This module provides two metrics:

Bytes of memory as reported by collectgarbage("count")
Provides the current Lua version as a label
# HELP lua_info Lua runtime version
# UNIT lua_info
# TYPE lua_info gauge
lua_info{version="Lua 5.4"} 1
# HELP lua_heap_bytes Memory used by objects under control of the Lua
garbage collector
# UNIT lua_heap_bytes bytes
# TYPE lua_heap_bytes gauge
lua_heap_bytes 8613218


With the plugin installer in Prosody 0.12 you can use:

sudo prosodyctl install --server= mod_measure_lua

For earlier versions see the documentation for installing 3rd party modules