# Migrate from V4

This section provides guidelines for migrating from EMQX 4.x to 5.0. EMQX 5.0 is not backward compatible with 4.x in management APIs and clustering APIs. However, most of the functionality is not significantly changed.

# Log

Compared with 4.x, the most significant change in the log is the format. In 4.x, the log text is primarily plain, aiming for good human readability. However, starting from 5.0, we moved to structured logging without losing readability. For instance, most log fields use underscores as word separators, making them more search-friendly. This format also helps log indexing tools to index the logs more effectively.

2022-06-29T16:58:53.235042+02:00 [info] foo: bar, msg: msg_for_human_to_read_but_also_easy_to_index

Find more details in Log & Trace.

# Default listeners

By default, the following listeners are no longer provided:

Listeners	Description
MQTT-TCP 11883	Listeners for backend applications
Management-HTTP 8081	For REST API, merged to port 18083

# Plugins

The previous official plugins have been migrated to EMQX as built-in functions. Custom plugins developed for version 4.x need to be adapted before they can be used in EMQX 5.0. The following is a comparison table between official plugins and existing functions:

4.x	5.0
emqx_auth_http	AuthN/AuthZ - HTTP data source
emqx_auth_jwt	AuthN/AuthZ - JWT
emqx_auth_mnesia	AuthN/AuthZ - Built-in database
emqx_auth_mongo	AuthN/AuthZ - MongoDB data source
emqx_auth_mysql	AuthN/AuthZ - MySQL data source
emqx_auth_pgsql	AuthN/AuthZ - PostgreSQL data source
emqx_auth_redis	AuthN/AuthZ - Redis data source
emqx_sasl	AuthN/AuthZ - MQTT 5 Enhanced Authentication
emqx_auth_ldap	-
emqx_rule_engine	Data Integration
emqx_bridge_mqtt	Data Bridge - MQTT Sink/MQTT Source
emqx_web_hook	Data Bridge - WebHook
emqx_coap	CoAP Gateway
emqx_dashboard	Dasboard
emqx_exhook	ExHook
emqx_exproto	ExProto Gateway
emqx_lwm2m	LwM2M Gateway
emqx_sn	MQTT-SN Gateway
emqx_stomp	STOMP Gateway
emqx_lua_hook	-
emqx_management	-
emqx_prometheus	Prometheus
emqx_psk_file	AuthN - PSK (`psk_authentication.enable = true`)
emqx_recon	Old features still available from CLI `emqx_ctl observer`
emqx_retainer	Retain
emqx_telemetry	Telemetry

# HTTP API

Previously, "Applications" dashboard section was used to manage API access credentials. Now "API Key" section should be used to create credentials. The credentials consist of API Key and Secret Key that can be respectively used as username and password in HTTP basic auth. Secret Key is only displayed once when credentials are created, but cannot be obtained again later.

Port 8081 has been merged into port 18083, and the basic path of API access has been switched from /api/v4 to /api/v5. Call the API through port 18083 and path /api/v5.

String timestamps are now in RFC3339 (opens new window) format.

# Data Format Changes

When the response is successful, the business status code code will no longer be returned with the data, and the corresponding 4xx/5xx HTTP status code and error prompt will be returned when an error occurs. Users can access GET /error_codes to get all possible error codes. The following is a comparative example of the response format:

# 4.x successful response
## HTTP StatusCode = 200
GET /api/v4/rules/my_rule
{ "code": 0, "data": { ... } }

# 4.x error response
## HTTP StatusCode = 200
GET /api/v4/rules/my_rule
{ "code": 404, "message": "Not Found" }

# 5.0 successful response
## HTTP StatusCode = 200
GET /api/v5/rules/my_rule
{ ... }

# 5.0 error response
## HTTP StatusCode = 404
GET /api/v5/rules/my_rule
{ "code": "NOT_FOUND", "message": "Rule Id Not Found" }

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# Major API Changes

The API has undergone significant changes, and some APIs have been made compatible. The following is a comparison table of commonly used API changes.

TIP

Compatibility Notes:

Compatible: Use the old API path and parameters, or keep the old API.
Partially compatible: The API path remains unchanged, but some API fields have changed.
Incompatible: API paths and fields have changed.

4.x	5.0	Compatibility	Notes
Publish/Subscribe
`POST /mqtt/publish`	`POST /publish`	Compatible
`POST /mqtt/publish_batch`	`POST /publish/bulk`	Compatible
`POST /mqtt/subscribe`	`POST /clients/{clientid}/subscribe`	Compatible
`POST /mqtt/subscribe_batch`	`POST /clients/{clientid}/subscribe/bulk`	Compatible
`POST /mqtt/unsubscribe`	`POST /clients/{clientid}/unsubscribe`	Compatible
`POST /mqtt/unsubscribe_batch`	`POST /clients/{clientid}/unsubscribe/bulk`	Compatible
Clients/Topics/Subscriptions
`GET /clients`	`GET /clients`	Partially compatible
`GET /routes{/topic}`	`GET /topics{/topic}`	Incompatible	`routes` renamed to `topics`
`GET /subscriptions`	`GET /subscriptions`	Partially compatible
`GET /subscriptions/{clientid}`	`GET /clients/{clientid}/subscriptions`	Incompatible
Node/Stats/Metrics
`GET /nodes`	`GET /nodes`	Partially compatible
`GET /brokers`	-	Incompatible	merged to `GET /nodes`
`GET /stats`	`GET /stats`	Partially compatible
`GET /metrics`	`GET /metrics`	Partially compatible
Users/Alarms
`GET /users`	`GET /users`	Partially compatible
`GET /alarms{/activated}`	`GET /alarms?activated={true,false}`	Incompatible
`GET /alarms{/deactivated}`	`GET /alarms?activated={true,false}`	Incompatible

# Auth/ACL

The Auth and ACL plugins (emqx_auth_*) have been removed, and the corresponding functions are built into EMQX. Users can configure them through Dashboard or configuration files.

Auth is renamed to Authentication, and ACL is renamed Authorization. Now they are independent of each other.

Version 5.0 supports the authentication methods and most data sources in 4.x, but there are certain adjustments in the usage.

# Fixed Order of Execution

When multiple authenticators or authorization checkers are enabled simultaneously, the checks are no longer performed according to the startup order but a fixed configuration order. The execution order can be adjusted in the configuration file and Dashboard.

# Variable Interpolation Syntax

Previously, the Auth plugins could use %u syntax to construct variable placeholders, dynamically interpolating client information into SQL statements, Redis query commands, and HTTP requests. Now EMQX uses the new syntax ${}, such as ${username}, ${clientid}, which is consistent with the rule SQL.

Usage example:

# 4.x
# etc/emqx_auth_mysql.conf
auth.mysql.auth_query = select password from mqtt_user where username = '%u' limit 1

# 5.0
# emqx.conf
authentication = [
  {
    ...
    mechanism = "password_based"
    backend = "mysql"
    query = "SELECT password_hash, salt FROM mqtt_user where username = ${username} LIMIT 1"
  }
]

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# Auth

# Remove the Anonymous Mechanism

Remove the allow_anonymous configuration item. All client connections are allowed by default. If add and enable any authenticator, EMQX will perform an authentication check for all new connections.

Remove the bypass_auth_plugins configuration item. When a listener needs to disable authentication, it can be set through the listeners.{type}.{name}.enable_authn = true | false configuration item.

# Built-in database (Mnesia)

Mnesia is renamed to the built-in database;
Only two search methods are available: username-based or clientid-based;
The data format and REST API have changed. For more information, refer to POST /authentication/{id}/users.

Users can use the data import API to import data from older versions into EMQX 5.0, see POST /authentication/{id}/import_users for details.

# HTTP

Use the JSON fields inside the response body instead of the HTTP response status codes to identify the authentication result;
Remove the super user query configuration. If you need the super-user function, set it through JSON in the response body of successful authentication.

Success response status code:

200 or 204

The authenticator will be ignored if the request fails or returns another status code.

Success Response Body (JSON):

Name	Type	Required	Description
result	Enum	true	`allow \| deny \| ignore`
is_supseruser	Boolean	false

{
  "result": "allow",
  "is_supseruser": true
}

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# MySQL/PostgreSQL

The password field required in the query result is changed from password to password_hash. If you do not want to change the database column name, you can use as to complete the migration;
Remove the super-user query SQL. If you need to give clients super-user permissions, please ensure that the authentication SQL result contains the is_superuser field.

SELECT password as password_hash, salt, is_superuser FROM mqtt_user where username = ${username} LIMIT 1

# MongoDB

Remove the super-user query. If you need to give clients super-user permissions, specify the is_superuser_field field.

authentication = [
  {
    ...
    mechanism = "password_based"
    backend = "mongodb"
    # is_superuser_field = "is_superuser"
  }
]

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# Redis

Only supports Redis Hashes (opens new window) data structure and HGET, HMGET query commands. The commands must return password_hash as the password field name;
Remove the super-user query. If you need to give clients super-user permissions, please add the is_superuser field to the Redis query command.

# bad
GET emqx_user:${username}
# bad
HMGET emqx_user:${username} passwd

# good
HMGET emqx_user:${username} password_hash

# good
HMGET emqx_user:${username} password_hash is_superuser

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# LDAP

Not supported for now.

# JWT

No changes.

# Authorization (ACL)

# ACL File

Remove the acl_file configuration. The file-based ACL (acl.conf) will be used as one of the authorization sources and added to EMQX by default;
The acl.conf file is moved from the etc directory to the data/authz directory. Please ensure that EMQX has read and write permissions for this file;
acl.conf data file syntax has changed

4.x	5.0.0	Compatibility
user	username	Yes
client	clientid	Yes
pubsub	all	No

# Built-in Database (Mnesia)

Mnesia renamed to the built-in database;
The data format and REST API have changed. For more information, please refer to POST /authorization/built_in_database/clientid.

4.x ACL data can be exported with ./bin/emqx_ctl data export command. Users may convert the data into 5.0 format and import it through the corresponding REST API.

# MySQL/PostgreSQL

The ipaddr/username/clientid field is no longer required in the query result;
The access field name is changed to action, and its data type is changed from integer to character or character enumeration.
The allow field name is changed to permission, and its data type is changed from integer to character or character enumeration.

The correspondence between 4.x integer values and 5.0 character/enumeration values is shown in the following tables.

access/action field mapping

4.x (int)	5.0.0 (varchar/enum)	action
1	subscribe	subscribe
2	publish	publish
3	all	subscribe & publish

allow/permission field mapping

4.x (int)	5.0.0 (varchar/enum)	permission
0	deny	deny
1	allow	allow

# MongoDB

MongoDB data source can be used for both allow and deny rules. Previously, only white list mode was supported, and it was required to set acl_nomatch = deny;
You need to select documents containing the action, permission and topics fields from MongoDB. For details, see AuthZ-MongoDB.

If you want to continue using the data from in 4.x, please make necessary migrations manually.

Data example in 5.0

[
  {
      "username": "emqx_u",
      "clientid": "emqx_c",
      "ipaddress": "127.0.0.1",
      "permission": "allow",
      "action": "all",
      "topics": ["#"]
  }
]

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# Redis

Redis data source still only supports white list mode, which requires setting acl_nomatch = deny;
The access field name changes to action, and the data changes from numbers to action strings. The correspondence is shown in the table below.

4.x	5.0.0	action
1	subscribe	subscribe
2	publish	publish
3	all	subscribe & publish

If you want to continue using the data from in 4.x, please make necessary migrations manually.

Data example in 5.0

HSET mqtt_acl:emqx_u t/# subscribe
HSET mqtt_acl:emqx_u # all
HSET mqtt_acl:emqx_u a/1 publish

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# HTTP

Use the JSON fields in the response body instead of the HTTP response status codes to identify the authentication result.

Success response status code:

200 or 204

Other status codes or request failure will be treated as ignore.

Success Response Body (JSON):

Name	Type	Required	Description
result	Enum	true	`allow \| deny \| ignore`

{
  "result": "deny"
}

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# Rule Engine

Rule SQL is fully compatible with 4.x syntax, but the actions under the rule are split into built-in actions (republish, console) and data bridges (WebHook, MQTT Sink, MQTT Source) to provide reuse of actions.

# WebHook

The WebHook plugin (emqx_web_hook) has been removed. Use the WebHook data bridge in Data Integration instead.

# MQTT Bridge

The MQTT bridge plugin (emqx_bridge_mqtt) has been removed. Use the MQTT Sink and MQTT Source data bridge in Data Integration instead.

# Prometheus

Prometheus scraping endpoint is enabled by default, and no authentication is required to scrap the metrics.

You can use curl command to inspect the metrics: curl -f "127.0.0.1:18083/api/v5/prometheus/stats"

If you want to enable push-gateway, configure it in the dashboard or through prometheus {...} config block.

Changes:

4.4.4	5.0	Description
emqx_client_auth_success_anonymous	emqx_client_auth_anonymous	Renamed
emqx_client_check_acl	emqx_client_authorize counter	Renamed
-	emqx_mria_last_intercepted_trans	New
-	emqx_mria_replicants	New
-	emqx_mria_server_mql	New
-	emqx_mria_weight	New
emqx_routes_count	emqx_topics_count	Renamed
emqx_routes_max	emqx_topics_max	Renamed
emqx_session_takeovered	emqx_session_takenover	Renamed
erlang_vm_ets_tables	-	Removed
-	erlang_vm_memory_dets_tables	New
-	erlang_vm_memory_ets_tables	New
-	erlang_vm_msacc_alloc_seconds_total	New
-	erlang_vm_msacc_aux_seconds_total	New
-	erlang_vm_msacc_bif_seconds_total	New
-	erlang_vm_msacc_busy_wait_seconds_total	New
-	erlang_vm_msacc_check_io_seconds_total	New
-	erlang_vm_msacc_emulator_seconds_total	New
-	erlang_vm_msacc_ets_seconds_total	New
-	erlang_vm_msacc_gc_full_seconds_total	New
-	erlang_vm_msacc_gc_seconds_total	New
-	erlang_vm_msacc_nif_seconds_total	New
-	erlang_vm_msacc_other_seconds_total	New
-	erlang_vm_msacc_port_seconds_total	New
-	erlang_vm_msacc_send_seconds_total	New
-	erlang_vm_msacc_sleep_seconds_total	New
-	erlang_vm_msacc_timers_seconds_total	New
-	erlang_vm_statistics_dirty_cpu_run_queue_length	New
-	erlang_vm_statistics_dirty_io_run_queue_length	New
-	erlang_vm_wordsize_bytes	New

# Gateway/Multi-Protocol Support

Clients of other protocols than MQTT (LwM2M, CoAP, STOMP, MQTT-SN) are no longer listed as MQTT clients on the dashboard Connections page and in the GET /clients API. They can be found in Extentions -> Gateways section or listed with GET /gateway/{name}/clients API.

# Telemetry

The telemetry plugin (emqx_telemetry) has been removed, please configure it through the telemetry {} configuration item or in the Dashboard System Settings -> Settings page.

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