Fix NanoMQ Bridge QoS Errors: A Practical Guide

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Hey guys! Ever run into those pesky QoS msg ack failed errors when using NanoMQ bridge? It can be a real head-scratcher, but don't worry, we'll break it down and figure out how to fix it. This article will dive deep into diagnosing and resolving these issues, especially when you're dealing with message caching. Let's get started!

Understanding the NanoMQ Bridge and Message Caching

Before we jump into the error itself, let's quickly recap what the NanoMQ bridge does and how message caching comes into play.

The NanoMQ bridge acts like a messenger, forwarding MQTT messages between different brokers or instances. This is super useful when you have distributed systems or need to connect different parts of your IoT infrastructure. Think of it as a reliable postman ensuring your messages get where they need to go, even across different networks or systems. Now, things can get tricky when the target broker is temporarily unavailable. That's where message caching steps in to save the day.

Message caching is a neat feature that allows NanoMQ to store messages temporarily when the target broker is offline. This ensures that no messages are lost during network hiccups or downtime. Once the target is back online, the cached messages are delivered, maintaining the reliability of your system. Imagine it as a temporary holding area for your messages, making sure they're delivered as soon as the recipient is ready. When you configure a bridge with message caching, you're essentially telling NanoMQ to be extra cautious and ensure message delivery even in challenging conditions. This is especially important for applications where data loss is not an option, such as industrial IoT or critical infrastructure monitoring. By using message caching, you can build robust and fault-tolerant systems that can handle unexpected interruptions without losing crucial data. Understanding how this system works is the first step in tackling those pesky error messages, so let’s dive deeper into how to configure it properly and what can go wrong.

Decoding the "QoS msg ack failed" Error

So, you're seeing this error: nanomq_satellite | 2025-08-05 13:37:35 [38] WARN /nanomq/nng/src/mqtt/protocol/mqtt/mqtt_client.c:1113 mqtt_recv_cb: QoS msg ack failed xxx. What does it actually mean?

This warning message indicates that NanoMQ, acting as an MQTT client in the bridge, failed to receive an acknowledgment (ACK) for a QoS (Quality of Service) message it sent. In MQTT, QoS levels define the guarantee of message delivery. A QoS level of 1, which is what you're using (qos=1), means that the message should be delivered at least once. To achieve this, the sender expects an acknowledgment from the receiver. When this acknowledgment doesn't arrive within a certain timeframe, the QoS msg ack failed error pops up. This is essentially NanoMQ's way of saying, “Hey, I sent a message, but I didn’t hear back from the other side!”

There could be several reasons why this happens. A common cause is network congestion or temporary disconnections, which can prevent the ACK from reaching the sender in time. Another reason could be issues on the receiving end, such as the target broker being overloaded or experiencing internal errors. It's also possible that there's a configuration mismatch or a bug in the system that's preventing the acknowledgments from being processed correctly. To effectively troubleshoot this error, you need to investigate the network connection between the brokers, the status of the target broker, and the NanoMQ bridge configuration. Understanding the root cause will help you implement the right solution, whether it's adjusting timeout settings, improving network reliability, or addressing issues on the receiving end. Let's dig into the potential causes and how to address them.

Analyzing Your NanoMQ Bridge Configuration

Let's take a closer look at your NanoMQ bridge configuration. You've shared a snippet, and it's a great starting point for troubleshooting. Here's the configuration you provided:

bridges.mqtt.nameOfBridge= {
 enable = true
 proto_ver = 5
 name = "nameOfBridge"
 server = "mqtt-tcp://main:1883"
 forwards = [
 {
 remote_topic = ""
 local_topic = "#"
 prefix = "group1/system1/"
 }
 ]
 keepalive = "30s"
 max_send_queue_len = 10000
 max_recv_queue_len = 10000
 resend_interval = 50
 resend_wait = 3000
 cancel_timeout = 10000
}

bridges.mqtt.cache = {
 disk_cache_size = 102400
 mounted_file_path="/tmp/"
 flush_mem_threshold = 3
}

sqlite = {
 disk_cache_size = 102400
 mounted_file_path = "/tmp/"
 flush_mem_threshold = 3
 resend_interval = 5000
}

From this configuration, we can see that you've set up a bridge named nameOfBridge that connects to an MQTT broker at mqtt-tcp://main:1883. You're forwarding all topics (#) with a prefix of group1/system1/. You've also configured message caching with a disk cache size of 102400 and a flush memory threshold of 3. The sqlite section seems related to persistent storage for messages. Let's break down some key parameters that might be contributing to the QoS msg ack failed error.

  • resend_interval: This parameter, set to 50, likely represents the interval (in milliseconds) at which NanoMQ will attempt to resend unacknowledged messages. A lower value means more frequent resends. It's essential to strike a balance here. If the interval is too short, it might overwhelm the network and the target broker. If it's too long, messages might take a while to be delivered after a disconnection. This value plays a critical role in how quickly NanoMQ tries to recover from a failed acknowledgment.
  • resend_wait: Set to 3000 (milliseconds), this is the time NanoMQ waits for an acknowledgment before considering a message as failed. If an ACK isn't received within this timeframe, NanoMQ will trigger a resend. A shorter resend_wait might lead to premature resends if network latency is high. A longer resend_wait might delay message delivery in case of genuine failures. Think of this as the grace period NanoMQ gives before deciding a message needs to be resent.
  • cancel_timeout: This parameter, set to 10000 (milliseconds), likely determines how long NanoMQ will keep trying to deliver a message before giving up entirely. Once this timeout is reached, the message might be discarded or handled based on other configurations. This acts as a final safety net to prevent messages from being stuck indefinitely in the system. It's important to set this value appropriately to ensure messages are delivered within a reasonable timeframe without being discarded prematurely.

These parameters are crucial for managing message delivery reliability and can directly impact the QoS msg ack failed errors you're seeing. We'll explore how to adjust them to optimize your setup.

Potential Causes and Solutions

Okay, let's dive into the possible reasons behind the QoS msg ack failed errors and how we can tackle them. Here are a few common culprits and their solutions:

1. Network Connectivity Issues

Problem: The most frequent reason for acknowledgment failures is, you guessed it, network problems. If there are temporary disconnections, high latency, or packet loss between your NanoMQ instances, acknowledgments might not make it back in time.

Solution:

  • Check Network Stability: First things first, verify your network connection. Are there any known outages or intermittent issues? Use tools like ping or traceroute to diagnose connectivity between the NanoMQ instances.

  • Increase resend_wait: Try increasing the resend_wait parameter in your configuration. This gives the network a bit more time to deliver acknowledgments. For example, you could try setting it to 5000 or even 10000 milliseconds.

    resend_wait = 5000 # Try increasing this value

  • Evaluate Network Infrastructure: If the problem persists, investigate your network infrastructure. Are there any bottlenecks or overloaded devices? Consider upgrading network hardware or optimizing network configurations.

2. Target Broker Overload

Problem: If the target broker (the one receiving messages from the bridge) is overwhelmed, it might not be able to process messages and send acknowledgments quickly enough.

Solution:

  • Monitor Broker Performance: Use monitoring tools to check the target broker's CPU usage, memory consumption, and message processing rates. High resource utilization can indicate overload.
  • Increase Broker Capacity: If the broker is consistently overloaded, consider scaling up its resources (e.g., adding more CPU or memory) or distributing the load across multiple brokers.
  • Adjust QoS Levels: If possible, consider reducing the QoS level for some topics. QoS 1 guarantees at-least-once delivery, but QoS 0 (at-most-once) might be sufficient for some non-critical data. This can reduce the processing load on the broker.
  • Implement Rate Limiting: Implement rate limiting on the bridge or the publishing clients to prevent the target broker from being overwhelmed. NanoMQ and other MQTT brokers often provide mechanisms for rate limiting.

3. Configuration Mismatches

Problem: Sometimes, the issue isn't a fault but a misconfiguration. Incorrect settings in your bridge or broker configurations can lead to acknowledgment failures.

Solution:

  • Double-Check Configurations: Carefully review your NanoMQ bridge configuration, as well as the configurations of both brokers involved. Pay attention to parameters like keepalive, max_send_queue_len, max_recv_queue_len, and any authentication or authorization settings.
  • Ensure Compatibility: Make sure that the MQTT protocol versions and QoS levels are compatible between the bridge and the brokers. Mismatched settings can cause communication issues.
  • Review Error Logs: Check the error logs of both NanoMQ instances and the brokers for any specific error messages or warnings that might indicate a configuration issue.

4. Message Caching Issues

Problem: While message caching is great for reliability, it can sometimes contribute to acknowledgment issues if not configured correctly. For instance, if the disk cache is full or there are problems with the storage backend, messages might not be persisted or delivered properly.

Solution:

  • Monitor Disk Usage: Ensure that the disk where the message cache is stored has sufficient free space. A full disk can prevent messages from being cached, leading to delivery failures.

  • Check Cache Configuration: Verify the disk_cache_size and mounted_file_path settings in your configuration. Make sure the path is valid and accessible, and the cache size is appropriate for your message volume.

bridges.mqtt.cache = { disk_cache_size = 102400 # Check if this is sufficient mounted_file_path="/tmp/" # Ensure this path is valid flush_mem_threshold = 3 } ```

  • Review Persistence Settings: If you're using persistent storage (like SQLite, as indicated in your configuration), check the settings related to disk cache size, mounted file path, and flush memory threshold. Ensure these settings are optimized for your system.

sqlite = { disk_cache_size = 102400 mounted_file_path = "/tmp/" flush_mem_threshold = 3 resend_interval = 5000 } ```

  • Test Cache Functionality: Manually test the message caching functionality by temporarily disconnecting the target broker and sending messages. Verify that the messages are cached and delivered when the broker comes back online.

5. NanoMQ Bugs or Limitations

Problem: It's rare, but sometimes the issue might stem from a bug or limitation in NanoMQ itself.

Solution:

  • Check for Updates: Make sure you're running the latest version of NanoMQ. Bug fixes and performance improvements are often included in new releases.
  • Consult Documentation and Community: Review the NanoMQ documentation and community forums for known issues or workarounds. Other users might have encountered similar problems and found solutions.
  • Report the Issue: If you suspect a bug, report it to the NanoMQ developers. Providing detailed information about your setup, configuration, and the steps to reproduce the issue can help them diagnose and fix the problem.

Applying the Solutions to Your Scenario

Now, let's relate these solutions back to your specific scenario. You mentioned sending 5000 messages with QoS 1 and seeing the QoS msg ack failed errors when the target broker becomes available again. This suggests that message caching is working (messages are being stored), but there's an issue with acknowledgments after the broker comes back online.

Given your configuration and the error message, here's a targeted approach:

  1. Increase resend_wait: Start by increasing the resend_wait parameter. The default of 3000 milliseconds might be too short, especially after a broker outage. Try setting it to 5000 or 10000 milliseconds.

    resend_wait = 5000 # or 10000

  2. Monitor Broker Load: Check the CPU and memory usage of the target broker when it comes back online. It might be struggling to process the backlog of cached messages, leading to acknowledgment delays.

  3. Review Disk Cache: Ensure that the disk where you're storing the cached messages (/tmp/ in your case) has enough free space. Although /tmp/ is often used for temporary files, it's crucial to make sure it's not filling up.

  4. Consider resend_interval: While a smaller resend_interval might seem like a good idea for faster retries, it could also contribute to network congestion. If you've increased resend_wait and still see issues, you might want to slightly increase resend_interval as well.

  5. Check Logs: Dive deep into the NanoMQ and broker logs. Look for any other error messages or warnings that might provide clues about what's going wrong. Logs are your best friend when troubleshooting!

By systematically addressing these points, you'll be well on your way to resolving those QoS msg ack failed errors and ensuring reliable message delivery with your NanoMQ bridge.

Conclusion

Troubleshooting QoS msg ack failed errors in NanoMQ bridges can feel like a puzzle, but by understanding the underlying mechanisms and systematically investigating potential causes, you can definitely crack it! We've covered a range of solutions, from checking network connectivity and broker load to tweaking configuration parameters and reviewing message caching settings. Remember, a bit of detective work and careful adjustments can go a long way. Keep an eye on your logs, monitor your system's performance, and don't hesitate to experiment with different settings to find what works best for your setup. You got this, and happy bridging!