Maintenance and Monitoring Operations

ACL Replication for Multiple Datacenters

You can configure tokens, policies and roles to work across multiple datacenters. ACL replication has several benefits.

  1. It enables authentication of nodes and services between multiple datacenters.
  2. The secondary datacenter can provide failover for all ACL components created in the primary datacenter.
  3. Sharing policies reduces redundancy for the operator.

Prerequisites

Before starting this guide, each datacenter will need to have ACLs enabled, the process is outlined in the Securing Consul with ACLs guide. This guide includes the additional ACL replication configuration for the Consul agents not covered in the Securing Consul with ACL guide.

Additionally, Basic Federation with WAN Gossip is required.

Introduction

In this guide, you will setup ACL replication. This is a multi-step process that includes:

  • Setting the primary_datacenter parameter on all Consul agents in the primary datacenter.
  • Creating the replication token.
  • Configuring the primary_datacenter parameter on all Consul agents in the secondary datacenter.
  • Enabling token replication on the servers in the secondary datacenter.
  • Applying the replication token to all the servers in the secondary datacenter.

You should complete this guide during the initial ACL bootstrapping process.

Configure the Primary Datacenter

Consul Servers and Clients

You should explicitly set the primary_datacenter parameter on all servers and clients, even though replication is enabled by default on the primary datacenter. Your agent configuration should be similar to the example below.

{
  "datacenter": "primary_dc",
  "primary_datacenter": "primary_dc",
  "acl": {
    "enabled": true,
    "default_policy": "deny",
    "down_policy": "extend-cache",
    "enable_token_persistence": true
  }
}

The primary_datacenter parameter sets the primary datacenter to have authority for all ACL information. It should also be set on clients, so that the they can forward API requests to the servers.

Finally, start the agent.

$ consul agent -config-file=server.json

Complete this process on all agents. If you are configuring ACLs for the first time, you will also need to compelete the bootstrapping process now.

Create the Replication Token for ACL Management

Next, create the replication token for managing ACLs with the following privileges.

  • acl = "write" which will allow you to replicate tokens.
  • operator = "write" for replicating proxy-default configuration entries and enabling CA certificate signing in the secondary datacenter.
  • service_prefix, policy = "read" and intentions = "read" for replicating service-default configuration entries, CA, and intention data.
acl = "write"

operator = "write"

service_prefix "" {
  policy = "read"
  intentions = "read"
}

Now that you have the ACL rules defined, create a policy with those rules.

$ consul acl policy create -name replication -rules @replication-policy.hcl
ID:           240f1d01-6517-78d3-ec32-1d237f92ab58
Name:         replication
Description: Datacenters:
Rules: acl = "write"

operator = "write"

service_prefix "" { policy = "read" intentions = "read" }

Finally, use your newly created policy to create the replication token.

$ consul acl token create description "replication token" -policy-name replication
AccessorID:   67d55dc1-b667-1835-42ab-64658d64a2ff
SecretID:     fc48e84d-3f4d-3646-4b6a-2bff7c4aaffb
Description:  replication token
Local:        false
Create Time:  2019-05-09 18:34:23.288392523 +0000 UTC
Policies:
  240f1d01-6517-78d3-ec32-1d237f92ab58 - replication

Enable ACL Replication on the Secondary Datacenter

Once you have configured the primary datacenter and created the replication token, you can setup the secondary datacenter.

Configure the Servers

You will need to set the primary_datacenter parameter to the name of your primary datacenter and enable_token_replication to true on all the servers.

{
  "datacenter": "dc_secondary",
  "primary_datacenter": "primary_dc",
  "acl": {
    "enabled": true,
    "default_policy": "deny",
    "down_policy": "extend-cache",
    "enable_token_persistence": true,
    "enable_token_replication": true
  }
}

Now you can start the agent.

$ consul agent -config-file=server.json

Repeat this process on all the servers.

Apply the Replication Token to the Servers

Finally, apply the replication token to all the servers using the CLI.

$ consul acl set-agent-token replication <token>
ACL token "replication" set successfully

Once token replication has been enabled, you will also be able to create datacenter local tokens.

Repeat this process on all servers. If you are configuring ACLs for the first time, you will also need to set the agent token.

Note, the clients do not need the replication token.

Configure the Clients

For the clients, you will need to set the primary_datacenter parameter to the name of your primary datacenter and enable_token_replication to true.

{
  "datacenter": "dc_secondary",
  "primary_datacenter": "primary_dc",
  "acl": {
    "enabled": true,
    "default_policy": "deny",
    "down_policy": "extend-cache",
    "enable_token_persistence": true,
    "enable_token_replication": true
  }
}

Now you can start the agent.

$ consul agent -config-file=server.json

Repeat this process on all clients. If you are configuring ACLs for the first time, you will also need to set the agent token.

Check Replication

Now that you have set up ACL replication, you can use the HTTP API to check the configuration.

$ curl http://localhost:8500/v1/acl/replication?pretty
{
  "Enabled":true,
  "Running":true,
  "SourceDatacenter":"primary_dc",
  "ReplicationType":"tokens",
  "ReplicatedIndex":19,
  "ReplicatedTokenIndex":22,
  "LastSuccess":"2019-05-09T18:54:09Z",
  "LastError":"0001-01-01T00:00:00Z"
}

Notice, the "ReplicationType" should be "tokens". This means tokens, policies, and roles are being replicated.

Summary

In this guide you setup token replication on multiple datacenters. You can complete this process on an existing datacenter, with minimal modifications. Mainly, you will need to restart the Consul agent when updating agent configuration with ACL parameters.

If you have not configured other secure features of Consul, certificates and encryption, we recommend doing so now.