VMUI Wrong URL Guess With Target_path_suffix: Bug & Fix

Are you experiencing issues with VictoriaMetrics User Interface (VMUI) guessing incorrect URLs when utilizing target_path_suffix? This problem can be particularly frustrating when trying to manage multi-tenant environments. This article will explore a specific bug report, dissect the issue, and provide a comprehensive understanding of the problem and its resolution.

Understanding the Bug: VMUI's URL Guessing Problem

In the realm of monitoring solutions, VictoriaMetrics stands out as a powerful and efficient time-series database. However, like any complex system, it's not immune to occasional bugs. One such issue arises when using VMUI with target_path_suffix in a multi-tenant setup. The core problem is that VMUI incorrectly constructs URLs, leading to failed requests and a broken user experience. Specifically, since version v1.125.0, VMUI attempts to access /api/v1/status instead of the correct /prometheus/api/v1/status endpoint. This discrepancy prevents users from effectively querying data and exploring cardinality, essentially rendering VMUI unusable in certain configurations.

To fully grasp the implications, let's break down the key components involved:

• VMUI: The user interface for interacting with VictoriaMetrics, providing a visual way to query data, explore metrics, and manage the system.
• target_path_suffix: A configuration option used in multi-tenant environments to restrict user access to specific tenants or data subsets. It appends a suffix to the URL path, effectively isolating tenants.
• VMAuth: VictoriaMetrics' authentication component, responsible for verifying user credentials and enforcing access control policies.
• VMUser: A custom resource definition (CRD) used to define users and their associated permissions within VictoriaMetrics.

When target_path_suffix is employed, the expected behavior is for VMUI to construct URLs that include this suffix, ensuring that requests are routed to the correct tenant. However, the bug causes VMUI to omit the necessary prefix (/prometheus), resulting in requests hitting the wrong endpoint and failing. This misdirection not only disrupts the user experience but also raises concerns about data security and access control.

Detailed Explanation with an Example

Imagine a scenario where you have a VictoriaMetrics cluster with multiple tenants, each identified by a unique suffix. You create a user with limited access, restricted to tenant "0" using target_path_suffix: /select/0. This means the user should only be able to query data within this specific tenant.

Prior to version v1.125.0, when this user logged into VMUI and attempted a query, the URL generated would correctly include the /prometheus prefix and the /select/0 suffix, such as /prometheus/api/v1/query?query=...&select/0. This ensures the request is routed to the correct tenant.

However, with version v1.125.0 and later, VMUI starts generating incorrect URLs like /api/v1/query?query=.... Notice the missing /prometheus prefix. This request will fail because it's hitting the wrong endpoint, effectively bypassing the intended tenant isolation.

This bug has significant implications for multi-tenant environments, as it can lead to:

• Data Access Issues: Users may be unable to query data within their assigned tenants.
• Security Vulnerabilities: If not properly addressed, this issue could potentially expose data from other tenants.
• Operational Disruptions: Incorrect URLs can lead to failed requests, broken dashboards, and overall instability.

Steps to Reproduce the Bug: A Practical Guide

To reproduce this bug, you'll need a VictoriaMetrics cluster with VMAuth and VMUser configured. Follow these steps:

1. Create a VMUser: Define a user with target_path_suffix to restrict access to a specific tenant. The following YAML snippet provides an example:

   apiVersion: operator.victoriametrics.com/v1beta1
   kind: VMUser
   metadata:
     name: testuser
     namespace: your-namespace
     labels:
       app.kubernetes.io/component: vmuser
   spec:
     username: testuser
     password: testpass
     targetRefs:
     - crd:
         kind: VMCluster/vmselect
         name: cluster
         namespace: your-namespace
       target_path_suffix: /select/0
       paths:
       - /prometheus/api/v1/export
       - /prometheus/api/v1/export/native
       - /prometheus/api/v1/labels
       - /prometheus/api/v1/label/.*/values
       - /prometheus/api/v1/query
       - /prometheus/api/v1/query_range
       - /prometheus/api/v1/series
       - /prometheus/api/v1/status/.*
       - /prometheus/federate
       - /prometheus/vmui/.*
       - /api/v1/status/.*
       - /vmui
       - /vmui/.*
   

   Remember to replace your-namespace with your actual namespace.

2. Deploy the VMUser: Apply the YAML configuration to your Kubernetes cluster.

3. Access VMUI: Point your browser to your VMAuth endpoint (e.g., https://vmauth/vmui/) and log in with the credentials defined in the VMUser (in this case, testuser:testpass).

4. Attempt a Query or Open Cardinality Explorer: Try running a query or navigating to the cardinality explorer. If you're running a version of VictoriaMetrics v1.125.0 or later, you'll likely encounter errors.

5. Observe the Network Requests: Use your browser's developer tools to inspect the network requests. You'll notice that the requests are being made to incorrect URLs (e.g., /api/v1/status instead of /prometheus/api/v1/status).

By following these steps, you can reliably reproduce the bug and confirm its presence in your environment.

Analyzing Logs and Screenshots: Evidence of the Bug

The bug report includes valuable visual evidence in the form of screenshots, which clearly demonstrate the difference in network requests before and after version v1.125.0. Let's analyze these screenshots:

• Before v1.125.0: The screenshot shows that the requests are correctly routed to endpoints under the /prometheus path, such as /prometheus/api/v1/status. This indicates that VMUI is correctly constructing URLs with the necessary prefix.
• After v1.125.0: The screenshot reveals that the requests are now being sent to endpoints without the /prometheus prefix, such as /api/v1/status. This confirms that VMUI is failing to include the required prefix in the URLs.

This visual comparison provides compelling evidence of the bug and its impact on VMUI's functionality. The logs, while not explicitly provided in the bug report, would likely further corroborate this issue by showing 404 errors or other indications of failed requests to the incorrect endpoints.

Impact and Solutions: Addressing the URL Guessing Issue

The impact of this bug extends beyond mere inconvenience. In multi-tenant environments, where access control and data isolation are paramount, this issue can have serious consequences. Incorrectly routed requests can lead to data access violations, security vulnerabilities, and operational disruptions.

Fortunately, the VictoriaMetrics team is actively addressing this issue. While a specific fix or workaround isn't explicitly mentioned in the provided information, here are some general strategies that can be employed to mitigate the problem:

1. Upgrade to the Latest Version: The VictoriaMetrics team is likely aware of this bug and may have already released a fix in a later version. Upgrading to the latest stable release is always a good first step.
2. Check Release Notes: Review the release notes for versions later than v1.125.0 to see if the bug is explicitly mentioned and if a fix is included.
3. Monitor the Issue Tracker: Keep an eye on the VictoriaMetrics issue tracker (e.g., GitHub issues) for updates and discussions related to this bug. You may find workarounds or temporary solutions posted by other users or the developers themselves.
4. Implement a Reverse Proxy Workaround: As a temporary measure, you could potentially configure a reverse proxy to rewrite the incorrect URLs generated by VMUI. This would involve intercepting requests to /api/v1/status and rewriting them to /prometheus/api/v1/status.
5. Revert to a Previous Version: If upgrading isn't immediately feasible, you could consider temporarily reverting to a version prior to v1.125.0 where this bug wasn't present. However, be aware that this may also reintroduce other bugs or security vulnerabilities that have been fixed in later versions.

It's crucial to carefully evaluate the impact of this bug on your specific environment and choose the most appropriate solution based on your needs and constraints. If you're experiencing this issue, it's highly recommended to engage with the VictoriaMetrics community and support channels to seek guidance and share your experience.

Conclusion: Staying Informed and Proactive

The case of VMUI guessing wrong URLs when using target_path_suffix highlights the importance of staying informed about potential bugs and proactively addressing them. By understanding the underlying issue, its impact, and available solutions, you can ensure the stability and security of your VictoriaMetrics deployment.

Remember to always keep your monitoring tools up to date, monitor issue trackers for known bugs, and engage with the community to share your experiences and learn from others. By working together, we can ensure the continued reliability and effectiveness of monitoring solutions like VictoriaMetrics.

For further information and updates on VictoriaMetrics, you can visit their official website and documentation. You might also find helpful resources and discussions on platforms like the VictoriaMetrics GitHub repository, where you can track issues, contribute to the project, and engage with the community.