I couldn’t find anywhere in documentation the answers.
Are there any limits on number of entities/devices/areas/etc. imposed by the OS?
Use Case: Retention policy for custom notification entities.
Are there any API rate limits or MQTT messaging limits?
Use Case: synchronizing state to external services via MQTT.
I am no expert on this so this could be wrong:
Probably but you will never exceed them. There are people here who automate factories and have no issues.
Not that I’m aware of. API calls are quite cpu intensive though. You’ll be cpu bound and tasks may get destroyed. Or MQTT message floods may lose messages if you overwhelm the network stack. Using mqtt QoS > 0 may help or may make it worse, as the messages are no longer “spray and pray” but have acknowledgements. However this will increase the amount of traffic possibly exacerbating the issue. Having said that mqtt is a really lightweight messaging protocol and you would be really hard pressed to actually cause this on a 100Mb/s link.
In short, for all practical purposes your answers are no, and no.
Thank you for your reply, Tom.
I’ve tested a bit generating custom entities in bulk (running HA on WSL2-backend in Docker on my ThinkPad for dev), and once you hit 7000 entities, even the native UI is sluggish and almost unusable, and the whole box crashes if I query the states from a custom Lit Element.
for my purposes, I chose 3000 entities as a reasonable threshold to base my retention settings on.