# mqtt

Hot Reloadable

Only `ack_wait`, `max_ack_pending`, the consumer settings and the TLS certificate material reload. Changing the MQTT `host`, `port`, `authorization`, `no_auth_user` or `js_domain` fails the reload.

Configuration for enabling the MQTT interface.

## Properties

| Name                                                                                   | Description                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | Type       | Default   | Reloadable |
| -------------------------------------------------------------------------------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ---------- | --------- | ---------- |
| [`host`](/reference/config/mqtt/host.md)                                               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        | `string`   | `0.0.0.0` | No         |
| [`port`](/reference/config/mqtt/port.md)                                               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        | `integer`  | `1883`    | No\*       |
| [`listen`](/reference/config/mqtt/listen.md)                                           |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        | `string`   | -         | No         |
| [`tls`](/reference/config/mqtt/tls/.md)                                                |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        | `object`   | -         | Yes\*      |
| [`authorization`](/reference/config/mqtt/authorization/.md)                            |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        | `object`   | -         | No         |
| [`no_auth_user`](/reference/config/mqtt/no_auth_user.md)                               | If no user name is provided when an MQTT client connects, will default this user name in the authentication phase. If specified, this will override, for MQTT clients, any `no_auth_user` value defined in the main configuration file. *Note: that this is not compatible with running the server in operator mode.*                                                                                                                                                                                                                                                                                                                  | `string`   | -         | No         |
| [`ack_wait`](/reference/config/mqtt/ack_wait.md)                                       | This is the amount of time after which a QoS 1 message sent to a client is redelivered as a `DUPLICATE` if the server has not received the `PUBACK` packet on the original Packet Identifier. will cause the server to use the default value (30 seconds). Note that changes to this option is applied only to new MQTT subscriptions.                                                                                                                                                                                                                                                                                                 | `duration` | `30s`     | Yes\*      |
| [`max_ack_pending`](/reference/config/mqtt/max_ack_pending.md)                         | This is the amount of QoS 1 messages the server can send to a subscription without receiving any `PUBACK` for those messages. The valid range is \[0..65535]. The total of subscriptions' max\_ack\_pending on a given session cannot exceed 65535. Attempting to create a subscription that would bring the total above the limit would result in the server returning `0x80` in the `SUBACK` for this subscription. Due to how the NATS Server handles the MQTT `#` wildcard, each subscription ending with `#` will use 2 times the `max_ack_pending` value. Note that changes to this option is applied only to new subscriptions. | `integer`  | `100`     | Yes\*      |
| [`js_domain`](/reference/config/mqtt/js_domain.md)                                     | If specified, sets an explicit JetStream domain to be used by MQTT.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | `string`   | -         | No         |
| [`consumer_memory_storage`](/reference/config/mqtt/consumer_memory_storage.md)         | Hold MQTT consumer state in memory rather than on disk.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                | `boolean`  | `false`   | Yes\*      |
| [`consumer_replicas`](/reference/config/mqtt/consumer_replicas.md)                     | Deprecated. The server logs a warning and ignores the value; consumer replication follows the stream.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  | `integer`  | -         | Ignored\*  |
| [`js_api_timeout`](/reference/config/mqtt/js_api_timeout.md)                           | How long MQTT waits for a JetStream API call before giving up.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         | `duration` | `5s`      | No         |
| [`reject_qos2_publish`](/reference/config/mqtt/reject_qos2_publish.md)                 | Reject QoS 2 publishes instead of accepting them, for clients that must not silently get weaker delivery guarantees.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | `boolean`  | `false`   | No         |
| [`downgrade_qos2_subscribe`](/reference/config/mqtt/downgrade_qos2_subscribe.md)       | Accept a QoS 2 subscription but serve it at QoS 1.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     | `boolean`  | `false`   | No         |
| [`stream_replicas`](/reference/config/mqtt/stream_replicas.md)                         | If specified, sets an explicit number of stream replicas to be used for MQTT-backed streams.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           | `integer`  | -         | Yes\*      |
| [`consumer_inactive_threshold`](/reference/config/mqtt/consumer_inactive_threshold.md) | Set an explicit default inactive threshold for consumers used by MQTT.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 | `duration` | -         | Yes\*      |

\* See the property page for reload caveats.