emqx4.3/apps/emqx_rule_engine/docs/design.md

EMQX Rule Engine

This is the design guide of message routing rule engine for the EMQX Broker.

Concept

A rule is:

when
    Match <conditions> | <predicates>
then
    Select <data> and Take <action>;

or:

rule "Rule Name"
  when
    rule match
  select
    para1 = val1
    para2 = val2
  then
    action(#{para2 => val1, #para2 => val2})

Architecture

          |-----------------|
   P ---->| Message Routing |----> S
          |-----------------|
               |     /|\
              \|/     |
          |-----------------|
          |   Rule Engine   |
          |-----------------|
               |      |
        Backends Services Bridges

Design

Event | Message -> Rules -> Actions -> Resources

   P -> |--------------------|    |---------------------------------------|
        | Messages (Routing) | -> | Rules (Select Data, Match Conditions) |
   S <- |--------------------|    |---------------------------------------|
          |---------|    |-----------|    |-------------------------------|
        ->| Actions | -> | Resources | -> | (Backends, Bridges, WebHooks) |
          |---------|    |-----------|    |-------------------------------|

Rule

A rule consists of a SELECT statement, a topic filter, and a rule action

Rules consist of the following:

• Id
• Name
• Topic
• Description
• Action
• Enabled

The operations on a rule:

• Create
• Enable
• Disable
• Delete

Action

Actions consist of the following:

• Id
• Name
• For
• App
• Module
• Func
• Args
• Descr

Define a rule action in ADT:

action :: Application -> Resource -> Params -> IO ()

A rule action:

Module:function(Args)

Resource

Resource Name

backend:mysql:localhost:port:db
backend:redis:localhost:
webhook:url
bridge:kafka:
bridge:rabbit:localhost

Resource Properties

• Name
• Descr or Description
• Config #{}
• Instances
• State: Running | Stopped

Resource Management

1. Create Resource
2. List Resources
3. Lookup Resource
4. Delete Resource
5. Test Resource

Resource State (Lifecircle)

1. Create Resource and Validate a Resource
2. Start/Connect Resource
3. Bind resource name to instance
4. Stop/Disconnect Resource
5. Unbind resource name with instance
6. Is Resource Alive?

Resource Type

The properties and behaviors of resources is defined by resource types. A resoure type is provided(contributed) by a plugin.

Resource Type Provider

Provider of resource type is a EMQX Plugin.

Resource Manager

              Supervisor
                   |
                  \|/
Action ----> Proxy(Batch|Write) ----> Connection -----> ExternalResource
  |                                      /|\
  |------------------Fetch----------------|

REST API

Rules API Actions API Resources API

CLI

rules list
rules show <RuleId>

rule-actions list
rule-actions show <ActionId>

resources list
resources show <ResourceId>

resource_templates list
resource_templates show <ResourceType>