So, does that mean there are 2 MQTT brokers running on the machine? One in the MQTT container and one in the Zigbee2MQTT container? If that’s the case, I think it’s redundant in terms of resources, and I don’t understand the purpose. Is there a technical reason, or is the Zigbee2MQTT container designed that way?
There are 2 brokers in 2 containers.
This allows for simple isolation, as a broker is very resource-efficient.
This allows, among other things, to be able to disable the MQTT integration in Gladys settings if the user no longer needs it. The zigbee2mqtt integration, independently, will still be able to function.
In the future, if another integration with another protocol requires an MQTT broker, it will also have its own MQTT container. As @VonOx said, this allows to completely isolate the integration and to be sure that the broker is configured as it should be for it. Several integrations could very well use the same topics to communicate with Gladys for example, thus preventing any conflicts.
Hopefully the explanations have been clear.
@VonOx @Terdious
Ok, given your two responses and seen from this angle, it makes sense both in the technical choice (relevant in this case) and in the response given to @Retlaw (more judicious with these elements)! 
This discussion will at least have provided more precise insights into the technical side of integrations in gladys 
It’s true that isolation in containers makes everything more robust in terms of operation and more portable! 
The next container, is it vosk? Or kalliope? 
I’m getting back to you guys with a question that’s been bothering me. On the Gladys side, there’s a strong password for MQTT integration, but for Zigbee2MQTT integration, there isn’t one (at least that’s what I saw when I went to port 8080). How is security managed at this level in this case?
There are none 
An issue has been created about this [Zigbee2Mqtt] As a User, I want the zigbee2mqtt interface to be more secured · Issue #1407 · GladysAssistant/Gladys · GitHub
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