Manage gossip encryption

This topic describes the steps to enable gossip encryption on a Consul datacenter and rotate the gossip encryption key to maintain secure communication between agents.

Workflows

We recommend enabling gossip encryption to all new deployed Consul datacenters. You can also update the agents in an existing datacenter to use gossip encryption.

The workflow to enable gossip encryption changes depending on whether your datacenter has client agents running.

To enable gossip encryption on a new datacenter:

1. Use consul keygen to generate a new gossip encryption key.
2. Create a configuration file that sets the encrypt parameter to the newly generated key.
3. Distribute the configuration file to all agent nodes that are part of the datacenter. Then start the Consul agent on all the nodes.

To enable gossip encryption on an existing datacenter:

1. Use consul keygen to generate a new gossip encryption key.
2. Create a configuration file that sets the encrypt parameter to the newly generated key and sets encrypt_verify_incoming and encrypt_verify_outgoing to false.
3. Distribute the configuration file to all agent nodes that are part of the datacenter. Then perform a rolling restart of all Consul agents.
4. Update the encrypt_verify_outgoing setting to true and perform a rolling restart of all Consul agents.
5. Update the encrypt_verify_incoming setting to true and perform a rolling restart of all Consul agents.

If you have multiple datacenters joined in WAN federation, be sure to use the same encryption key in all datacenters.

Enable gossip encryption on a new datacenter

We recommend enabling gossip encryption on all new Consul datacenters.

Generate a gossip encryption key

First, generate an encryption key on a Consul server. The Consul CLI includes a consul keygen command to generate a key.

$ consul keygen
YwgWlBvicJN17UOYcutXLpJSZsw5aWpLEEWqgK635zA=

You can generate a new gossip key using any method that can create 32 random bytes encoded in base64. For example, you can use openssl or dd to create a key on Linux with one of the following commands:

• openssl rand -base64 32
• dd if=/dev/urandom bs=32 count=1 status=none | base64

Add the key to the agent configuration

Create a configuration that sets encrypt parameter to the newly generated key. You can edit the existing agent configuration, or you can add a file to the configuration directory. For more information, refer to configuring Consul agents.

encrypt = "YwgWlBvicJN17UOYcutXLpJSZsw5aWpLEEWqgK635zA="

{
  "encrypt": "YwgWlBvicJN17UOYcutXLpJSZsw5aWpLEEWqgK635zA="
}

Add the key to all agent configurations

Distribute the gossip key to all the agent nodes that need to be pert of the datacenter. Then start the Consul agent on all the nodes.

When gossip encryption is properly configured, Gossip Encryption: true appears in the Consul logs at startup.

==> Starting Consul agent...
   Version: '1.19.0'
Build Date: '2024-06-12 13:59:10 +0000 UTC'
   Node ID: 'e74b1ade-e932-1707-cdf1-6579b8b2536c'
 Node name: 'consul-server-0'
Datacenter: 'dc1' (Segment: '<all>')
Server: true (Bootstrap: false)
   Client Addr: [127.0.0.1] (HTTP: 8500, HTTPS: 8443, gRPC: -1, gRPC-TLS: 8503, DNS: 53)
  Cluster Addr: 172.19.0.7 (LAN: 8301, WAN: 8302)
 Gossip Encryption: true
  Auto-Encrypt-TLS: true
   ACL Enabled: true
 Reporting Enabled: false
ACL Default Policy: deny
 HTTPS TLS: Verify Incoming: false, Verify Outgoing: true, Min Version: TLSv1_2
  gRPC TLS: Verify Incoming: false, Min Version: TLSv1_2
  Internal RPC TLS: Verify Incoming: true, Verify Outgoing: true (Verify Hostname: true), Min Version: TLSv1_2
## ...

Enable gossip encryption on an existing datacenter

You can also enable gossip encryption on existing Consul datacenters.

Generate a gossip encryption key

First, generate an encryption key on a Consul server. The Consul CLI includes a consul keygen command to generate a key.

$ consul keygen
YwgWlBvicJN17UOYcutXLpJSZsw5aWpLEEWqgK635zA=

Add the key to the agent configuration

Create a configuration that sets the encrypt parameter to the newly generated key and sets the encrypt_verify_incoming and encrypt_verify_outgoing parameters to false. You can edit the existing agent configuration, or you can add a file to the configuration directory. For more information, refer to configuring Consul agents.

encrypt = "YwgWlBvicJN17UOYcutXLpJSZsw5aWpLEEWqgK635zA="
encrypt_verify_incoming = false
encrypt_verify_outgoing = false

{
"encrypt": "YwgWlBvicJN17UOYcutXLpJSZsw5aWpLEEWqgK635zA=",
"encrypt_verify_incoming" : false,
"encrypt_verify_outgoing" : false
}

Add the configuration to all agents

Distribute the configuration to all the agent nodes that need to be part of the datacenter, and then initiate a rolling update that restarts each agent.

You must restart all of the agents. The consul reload and kill -HUP <process_id> commands are not sufficient when changing the gossip configuration.

Update outgoing encryption

The agents can decrypt gossip communication with the encrypt parameter set, but they are not able to send encrypted traffic.

Update the encrypt_verify_outgoing setting to true and then perform another rolling update of all Consul agents. Complete the process on all the nodes before you begin updates to incoming encryption.

encrypt = "YwgWlBvicJN17UOYcutXLpJSZsw5aWpLEEWqgK635zA="
encrypt_verify_incoming = false
encrypt_verify_outgoing = true

{
"encrypt": "YwgWlBvicJN17UOYcutXLpJSZsw5aWpLEEWqgK635zA=",
"encrypt_verify_incoming": false,
"encrypt_verify_outgoing": true
}

Update incoming encryption

The agents can send encrypted gossip but still allow unencrypted incoming traffic. Update the encrypt_verify_incoming setting to true and then perform a final rolling update on all the agents.

encrypt = "YwgWlBvicJN17UOYcutXLpJSZsw5aWpLEEWqgK635zA="
encrypt_verify_incoming = true
encrypt_verify_outgoing = true

{
"encrypt": "YwgWlBvicJN17UOYcutXLpJSZsw5aWpLEEWqgK635zA=",
"encrypt_verify_incoming": true,
"encrypt_verify_outgoing": true
}

Rotate the gossip encryption key

It is important to periodically rotate the gossip encryption key your Consul datacenter uses.

The process of rotating the gossip encryption key is centralized so that you can perform it on a single datacenter node.

The process to rotate a gossip encryption key consists of the following steps:

1. Generate a new encryption key using the consul keygen command.
2. Install the new encryption key using the consul keyring -install command.
3. Verify the new key is installed in your Consul datacenter with the consul keyring -list command.
4. Instruct Consul to use the new key with the consul keyring -use command.
5. Remove the old key using the consul keyring -remove command.

Generate a new encryption key

Generate a new key using consul keygen:

$ consul keygen
FfRV9j6NXU9LlCI4zLZjjpZdj4Nrqsdm7R8YgzSHzHw=

Add new key to the keyring

Add your newly generated key to the keyring.

$ consul keyring -install FfRV9j6NXU9LlCI4zLZjjpZdj4Nrqsdm7R8YgzSHzHw=
==> Installing new gossip encryption key...

Verify that the new key is installed

After you add the key to one of the Consul agents, Consul propagates it across the entire datacenter. You do not need to repeat the command on other agents.

To ensure that the key has been propagated to all agents, list the installed encryption keys and verify that the number of agents that recognize the key is equal to the total number of agents in the datacenter.

$ consul keyring -list
==> Gathering installed encryption keys...

WAN:
  FfRV9j6NXU9LlCI4zLZjjpZdj4Nrqsdm7R8YgzSHzHw= [1/1]
  YwgWlBvicJN17UOYcutXLpJSZsw5aWpLEEWqgK635zA= [1/1]

dc1 (LAN):
  YwgWlBvicJN17UOYcutXLpJSZsw5aWpLEEWqgK635zA= [7/7]
  FfRV9j6NXU9LlCI4zLZjjpZdj4Nrqsdm7R8YgzSHzHw= [7/7]

Confirm that the two keys are installed in the datacenter and recognized by all agents, including server agents. The server agents are listed in the WAN section. Do not proceed to the next step unless all agents have the new key.

Promote the new key to primary

After all agents recognize the key, it is possible to promote it to be the new primary encryption key.

$ consul keyring -use FfRV9j6NXU9LlCI4zLZjjpZdj4Nrqsdm7R8YgzSHzHw=
==> Changing primary gossip encryption key...

Remove the old key from the keyring

Unused keys in the keyring are a potential security risk to your Consul cluster. We recommended that you remove the former primary key from the keyring after a new key is installed.

$ consul keyring -remove YwgWlBvicJN17UOYcutXLpJSZsw5aWpLEEWqgK635zA=
==> Removing gossip encryption key...

Verify that the keyring contains only one key.

$ consul keyring -list
==> Gathering installed encryption keys...

WAN:
  FfRV9j6NXU9LlCI4zLZjjpZdj4Nrqsdm7R8YgzSHzHw= [1/1]

dc1 (LAN):
  FfRV9j6NXU9LlCI4zLZjjpZdj4Nrqsdm7R8YgzSHzHw= [7/7]

Next steps

Documentation for the commands used in this topic is available at Consul agent configuration - Encryption Parameters. You can find more information over the gossip protocol used by Consul at Gossip Protocol.

After you enable gossip encryption, you can continue to process to secure your Consul datacenter by enabling mutual TLS encryption. For more information, refer to Mutual TLS (mTLS) Encryption.

To learn how to automate gossip key rotation using HashiCorp Vault and consul-template, refer to the Automatically Rotate Gossip Encryption Keys Secured in Vault tutorial.