Dual MQTT Brokers on ESP32

This code performs data publishing and subcribing on two MQTT Brokers simultaneously

GPIO Functions:

I am using ENC28J60 Ethernet Module and Devkit v1's integrated Wifi.

• GPIO 18 : SCLK
• GPIO 23 : MOSI
• GPIO 19 : MISO
• GPIO 5 : CS
• SPI CLOCK MHz : 8MHz
• NOTE : SDK Configurations for SPI has to be done on individual level

Understanding the Flow:

• This code is developed for ESP32 on Embedded C Language using FreeRTOS.
• MQTT is a lightweight, publish-subscribe network protocol that transports messages between devices. The protocol usually runs over TCP/IP.
• ESP32 will the client and the MQTT URL will be the Broker.
• A client can either subscribe to a specific topic on the MQTT broker and get the data/messages.
• Client can also publish to a specific topic on the MQTT broker
• In this example, I will connect to two separate MQTT Brokers from same ESP32 and create both subscribing and publishing logic.
• I am pinging "www.google.com" to verify Internet Services but you can also ping the MQTT broker itself ( which is much more optimal solution ).

Conclusion:

• Turns out, you can connect to multiple MQTT Brokers at the same time, but stability/reliablity is still not confirmed.
• VERY IMPORTANT: ESP gives WIFI connection priority over Ethernet by default ( at least in my test cases ). Hence, if your ESP is connected to an AP but isn't receiving any Internet Packages, it won't shift to Ethernet!!