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Cluster Security

EMQX provides several security mechanisms to ensure the confidentiality, integrity, and availability of data, including authentication and authorization mechanisms on the node level, a secret cookie to ensure secure communication between nodes in a cluster, and TLS/SSL encryption to provide end-to-end encryption for inter-node traffic.

To help provision firewall rules, we will also touch on EMQX's inter-broker communication port mapping rules.

For security concerns, you should change the default cookie settings to a Secret cookie in emqx.conf on all nodes to join the cluster.

Note: All nodes to join the cluster should use the same Secret cookie. For details about the magic cookie used, see Distributed Erlang - Security.

node {
  cookie = "<a Secret cookie>"


All nodes to join the cluster should use the same security cookie. For details about the magic cookie used, see Distributed Erlang - Security.

Configure TLS/SSL to Secure Cluster Connections

EMQX also supports using TLS to secure the communication channel between EMQX nodes to protect the confidentiality, integrity, and authenticity of the data exchanged between them. TLS comes at the cost of increased CPU load and RAM usage, please configure as per your business needs.

This section introduces how to configure TLS for EMQX clusters. On how to obtain an SSL/TLS certificate, see Enable SSL/TLS Connection.

Use TLS/SSL for Cluster RPC Connections

To configure TLS/SSL for cluster RPC below configuration items should be set in emqx.conf.

rpc {
  driver = ssl
  # PEM format file containing the trusted CA (certificate authority) certificates that the listener uses to verify the authenticity of the cluster peers.
  cacertfile = "/path/to/cert/ca.pem"
  # PEM format 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.
  certfile = "/path/to/cert/domain.pem"
  # PEM format file containing the private key corresponding to the SSL/TLS certificate
  keyfile = "/path/to/cert/domain.key"
  # Set to 'verify_peer' to verify the authenticity of the clients' certificates, otherwise 'verify_none'.
  verify = verify_peer
  # If set to true, the handshake fails if the peer does not have a certificate to send, that is, sends an empty certificate. If set to false, it fails only if the peer sends an invalid certificate (an empty certificate is considered valid).
  fail_if_no_peer_cert = true

Use TLS/SSL for Erlang Distribution

EMQX core nodes use Erlang distribution to synchronize database updates and manage nodes in the cluster, such as starting/stopping a component or collecting runtime metrics, etc.

  • Make sure to verify etc/ssl_dist.conf file has the right paths to keys and certificates.
  • Ensure config cluster.proto_dist is set to inet_tls.

Port Mapping

It's a good practice to keep the clustering ports internal by configuring firewall rules e.g., AWS security groups or iptables. If there is a firewall between the cluster nodes, the conventional listening ports should be allowed for other nodes in the cluster to reach. This section introduces the port mapping rules, which ensure that the firewall rules are configured correctly, allowing EMQX nodes to connect to each other while preventing unauthorized access from external sources.

EMQX uses a port mapping rule for clustering to ensure that the communication between nodes is reliable and efficient. EMQX nodes communicate with each other through two different channels, Erlang Distribution ports and Cluster RPC ports.

ChannelDescriptionDefault Port
Erlang Distribution PortsFor node communications4370
Cluster RPC PortsFor node administrative tasks, such as node joining or leaving5370 or
5369 if EMQX is deployed via Docker

EMQX applies the same port mapping rule for Erlang Distribution Ports and Cluster RPC Ports, which is:

ListeningPort = BasePort + Offset

The offset is calculated based on the numeric suffix of the node's name. If the node's name does not have a numeric suffix, then the offset is set to 0. For example:

  • For node emqx@, it does not have a numeric suffix, the port will be 4370 for Erlang Distribution Ports (or 5370 for Cluster RPC Ports).
  • For node emqx1@, the numeric suffix is 1, the port will be 4371 (or 5371 for Cluster RPC Ports).