Incus OVN Network Edit Issue With Load Balancer - Troubleshooting

Introduction

Hey guys! Ever run into a situation where you just can't seem to edit your Incus OVN network settings, especially when you've got a load balancer in the mix? It's a real head-scratcher, but don't worry, you're not alone. This article dives deep into a specific issue where users find themselves unable to modify their OVN network configurations in Incus once a load balancer with backends is defined. We'll explore the ins and outs of the problem, replicate the steps to reproduce it, and hopefully shed some light on why this is happening. So, let's get started and figure this out together!

The Problem: OVN Networks and Load Balancer Backends

So, what's the deal? The core issue here is that when you have an OVN network in Incus and you create a load balancer with defined backends, you might hit a wall when trying to edit the network settings. It's like the system throws a fit and incorrectly claims that your backend target address isn't within the network's subnet. This can be super frustrating, especially when you're trying to tweak things or make important changes to your network. We're going to break down the steps to reproduce this issue so you can see exactly what's going on and how to identify it in your own setup. Let’s dive in and get our hands dirty with the technical details, alright?

Incus System Details: Setting the Stage

Before we get into the nitty-gritty, let's lay the groundwork by examining the Incus system details where this issue was observed. Understanding the environment is key to troubleshooting effectively. The Incus setup in question includes a cluster configuration with three nodes, each running Incus version 6.15. The nodes are configured with a Ceph storage backend, and OVN is used for networking. Key configurations include:

• ACME settings for Let's Encrypt certificate management.
• A cluster HTTPS address defined for communication between nodes.
• OVN Northbound connection details specifying the addresses for OVN communication.
• A wide range of API extensions enabled, indicating a feature-rich Incus installation.

The incus info command provides a wealth of information about the system's configuration and capabilities. This information is crucial for identifying potential compatibility issues or misconfigurations that may contribute to the problem. For instance, the enabled API extensions reveal the features supported by the Incus installation, while the environment details provide insights into the underlying infrastructure. Knowing these details helps us to narrow down the possible causes of the issue and develop targeted solutions. So, keep these details in mind as we move forward, because they are essential for understanding the context of the problem and finding the right fix.

Reproducing the Issue: Step-by-Step

Okay, let's get down to business and walk through the steps to reproduce this pesky issue. By replicating the problem, we can better understand what's going on under the hood and pinpoint the exact moment things go sideways. Follow along, and you'll see how this OVN network editing problem crops up with load balancers.

1. Initial OVN Network Setup: First things first, we need an OVN network to play with. The network is set up with a specific IPv4 address range (192.168.18.1/23), a defined DNS domain, and an OVN uplink. This is your basic OVN network configuration, ready for some action.

root@incus1:~# incus network show default
config:
 bridge.mtu: "1500"
 dns.domain: <omitted>
 dns.zone.forward: <omitted>
 ipv4.address: 192.168.18.1/23
 ipv6.address: none
 ipv6.dhcp: "false"
 network: ovn_uplink
 volatile.network.ipv4.address: 192.168.15.100
description: ""
name: default
type: ovn
used_by:
<truncated output>
managed: true
status: Created
locations:
- incus1
- incus2
- incus3
project: default

2. Successful Network Editing (No Load Balancer): Now, let's make sure we can edit the network under normal circumstances. We'll set a custom user.test property to true and then verify that the change sticks. This step confirms that the network is editable when there are no load balancers in the picture. It’s like a baseline test to ensure everything’s working as it should.

root@incus1:~# incus network set default user.test=true
root@incus1:~# incus network get default user.test
true

3. Adding a Load Balancer (No Backends): Next up, we introduce a load balancer to the mix. We create one with the IP address 192.168.14.100, but without adding any backend servers just yet. At this stage, we can still edit the network settings without any hiccups. This tells us that the mere existence of a load balancer isn't the trigger for the issue; it's something else.

root@incus1:~# incus network load-balancer create default 192.168.14.100
Network load balancer 192.168.14.100 created
root@incus1:~# incus network set default user.test=false
root@incus1:~# incus network get default user.test
false

4. The Breaking Point: Adding a Backend: Here's where the magic (or rather, the bug) happens. We add a backend to the load balancer, targeting the address 192.168.18.10. As soon as we do this, attempting to edit the network throws an error. The error message incorrectly claims that the target address (192.168.18.10) isn't within the network's subnet, even though it clearly is. This is the crux of the problem—the backend triggers a validation error that shouldn't be occurring.

root@incus1:~# incus network load-balancer backend add default 192.168.14.100 test 192.168.18.10
root@incus1:~# incus network set default user.test=true
Error: failed to notify peer 192.168.10.8:8443: Network load balancer for "192.168.14.100" has a backend target address "192.168.18.10" that is not within the network subnet

5. Resolution by Removing the Backend: To confirm our suspicions, we remove the backend from the load balancer. Once the backend is gone, we can edit the network again without any issues. This step reinforces the idea that the presence of a backend on the load balancer is directly linked to the editing problem. It's like the backend is the key that unlocks the bug.

root@incus1:~# incus network load-balancer backend remove default 192.168.14.100 test
root@incus1:~# incus network get default user.test
false
root@incus1:~# incus network set default user.test=true
root@incus1:~# incus network get default user.test
true

By following these steps, you can reliably reproduce the issue and see for yourself how the interaction between OVN networks and load balancer backends can lead to editing problems. Now that we've replicated the bug, let's dig deeper into why this might be happening and what we can do about it.

Current Behavior: The Error in Action

So, what exactly happens when we try to edit the OVN network with a load balancer backend in place? The current behavior is pretty clear: Incus throws an error. But it's not just any error; it's a specific one that gives us a crucial clue. The error message states that the network load balancer has a backend target address that isn't within the network subnet. Now, here's the kicker: the address is actually within the subnet. This is a false positive, meaning the system is incorrectly flagging the address as out of bounds.

This misidentification is a key piece of the puzzle. It suggests that there's a flaw in the validation logic somewhere within Incus. The system is running a check to ensure backend addresses are within the network's IP range, which is a good practice in general. However, in this specific scenario, the check is failing erroneously. This could be due to a number of reasons, such as an incorrect subnet calculation, a misreading of the network configuration, or a bug in the comparison logic. Understanding this current behavior is essential for formulating a hypothesis about the root cause and devising a fix. So, let's keep this in mind as we move on to figuring out what's really going on behind the scenes, okay?

Expected Behavior: What Should Happen

Alright, let's talk about what should be happening. In an ideal world, you should be able to edit your OVN network configurations regardless of whether you have load balancers with backends defined. Adding a load balancer or specifying backend servers shouldn't put a lock on your network settings. You should have the flexibility to tweak things as needed, without running into misleading error messages. This is crucial for maintaining a dynamic and adaptable infrastructure. Imagine if every time you added a backend to your load balancer, you had to jump through hoops just to change a simple network setting. That's a recipe for frustration and inefficiency!

The expected behavior here is straightforward: Incus should allow you to modify network properties, such as custom user settings or other network-wide configurations, without being blocked by the presence of load balancer backends. The validation checks should accurately reflect the network's IP range, and any changes should be applied seamlessly. This ensures that you can manage your network resources effectively and keep your infrastructure running smoothly. So, with this clear expectation in mind, let's dive deeper into why the actual behavior is falling short and what we can do to bridge that gap, yeah?

Diving Deeper: Potential Causes and Solutions

Okay, guys, let's put on our detective hats and start digging into the potential causes behind this OVN network editing issue. We've seen the problem, we've reproduced it, and we know what should be happening. Now, it's time to figure out why it's not working as expected.

1. Subnet Validation Bug

The most likely culprit here is a bug in the subnet validation logic within Incus. As we've seen, the error message incorrectly claims that a backend IP address is outside the network's subnet. This suggests that the function responsible for checking IP address ranges is either miscalculating the subnet or misinterpreting the IP address. It could be a simple off-by-one error, a misunderstanding of CIDR notation, or a more complex issue in how Incus handles OVN network configurations. To tackle this, the Incus codebase needs a thorough examination, specifically the parts dealing with network address validation. Debugging tools and logging can help pinpoint the exact location of the error. Once identified, a fix can be implemented to ensure accurate subnet validation.

2. Inter-Node Communication Issues

Another possibility is that the error arises from communication issues between the nodes in the Incus cluster. The error message