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Configuration Files

Users can configure EMQX with configuration files or environment variables. This chapter will introduce the EMQX configuration files. For configuration items and detailed introduction, see Configuration Manual.

Configuration Files

Main Configuration File

EMQX will create a group of directories after installation, among which, etc is the folder that keeps all the configuration files. This section will focus on the main configuration file: emqx.conf.

Depends on your installation mode, emqx.conf is stored in:

Installed with RPM or DEB package/etc/emqx/emqx.conf
Running in docker container/opt/emqx/etc/emqx.conf
Extracted from portable compressed package./etc/emqx.conf

As the main configuration file, emqx.conf contains most of the commonly used configuration items. You can follow the example provided in the emqx.conf.example file (located within the same directory) to customize the settings. EMQX uses the default settings if a config item is not found in the config files.

Configuration Rewrite File

emqx.conf defines settings at a global level, for cases where you need to customize the settings for a cluster or a node, EMQX also provides a configuration rewrite file which extends but does not override emqx.conf:


Contains configuration items for the entire cluster, configuration changes made from Dashboard, REST API, and CLI will be persisted to this file.

If a certain cluster node is restarted or some new nodes are added, the node will automatically copy and apply the configuration file from other nodes within the cluster, therefore there is no need nor recommended to configure it manually.

The configuration rewrite files are located in the $data/configs/ directory, and the path of the data directory varies according to the installation method:

Installed with RPM or DEB package/var/lib/emqx
Running in docker container/opt/emqx/data
Extracted from portable compressed package./data


It is possible to change data directory from config node.data_dir or environment variable EMQX_NODE__DATA_DIR, however, when running a cluster, all nodes should have the same path.

By default, most global settings are defined in the emqx.conf file, if you perform certain operations on the cluster level from Dashboard, REST API or CLI, the changes will be stored in cluster.hocon. And this whole process is called hot reload.

For override rules, see Configure override rules.


Some configuration items cannot be overridden, for example,

Since version 5.1, when cluster configuration changes, EMQX backups the cluster.hocon file before overwriting it. The backup files are suffixed with a timestamp of the node's local time. At most 10 backup files can be kept.

HOCON Configuration Format

Since EMQX 5.0, we have begun to use Human-Optimized Config Object Notation (HOCON) as the configuration file format.

HOCON is a format for human-readable data and a superset of JSON. With features like inheritance, combined, and quotes, HOCON further simplifies the configuration work.

HOCON syntax:

HOCON values can be represented as JSON-like objects, for example:

node {
  name = "emqx@"
  cookie = "mysecret"
  cluster_call {
    retry_interval  =  1m

or in flattening:

bash = ""
node.cookie = "mysecret"
node.cluster_call.retry_interval = "1m"

This cuttlefish-like flattening format is backward compatible with the previous EMQX versions, but it is used differently:

HOCON recommends adding quotes at both ends of the string. Strings without special characters can also be unquoted, for example foo, foo_bar, while cuttlefish regards all characters to the right of = as values.

For more information about HOCON syntax, please refer to HOCON Documentation.

Environment Variables

Besides configuration files, you can also use environment variables to configure EMQX.

For example, environment variable EMQX_NODE__NAME=emqx2@ will override the following configuration:

# emqx.conf
node {
  name = "emqx@"

Configuration items and environment variables can be converted by the following rules:

  1. Since the . separator in the configuration file cannot be used in environment variables, EMQX uses double underscores __ as the configuration separator;
  2. To distinguish the converted configuration items from other environment variables, EMQX also adds a prefix EMQX_ to the environment variable;
  3. The value of the environment variable is parsed according to the HOCON value, making it possible to use the environment variable to pass the value of complex data types, but please note that special characters such as and = need to be wrapped in double quotes ".

Conversion example:

# Environment variables

## localhost:1883 will be parsed into a struct `{"localhost": 1883}`, so it needs to be wrapped in double quotes

## Pass the HOCON array directly by character

# Configuration file
listeners.ssl.default {
    bind = ""
    ssl_options {
      ciphers = ["TLS_AES_256_GCM_SHA384"]


EMQX will ignore undefined root paths, for example, EMQX_UNKNOWN_ROOT__FOOBAR , because UNKNOWN_ROOT is not a pre-defined root path.

When a known root path is set with an unknown field name, EMQX will output a warning log at startup, for example, when enable is incorrectly configured as enabled, it will output:

[warning] unknown_env_vars: ["EMQX_AUTHENTICATION__ENABLED"]

Configure Override Rules

The value of HOCON will be overridden hierarchically, the rules are as follows:

  • In the same file, the value defined in the later section will override any previous key value.
  • A higher-level value will replace that of a lower-level.

The EMQX configuration is prioritized (overlayed) in the following order: cluster.hocon < emqx.conf < environment variables.

Settings in environment variables that begin with 'EMQX_' have the highest priority and will override any settings in the etc/emqx.conf file.

Changes made through EMQX Dashboard UI, HTTP API, or CLI are persisted in data/configs/cluster.hocon at runtime and will take effect immediately. However, if the same configuration items are set differently in the etc/emqx.conf file, the runtime updates will be overridden by the settings in etc/emqx.conf after the node restarts.

To avoid confusion, it is highly recommend NOT to have the same config keys in both cluster.hocon and emqx.conf.


  1. If you're using an older version of EMQX, specifically version e5.0.2/v5.0.22 or earlier(i.e. the cluster-override.conf file still exists in EMQX's data directory), then the order of priority for configuring your settings is as follows: emqx.conf < ENV < HTTP API(cluster-override.conf).
  2. If you're upgrading from e5.0.2/v5.0.22 or earlier to the latest version of EMQX, the configuration overriding order will remain unchanged, cluster.hocon will not be created to keep compatibility.
  3. The cluster-override.conf mechanism is scheduled to be removed in version 5.1.


In the following configuration, the debug value of level defined in the last line will overwrite the previously defined error, but the enable field remains unchanged:

log {
    enable = true
    level = error

## Set the console log printing level to debug, and keep the other configurations
log.console_handler.level = debug

The packet size limit was first set to 1MB, then overridden to 10MB:

zone {
  zone1 {
    mqtt.max_packet_size = 1M
zone.zone1.mqtt.max_packet_size = 10M

List Element Override

EMQX array has two expression ways:

  • List, for example, [1, 2, 3]
  • Map (subscribing), for example: {"1"=1, "2"=2, "3"=3}

The following 3 formats are equivalent:

authentication.1 = {...}
authentication = {"1": {...}}
authentication = [{...}]

Based on this feature, we can easily override the value of an element in an array, for example:

authentication  = [
    enable = true,
    backend = "built_in_database",
    mechanism = "password_based"

# The `enable` field of the first element can be overridden in the following way:
authentication.1.enable = false


Arrays (in list format) will be fully overwritten and original value cannot be kept, for example:

authentication = [
    enable = true
    backend = "built_in_database"

## With the following method, all fields except `enable` of the first element will be lost.
authentication = [{ enable = true }]


To make the HOCON objects type-safe, EMQX introduced a schema for it. The schema defines data types, and data fields' names and metadata for config value validation and more.


The configuration document you are reading now is generated from schema metadata.

Primitive Data Types

Complex types define data 'boxes' which may contain other complex data or primitive values. There are quite some different primitive types, to name a few:

  • atom().
  • boolean().
  • string().
  • integer().
  • float().
  • number().
  • binary(), another format of string().
  • emqx_schema:duration(), time duration, another format of integer()
  • ...


The primitive types are mostly self-describing, so there is usually not a lot to document. For types that are not so clear by their names, the field description is to be used to find the details.

Complex Data Types

There are 4 complex data types in EMQX's HOCON config:

  1. Struct: Named using an unquoted string, followed by a predefined list of fields. Only lowercase letters and digits are allowed in struct and field names. Also, only underscore can be used as a word separator.
  2. Map: Map is like Struct, however, the fields are not predefined.
  3. Union: MemberType1 | MemberType2 | ...
  4. Array: [ElementType]


If map filed name is a positive integer number, it is interpreted as an alternative representation of an Array. For example:

myarray.1 = 74
myarray.2 = 75

will be interpreted as myarray = [74, 75], which is handy when trying to override array elements.

Configuration Paths

If we consider the whole EMQX config as a tree, to reference a primitive value, we can use dot-separated names from string for the path from the tree root (always a Struct) down to the primitive values at tree-leaves.

Each segment of the dotted string is a Struct filed name or Map key. For Array elements, 1-based index is used.

Below are some examples

bash = "emqx."
zone.zone1.max_packet_size = "10M"
authentication.1.enable = true