fix

haproxy/config/haproxy copy.cfg

+global
+    daemon
+    maxconn 256
+
+defaults
+    mode tcp
+    timeout connect 5000ms
+    timeout client 50000ms
+    timeout server 50000ms
+
+frontend mqtt_frontend
+    bind *:1883
+    mode tcp
+    default_backend mqtt_backend
+
+backend mqtt_backend
+    mode tcp
+    balance roundrobin
+    option tcp-check
+    tcp-check send-binary 303c01000004000000000000
+    tcp-check expect binary 200201000004000000000000
+    tcp-check send-binary 100000016d7174742f04020000000c6d7174742d737461747573
+    tcp-check expect binary 20020001000c6d7174742d737461747573
+    server mqtt_server1 192.168.1.101:1883 check inter 5s rise 2 fall 3
+    server mqtt_server2 192.168.1.102:1883 check inter 5s rise 2 fall 3
+    server mqtt_server3 192.168.1.103:1883 check inter 5s rise 2 fall 3
+
+lua-load /etc/haproxy/mqtt_health_check.lua

haproxy/config/mqtt_health_check.lua

+core.register_action("mqtt_health_check", {"tcp-req"}, function(txn)
+    txn:set_var(txn.TXN_CHECK_STATUS, "L7OK")
+    txn:set_var(txn.TXN_CHECK_CODE, "200")
+    txn:set_var(txn.TXN_CHECK_PAYLOAD, "")
+    if txn.f:has_subscribers() then
+    local ok, err = txn.f:publish("mqtt_health_check", "PINGREQ")
+    if not ok then
+    txn:set_var(txn.TXN_CHECK_STATUS, "L7FAIL")
+    txn:set_var(txn.TXN_CHECK_CODE, "503")
+    end
+    end
+    end)
+    
+    
+core.register_subscriber("mqtt_health_check", function(applet)
+    applet:set_status(200)
+    applet:add_header("Content-Type", "text/plain")
+    applet:start_response()
+    applet:send("PONG\n")
+    end)