In this article, we will troubleshoot the JavaConnectException: Connection Refused issue that occurs when starting up a Spring Boot service in a Docker Compose file. Specifically, we will focus on a use case where one of the services acts as an OAuth client and fails to start.
Context
Docker Compose is a popular tool for defining and running multi-container Docker applications. It allows you to define a docker-compose.yml file that specifies the services, networks, and volumes required for your application. Spring Boot is a popular Java framework for building microservices, and it can be easily containerized using Docker.
OAuth is an authorization protocol that enables third-party services to access resources on behalf of a user. Keycloak is an open-source identity and access management solution that can be used as an OAuth server. In our use case, we have a few Spring Boot services that need to access resources from each other, and we will use Keycloak as the OAuth server.
Problem
When we start up our Docker Compose file, we encounter the following error:
Caused by: org.springframework.web.client.ResourceAccessException: I/O error on GET request for "http://keycloak:8080/auth/realms/master/protocol/openid-connect/token": Connect to keycloak:8080 [keycloak/172.18.0.3] failed: Connection refused (Connection refused); nested exception is java.net.ConnectException: Connect to keycloak:8080 [keycloak/172.18.0.3] failed: Connection refused (Connection refused)This error occurs because the Spring Boot service that acts as the OAuth client cannot connect to the Keycloak server at http://keycloak:8080/auth/realms/master/protocol/openid-connect/token.
Troubleshooting
Check Docker Compose Logs
The first step in troubleshooting this issue is to check the Docker Compose logs for any errors or warnings. You can do this by running the following command:
docker-compose logsThis command will show you the logs for all the services defined in your docker-compose.yml file. Look for any errors or warnings that might indicate a problem with the Keycloak server or the OAuth client service.
Check Network Connectivity
If the Docker Compose logs do not reveal any issues, the next step is to check the network connectivity between the OAuth client service and the Keycloak server. You can do this by running the following command:
docker network inspect Replace docker-compose.yml file. This command will show you the details of the network, including the IP addresses of the containers.
Next, use the following command to test the connectivity from the OAuth client service to the Keycloak server:
docker exec ping keycloak Replace
Check Keycloak Configuration
If the network connectivity is fine, the next step is to check the Keycloak configuration. Ensure that the Keycloak server is running and that the OAuth client is registered in Keycloak with the correct configuration.
Check the Keycloak logs for any errors or warnings. You can do this by running the following command:
docker-compose logs keycloakCheck OAuth Client Configuration
If the Keycloak configuration is fine, the next step is to check the OAuth client configuration. Ensure that the OAuth client is configured with the correct Keycloak endpoint and that the client credentials are correct.
Reproduce the Issue
If none of the above steps help, try to reproduce the issue manually. Start the Keycloak server and the OAuth client service individually and try to reproduce the error.
Key Concepts
JavaConnectException: An exception that indicates a problem with connecting to a remote server.ConnectionRefused: An error that occurs when a remote server refuses a connection request.- Docker Compose: A tool for defining and running multi-container Docker applications.
- Spring Boot: A popular Java framework for building microservices.
- OAuth: An authorization protocol that enables third-party services to access resources on behalf of a user.
- Keycloak: An open-source identity and access management solution.
In this article, we covered the steps for troubleshooting the JavaConnectException: Connection Refused issue that occurs when starting up a Spring Boot service in a Docker Compose file. We focused on a use case where one of the services acts as an OAuth client and fails to start and covered the key concepts related to the issue.