Chirpstack-mqtt-forwarder publishes at QoS 0 — any way to enable QoS 1 for offline buffering?

Question

Hi,

I'm running a Dragino gateway (Armbian, armv7l) with chirpstack-mqtt-forwarder 4.4.0 and a local Mosquitto 2.0.21 bridging to a remote ChirpStack v4 server over WireGuard.

Architecture:

SX1302 concentrator
↓ Semtech UDP :1700
chirpstack-mqtt-forwarder 4.4.0
↓ MQTT (localhost:1883)
Mosquitto 2.0.21 (local, bridge mode)
↓ bridge over WireGuard
Mosquitto 2.0.22 (VPS) → ChirpStack v4.18

Problem: during internet outages, roughly 33-62% of uplinks are lost and never delivered after reconnection, despite a bridge configuration built for buffering.

Bridge config:

queue_qos0_messages true
max_queued_messages 100000
cleansession false
local_cleansession false
topic eu868/# out 1
topic eu868/# in 1
max_inflight_messages 1
restart_timeout 5 30

What I verified with logs during outages:

Frames are correctly received by the local broker: Received PUBLISH from (d0, q0, r0, m0, 'eu868/gateway/.../event/up', ...)
Note the q0 — the forwarder publishes at QoS 0
After reconnection, only a fraction of the queued frames appear as "Sending PUBLISH to local...-bridge"

What I already tested without success:

Upgraded Mosquitto 2.0.11 → 2.0.21 (no measurable change over a 10h outage test)
Explicit client_id in the forwarder config
Direct connection (forwarder → remote broker, bypassing local Mosquitto) — worse, no buffering at all, only "MQTT error: Network unreachable" repeated every second with no queued replay
AT+CFM=0 on the end device (this one did help: 59% → 33% loss)

My question: since queue_qos0_messages is documented as non-standard and QoS 0 has no delivery guarantee, is there any way to make chirpstack-mqtt-forwarder publish at QoS 1? I could not find a qos option in the configuration reference.

If not, is there a recommended approach for reliable store-and-forward on the gateway during long outages? My use case is water metering where gaps create visible artifacts in consumption graphs.

Thanks a lot for any pointers.

Orne Brocaar · Answer

Please see the ChirpStack MQTT Forwarder configuration documentation:
https://www.chirpstack.io/docs/chirpstack-mqtt-forwarder/configuration.html

There is a qos option under the [mqtt] section:

  # Quality of service level
  #
  # 0: at most once
  # 1: at least once
  # 2: exactly once
  #
  # Note: an increase of this value will decrease the performance.
  # For more information: https://www.hivemq.com/blog/mqtt-essentials-part-6-mqtt-quality-of-service-levels
  qos=0

Chirpstack-mqtt-forwarder publishes at QoS 0 — any way to enable QoS 1 for offline buffering?

1 Answers