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Discover how to configure external YAML files for your Spring Boot application when running from a JAR, ensuring Liquibase migrations function seamlessly.
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Accessing External Configuration Files in Spring Boot JAR Execution

Running a Spring Boot application from a JAR file provides a convenient method for deploying applications. However, there are challenges when it comes to managing configuration files, especially when you need to utilize an external YAML configuration that persists across different environments. This post addresses a common concern: How can you enable an external configuration file when executing a Spring Boot JAR, specifically for Liquibase migrations?

The Challenge

In Spring Boot applications, especially those using different profiles (like application-{profile}.yml), configuration management can get tricky, particularly in production environments. Here's the scenario:

You have a Spring Boot application using Liquibase for automatic database migrations.

You need to pass an external configuration file (application-prod.yml) at runtime from a different location.

However, Liquibase looks for changelog files using the classpath, resulting in a failure when these files are not accessible.

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This leads to Liquibase not being able to locate the necessary changelog files specified with:

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The Solution

To solve this issue effectively, we can separate the configuration into two files. Here's how you can implement it:

Step 1: Separate Configuration Files

Keep a Base Configuration File:

Store the application-prod.yml in the ./src/main/resources directory. This means it will be packed within the JAR and accessible for classpath resources.

Create a Custom Configuration File:

Create a separate YAML file (e.g., application-customization.yml) that will reside outside of the JAR file in the same directory from which you run your application. This file can be used to override or add specific settings, like database connections and authorization server configurations.

Step 2: Update application-prod.yml

In your packed application-prod.yml, include the application-customization.yml as shown below:

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This will allow Spring Boot to recognize the external custom configuration alongside the internally packed configuration file.

Step 3: Validate Liquibase Configuration

Ensure your changelog configuration in application-prod.yml points correctly to where Liquibase can access it:

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Conclusion

By structuring your configuration files appropriately, you can ensure that your Spring Boot application accesses both external and internal configurations seamlessly. Using application-prod.yml to include an external file like application-customization.yml allows you to keep your external configurations flexible and your changelog accessible, making Liquibase work efficiently in your production environment.

If you follow these steps, you'll eliminate the challenge of running Liquibase migrations with an external configuration file while deploying your Spring Boot application.

For more insights and tips on Spring Boot configuration management, feel free to explore our other guides!