Unable to access Management UIs

If you are unable to access the UI login page, getting a blank page, an HTTP 404, or some other error.

When this happens it means that either the Management subsystem is down, or the access attempt is not reaching the Management subsystem due to a problem in the environment.

Check the following:

Is the access attempt actually reaching the Management subsystem? To confirm this, check what is in the logs of the juhu pods which run on the Management subsystem. The juhu pods are the entry point for all UI, REST, and CLI requests to the Management subsystem. For every access request there should be line logged by the juhupod, for example: When the user attempts to access the admin UI login page, the following is logged by the juhu pod:
```
kubectl logs abc-management-juhu-fc8f6bb5d-jnw2q --since=5m
...
9.20.85.205 - - [27/May/2022:10:35:49 +0000] [675fa59030a1a68028712ad2fdb2fdb1] "GET /api/cloud/admin/identity-providers HTTP/1.1" 200 301 "https://apimsvc20.hursley.ibm.com/auth/admin/sign-in/" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/101.0.4951.64 Safari/537.36" "9.145.13.216" [127.0.0.1:2000] request_time=0.222 upstream_response_time=0.224
...
```
Note that the timestamp of these log records are not the time when the request arrived, but the time when the response to the request was sent back. To work out the arrival time you can subtract the request_time=0.222 that appears later in the log message. If there is nothing logged in the juhu pods at the time the UI access is attempted, then check if you have any network problems between your browser and the Management subsystem.
Are the Management subsystem pods all up and running? Check this with kubectl get ManagementCluster -n <namespace>. If this does not show all pods running, then check which pods are failing: kubectl get pods -n <namespace>. Otherwise it's worth checking the reasons why the pods are failing to start with kubectl describe as it might be something in your kubernetes environment that you can fix. Note that on the Management subsystem the postgres pods will need to be running first, so if these are not running then most other Management pods will not start.
Check the logs of the apim pods while attempting to access the UI. The juhu pods receive the requests from the UI, and send them on to the apim pods for processing. The logs of the apim pods may reveal some clues as to the cause of the problem. If nothing is logged in the apim pods at the time of the access attempt then it suggests a problem in the environment, the juhu pods unable to forward requests to apim.