Understanding DecK and Kong

Oct 13, 2025 by wbrum.org 129 views

Introduction

When working with declarative configurations for Kong using DecK, it's essential to understand how DecK handles upstream targets. In this article, we'll explore a common issue where DecK identifies all targets as new and recreates them, resulting in a UNIQUE violation during the sync process. We'll delve into the possible reasons behind this behavior and discuss potential solutions to ensure unique targets.

Understanding DecK and Kong

DecK is a declarative configuration tool for Kong, allowing you to manage your Kong configuration in a YAML file. This approach simplifies the process of managing complex configurations and ensures consistency across your environment. Kong, on the other hand, is a popular open-source API gateway that provides a robust set of features for managing APIs.

The Issue: UNIQUE Violation

When using deck gateway sync to keep your declarative Kong config in sync with your gateway, you may encounter a UNIQUE violation error. This error occurs when DecK attempts to create a target that already exists, resulting in a conflict. The error message typically indicates that a UNIQUE violation has been detected on the target.

Example Use Case

Let's consider an example configuration file that defines an upstream with targets:

_format_version: "1.1"

upstreams:
  - name: example
    targets:
    - target: www.google.com

When you run deck gateway sync ./config/*.yaml, DecK will attempt to create the target www.google.com for the upstream. However, if the target already exists, DecK will identify it as new and recreate it, resulting in a UNIQUE violation error.

Debugging the Issue

To troubleshoot this issue, you can examine the output of the deck gateway sync command. The error message will typically indicate the specific target that caused the UNIQUE violation. In the example above, the error message suggests that the target www.google.com:8000 is the culprit.

Possible Solutions

There are a few possible solutions to this issue:

1. Use a Unique Target Name

One possible solution is to use a unique target name that doesn't conflict with existing targets. For example, you can append a suffix to the target name, such as www.google.com:8001.

2. Specify the Target Port

Another solution is to specify the target port explicitly, as shown in the example above. This ensures that DecK creates the target with the correct port number, avoiding conflicts with existing targets.

3. Use a Different Upstream Name

If you're using the same upstream name for multiple targets, you may need to use a different upstream name to avoid conflicts. This can be achieved by creating a new upstream with a unique name and specifying the target accordingly.

4. Disable Unique Constraint

As a last resort, you can disable the unique constraint on the target by setting the unique field to false in your configuration file. However, this approach is not recommended, as it may lead to data inconsistencies and other issues.

Conclusion

In conclusion, the UNIQUE violation error when creating existing targets for upstream is a common issue that can be resolved by using a unique target name, specifying the target port, using a different upstream name, or disabling the unique constraint. By understanding the possible causes and solutions to this issue, you can ensure a smooth and efficient configuration management process using DecK and Kong.

Best Practices

To avoid this issue in the future, follow these best practices:

Use unique target names to avoid conflicts with existing targets.
Specify the target port explicitly to ensure correct port numbers.
Use a different upstream name for multiple targets to avoid conflicts.
Regularly review and update your configuration files to ensure consistency and accuracy.

Introduction

In our previous article, we explored the issue of UNIQUE violation errors when creating existing targets for upstream using DecK and Kong. We discussed possible solutions to this issue and provided best practices for avoiding it in the future. In this article, we'll answer some frequently asked questions (FAQs) related to this issue.

Q: What is a UNIQUE violation error?

A: A UNIQUE violation error occurs when DecK attempts to create a target that already exists, resulting in a conflict. This error is typically indicated by a message stating that a UNIQUE violation has been detected on the target.

Q: Why does DecK identify all targets as new and recreate them?

A: DecK identifies all targets as new and recreates them because it doesn't have any information about the existing targets. This is a known issue with DecK, and it's being addressed in future releases.

Q: How can I avoid UNIQUE violation errors?

A: To avoid UNIQUE violation errors, you can use a unique target name, specify the target port explicitly, use a different upstream name, or disable the unique constraint. We discussed these solutions in our previous article.

Q: What is the difference between a target and an upstream?

A: A target is a specific endpoint that is being proxied by the upstream, while an upstream is a group of targets that are being proxied together. In other words, an upstream is a collection of targets.

Q: Can I use the same upstream name for multiple targets?

A: No, you cannot use the same upstream name for multiple targets. This will result in a UNIQUE violation error. Instead, you should use a different upstream name for each group of targets.

Q: How can I specify the target port explicitly?

A: You can specify the target port explicitly by including the port number in the target name, as shown in the example below:

_format_version: "1.1"

upstreams:
  - name: example
    targets:
    - target: www.google.com:8000

Q: What is the `unique` field in the configuration file?

A: The unique field in the configuration file specifies whether the target should be unique or not. If set to true, DecK will ensure that the target is unique. If set to false, DecK will not enforce uniqueness.

Q: Can I disable the unique constraint on the target?

A: Yes, you can disable the unique constraint on the target by setting the unique field to false in your configuration file. However, this approach is not recommended, as it may lead to data inconsistencies and other issues.

Q: How can I troubleshoot UNIQUE violation errors?

A: To troubleshoot UNIQUE violation errors, you can examine the output of the deck gateway sync command. The error message will typically indicate the specific target that caused the UNIQUE violation.

Conclusion

In conclusion, UNIQUE violation errors when creating existing targets for upstream are a common issue that can be resolved by using a unique target name, specifying the target port explicitly, using a different upstream name, or disabling the unique constraint. By understanding the possible causes and solutions to this issue, you can ensure a smooth and efficient configuration management process using DecK and Kong.

Best Practices

To avoid UNIQUE violation errors in the future, follow these best practices:

Use unique target names to avoid conflicts with existing targets.
Specify the target port explicitly to ensure correct port numbers.
Use a different upstream name for multiple targets to avoid conflicts.
Regularly review and update your configuration files to ensure consistency and accuracy.

By following these best practices and understanding the possible solutions to the UNIQUE violation error, you can ensure a seamless configuration management process using DecK and Kong.