Solving the “Connection refused to Keycloak’s configuration URI” Conundrum in Spring Boot and Docker

Are you tired of staring at the “Connection refused to Keycloak’s configuration URI” error message, wondering why your Spring Boot service can’t seem to connect to your Keycloak instance, both of which are running happily in their respective Docker containers? Well, wonder no more! In this article, we’ll dive into the world of containerized authentication and explore the possible causes and solutions to this frustrating issue.

Prerequisites

Before we begin, make sure you have the following setup:

• Keycloak installed and running in a Docker container
• A Spring Boot service configured to use Keycloak for authentication, also running in a Docker container
• A basic understanding of Docker, Spring Boot, and Keycloak

Understanding the Error

The “Connection refused to Keycloak’s configuration URI” error typically occurs when your Spring Boot service attempts to connect to Keycloak’s configuration URI (usually http://keycloak:8080/auth/realms/{realm}/.well-known/openid-configuration) and fails. This can happen due to various reasons, which we’ll explore in the following sections.

Reason 1: Misconfigured Keycloak URL

One of the most common causes of this error is a misconfigured Keycloak URL in your Spring Boot service. Double-check that your application.properties or application.yml file contains the correct Keycloak URL:

keycloak:
  auth-server-url: http://keycloak:8080/auth

Make sure the URL matches the one you used to start the Keycloak container. If you’re using a custom domain or port, update the URL accordingly.

Reason 2: Docker Networking Issues

When running multiple containers, Docker uses a bridge network to connect them. However, this network is not enabled by default. You need to create a Docker network and attach both containers to it:

docker network create my-network
docker run -d --name keycloak --network=my-network keycloak
docker run -d --name spring-boot --network=my-network spring-boot

This ensures that both containers can communicate with each other using their container names as hostnames.

Reason 3: Firewall or Proxy Interference

Frequently, firewalls or proxies can block the connection between your Spring Boot service and Keycloak. Check if you have any firewall rules or proxies that might be interfering with the connection:

docker exec -it spring-boot iptables -L

If you find any rules that might be blocking the connection, update or remove them accordingly.

Reason 4: Keycloak Not Ready or Available

When starting Keycloak in a Docker container, it might take some time to become available. Your Spring Boot service might be trying to connect to Keycloak before it’s fully initialized:

docker run -d --name keycloak -p 8080:8080 keycloak
sleep 10
docker run -d --name spring-boot spring-boot

Use the sleep command to delay the startup of your Spring Boot service, allowing Keycloak to fully initialize before attempting to connect.

Reason 5: Missing or Incorrect Dependencies

Verify that your Spring Boot project has the necessary dependencies to connect to Keycloak:

In your pom.xml file (if you’re using Maven):

<dependency>
    <groupId>org.keycloak</groupId>
    <artifactId>keycloak-spring-boot-starter</artifactId>
</dependency>

In your build.gradle file (if you’re using Gradle):

dependencies {
    implementation 'org.keycloak:keycloak-spring-boot-starter'
}

Troubleshooting Steps

Follow these steps to troubleshoot the issue:

1. Check the Keycloak URL in your application.properties or application.yml file and ensure it matches the one used to start the Keycloak container.
2. Verify that both containers are attached to the same Docker network.
3. Inspect the Docker logs for any error messages using docker logs -f keycloak and docker logs -f spring-boot.
4. Check if any firewall rules or proxies are blocking the connection.
5. Delay the startup of your Spring Boot service to ensure Keycloak has time to initialize.
6. Verify that your Spring Boot project has the necessary dependencies to connect to Keycloak.

Conclusion

Solving the “Connection refused to Keycloak’s configuration URI” error requires a thorough understanding of the possible causes and a methodical approach to troubleshooting. By following the steps outlined in this article, you should be able to identify and resolve the issue, ensuring seamless communication between your Spring Boot service and Keycloak instance, both running in their respective Docker containers.

Cause	Solution
Misconfigured Keycloak URL	Update the Keycloak URL in application.properties or application.yml
Docker Networking Issues	Create a Docker network and attach both containers to it
Firewall or Proxy Interference	Check and update firewall rules or proxies
Keycloak Not Ready or Available	Delay the startup of the Spring Boot service using the sleep command
Missing or Incorrect Dependencies	Verify and update dependencies in the Spring Boot project

By following this comprehensive guide, you’ll be well on your way to resolving the “Connection refused to Keycloak’s configuration URI” error and enjoying a smooth, secure authentication experience with your Spring Boot service and Keycloak instance.

Bonus: Advanced Troubleshooting Techniques

If you’re still struggling to resolve the issue, consider using the following advanced troubleshooting techniques:

• Use Docker’s built-in debugging tools, such as docker inspect and docker logs, to gather more information about the containers and their configurations.
• Enable debug logging in your Spring Boot application to get more detailed error messages.
• Use a tool like curl or wget to test the connection to Keycloak’s configuration URI from within the Spring Boot container.

By combining these techniques with the solutions outlined in this article, you’ll be well-equipped to tackle even the most stubborn “Connection refused to Keycloak’s configuration URI” errors.

Frequently Asked Question

Get answers to the most frequently asked questions about Keycloak configuration URI connection issues from a Spring Boot gateway service, both running on Docker.