm6gAMmmLnpJSwePJ33Xwh6rjCYbg="
encrypt_verify_incoming = false
encrypt_verify_outgoing = false

A rolling update can be made by restarting the Consul agents (clients and servers) in turn. consul reload or kill -HUP <process_id> is not sufficient to change the gossip configuration.

Step 3: Update the encrypt_verify_outgoing setting to true and perform another rolling update of all the agents by restarting Consul on each agent. The agents will now be sending encrypted gossip but will still allow incoming unencrypted traffic.

/etc/consul.d/consul.hcl

1234567data_dir = "/opt/consul"
log_level = "INFO"
node_name = "bulldog"
server = true
encrypt = "BYX6EPaUiUI0TDdm6gAMmmLnpJSwePJ33Xwh6rjCYbg="
encrypt_verify_incoming = false
encrypt_verify_outgoing = true

Step 4: The previous step, enabling verify outgoing, must be completed on all agents before continuing. Update the encrypt_verify_incoming setting to true and perform a final rolling update on all the agents.

/etc/consul.d/consul.hcl

1234567data_dir = "/opt/consul"
log_level = "INFO"
node_name = "bulldog"
server = true,
encrypt = "BYX6EPaUiUI0TDdm6gAMmmLnpJSwePJ33Xwh6rjCYbg=",
encrypt_verify_incoming = true,
encrypt_verify_outgoing = true

All the agents will now be strictly enforcing encrypted gossip. Note, the default behavior of both encrypt_verify_incoming and encrypt_verify_outgoing is true. You have set them in the configuration file as an explicit example.

Next steps

In this tutorial, you configured gossip encryption for all agents in your Consul datacenter. Complete the Secure Agent Communication with TLS Encryption tutorial and Secure Consul with Access Control Lists (ACLs) to finish securing your Consul datacenter.

Collection Overview

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TLS encryption