Cluster Configuration

In EMQX, a cluster is a group of EMQX nodes that work together to provide a highly scalable and fault-tolerant MQTT messaging system. Clustering allows you to distribute the load across multiple nodes and ensure that the system can continue to operate even if one or more nodes fail.

Configure Node Names

Before starting the cluster creation step, let's first get familiar with the concept of node names in EMQX. EMQX nodes are identified by their names. A node name consists of two parts, node name and host, separated with @, for example, emqx@s1.emqx.io. The host part must either be the IP address or a fully qualified domain name (FQDN), such as myhost.example.tld, for instance:

• For the EMQX node deployed on server s1.emqx.io, the node name should be emqx@s1.emqx.io;
• If this server has a static IP (192.168.0.10), the node name should be emqx@192.168.0.10.

When configuring nodes with emqx.conf, you can work with the code below:

node {
  name = "emqx@s1.emqx.io"
  role = core
}

Where,

• name refers to the desired node name, for example, emqx@localhost.
• role refers to the function that an EMQX node performs within an EMQX cluster. There are 2 types of roles: core nodes and replicant codes. For a detailed explanation of core nodes and replicant nodes, see EMQX Clustering - Core and Replicant Nodes.
  • Default value: core
  • Optional value: core or replicant

Configure Cluster

This section introduces how to configure an EMQX cluster. You can add the cluster configuration items either on a core or replicant node. If you are working on a replicant node, there are some configuration items, for example, core_nodes, that only take effect under certain preconditions:

• node.db_backend of the node is set to rlog, indicating the node uses rlog as the database backend.
• node.role is set to replicant, indicating this code functions as a replicant node.
• node.discovery_strategy is set to manual or static, there is no need to set this configuration item if automatic cluster discovery mechanism is used. For a detailed explanation of the node discovery strategy and the corresponding configuration items, see Create Cluster.

cluster {
  name = emqxcl
  discovery_strategy = manual
  core_nodes = []
  driver = tcp
  ssl_options {
    certfile = ""
    keyfile = ""
    cacertfile = ""
  }
}

Where,

Configuration Item	Description	Default Value	Optional Values
name	This sets the name of the cluster	emqxcl
discovery_strategy	This sets the node discovery strategy for the cluster.	manual	manual, static, DNS, etcd, k8s
core_nodes	This sets the core nodes that this replicant code will connect to. Multiple nodes can be added here, separated with a ,	--	--
driver	This sets the transport protocol for inter-EMQX node communication.	tcp	tcp, SSL
ssl_options	This sets the SSL/TLS configuration options for the listener, it has three properties	--	--
ssl_options.cacertfile	PEM file containing the trusted CA (certificate authority) certificates that the listener uses to verify the authenticity of the client certificates.	--	--
ssl_options.certfile	PEM file containing the SSL/TLS certificate chain for the listener. If the certificate is not directly issued by a root CA, the intermediate CA certificates should be appended after the listener certificate to form a chain.	--	--
ssl_options.keyfile	PEM file containing the private key corresponding to the SSL/TLS certificate.	--	--
ssl_options.fail_if_no_peer_cert	If set to true, the server fails if the client does not have a certificate to send, that is, sends an empty certificate. If set to false, it fails only if the client sends an invalid certificate (an empty certificate is considered valid).	--	--

EMQX has offered more configuration items to serve customized needs better. For details, see Configuration Manual.