How to migrate an application using AWS IoT Jobs from v3 to 202009.00 and subsequent releases.

The AWS IoT Jobs client library has been refactored for this release. The refactored library has the following differences as compared to the jobs client library in v3 of the AWS IoT Device SDK for Embedded C:

• The refactored library provides simple convenience macros and functions for handling MQTT topic strings as defined by the AWS IoT Jobs Service.
• The refactored library is completely decoupled from the underlying MQTT implementation, permitting any MQTT client library to be used.
• The refactored library does not construct JSON message bodies, permitting any JSON library to be used.

The v3 jobs client library, on the other hand, is tightly coupled to the MQTT implementation present in v3 of the AWS IoT Device SDK for Embedded C. It consists of a heavyweight set of APIs with multiple dependencies. JSON parsing, for example, is built in to the API implementation.

Note: The AWS IoT Device SDK for Embedded C now offers the coreMQTT library and the coreJSON library as supported alternatives.

To migrate an existing application

• change the setup code to establish a connection with AWS IoT core
• add a subscription step to the setup code
  • use Jobs_GetTopic() to populate a buffer with the desired subscription topic
  • use the MQTT client library to subscribe to the topic
• in your MQTT receive callback, add a handler that calls Jobs_MatchTopic()
  • based on the response, react to a succeeded or failed API request
  • if a jobs document is present, parse it for details and launch the job
• replace each existing API request call with a set of steps
  • call the new API to populate a buffer with the desired topic
  • optionally add a JSON body for the MQTT message
  • use the MQTT client library to publish the request
• periodically send a status update when a job is running

A complete example using libmosquitto and coreJSON is available here.