Cannot access the Multi-Cluster Manager user interface

Resolve issues accessing the Multi-Cluster Manager user interface over HTTPS.

Problem

The browser shows a connection error or cannot load the Multi-Cluster Manager UI.

Explanation

The UI is served through an HTTPS-enabled nginx service. UI access failures typically occur when the UI service is stopped, required ports are blocked, or the HTTPS endpoint is unreachable.

Resolution

Verify that the HTTPS endpoint responds.
```
curl -k -I https://LOCALHOST
```
Expected output includes an HTTP status code of 200 OK.
Verify that the UI service is running.
```
systemctl status ui.service
```
If the service is not running, review the logs.
- ```
tail /var/logs/mcm/ui/access.log -f
```
- ```
tail /var/logs/mcm/ui/error.log -f
```
Restart the service, if required.
Verify that ports 80 and 443 are listening.
```
ss -tulpn
```
The source documentation maps port 443 to the UI HTTPS service.