Target.ResponseCodeMismatch Error on Application Load Balancer of WordPress Deployed in Elastic Beanstalk

The error message "Target.ResponseCodeMismatch" indicates that the health check response from your target (in this case, your WordPress application) did not match the expected HTTP response code(s) configured in your Application Load Balancer's health check settings.

Here are some steps you can take to troubleshoot and resolve this issue:

• Check the Health Check Configuration: Ensure that the health check path is correct and the expected status code is set properly. For a WordPress application, the health check path is typically set to the root ("/") or to a specific page that you know exists (like "/wp-admin"). The expected status code is usually "200".
• Check the Application's Response: You can manually check the response code of your application by sending a request to the health check URL from the instance itself or another instance in the same VPC. You can do this using curl or another similar tool. For example: curl -I http://localhost/wordpress/. The response code should match the one expected by the health check.
• Check the Security Group and Network ACLs: Ensure that your security group and network ACLs allow inbound traffic on the port your application is listening on (usually port 80 for HTTP or 443 for HTTPS).
• Check the Application Logs: Check the logs of your WordPress application to see if there are any errors that could be causing the health check to fail.
• Check the Load Balancer Logs: Enable access logs for your Application Load Balancer to get more information about the health check requests and responses.

If none of these steps resolve the issue, it might be a more specific issue with your WordPress configuration or your Elastic Beanstalk environment. In that case, you might need to dig deeper into the application logs.