How do I troubleshoot an inaccessible ZCenter page or API after enabling HTTPS?

Issue/Introduction

This article describes how to troubleshoot an inaccessible ZCenter page, an API that returns 502/503, a browser certificate error, or a certificate that is not updated after HTTPS is enabled or an SSL certificate is uploaded. After ZCenter saves sslSetting, it asynchronously notifies Base through RabbitMQ to update Caddy. A successful save does not mean that Caddy loaded the configuration successfully.

Symptoms

• After HTTPS is enabled, the browser cannot connect, the TLS handshake fails, or an incorrect certificate is returned.
• The certificate upload API succeeds, but access still presents the old or built-in certificate.
• The HTTP endpoint works but the HTTPS endpoint does not, or the setting shows HTTPS as enabled while Caddy still listens in HTTP mode.
• Base or Caddy logs contain errors related to certificate loading, the Caddy admin API, MQ message consumption, or port listening.

Environment

• Product: ZCenter
• Version: 5.1.0
• Component: Portal global settings, Base, RabbitMQ, Caddy, and SSL certificates

Possible causes

• sslSetting has been written to the database, but the RabbitMQ refresh event was not sent or consumed successfully.