# Store Device Offline Messages Using Data Integrations

We will simulate temperature and humidity data and report them to the EMQX Cloud via the MQTT protocol, and then use EMQX Cloud data integration to save offline messages to cloud service resources (third-party database or message queue), which is implemented in this article using Redis as an example.

WARING

QoS > 0 required to save offline messages

Before you start, you need to complete the following operations:

  • Deployments have already been created on EMQX Cloud (EMQX Cluster).
  • For Professional Plan users: Please complete Peering Connection Creation first, all IPs mentioned below refer to the intranet IP of the resource.(Professional Plan with a NAT gateway can also use public IP to connect to resources)
  • For Standard Plan users: No peering connection is required, all IPs below refer to the public IP of the resource.

# Redis configuration

  1. Install Redis

    docker run -itd --name redis -p 6379:6379 redis
    
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# Data Integrations configuration

Go to Deployment Details and click on EMQX Dashbaord to go to Dashbaord.

  1. New Resource

    Click on Rules on the left menu bar → Resources, click on New Resource and drop down to select the Redis single-node mode resource type. Fill in the Redis information you have just created and click Test. If there is an error, instantly check that the database configuration is correct. create resource

  2. Rule Testing Click on Rules on the left menu bar → Rules, click on Create and enter the following rule to match the SQL statement. We will read out its message information, if the topic is temp_hum/emqx.

    The FROM statement of the rule SQL explains.

    temp_hum/emqx: Publisher posts a message to "temp_hum/emqx" triggers saving offline messages to Redis

    $events/session_subscribed: Subscriber subscribes to topic "temp_hum/emqx" triggers fetching offline messages

    $events/message_acked: Subscriber replies to the message ACK and triggers the deletion of the received offline message

    SELECT
        *
    FROM
        "temp_hum/emqx",
        "$events/session_subscribed",
        "$events/message_acked"
    WHERE
        topic =~ 'temp_hum/emqx'
    
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    test sql

  3. Add a response action

    Click on Add Action in the bottom left corner, drop down and select → Offline Message → Save Offline Message to Redis, select the resource created in the first step.

    Tip

    Here you need to plan for the Redis Key expiration time, and it is recommended to save no more than 100 messages offline

    create action

  4. Click on New Rule and return to the list of rules rule list

  5. View rules monitoring monitor

# Test

  1. Use MQTT X (opens new window) to simulate temperature and humidity data reporting

    You need to replace broker.emqx.io with the created deployment connection address, and add client authentication information to the EMQX Dashboard.

    Tip

    QoS > 0 required to send messages

    MQTTX

  2. View data dump results

    $ docker exec -it redis bash
    $ redis-cli
    $ keys *
    
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    redis

  3. Use MQTT X (opens new window) to consume offline data In MQTT X, subscribe to topic temp_hum/emqx to get offline data.

    Tip

    The QoS of the subscription topic must be greater than 0, otherwise the message will be received repeatedly.

    mqttx mqttx

  4. View the data consumed by redis

    $ docker exec -it redis bash
    $ redis-cli
    $ keys *
    
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    redis