{ISILON} 8.0+ Cannot use the OneFS Web Interface due to " server-side failure with status code 500" error

When trying to access the OneFS Web Interface, you will face the " server-side failure with status code 500" on the login screen as seen below: 


you will not be able to login to the web interface when you face this error. 

Right click on the web-page -> select Inspect (Inspect Element if you're using Mozilla Firefox) and navigate to the "Network" tab.
Inspecting the web page from the network tab shows that the /platform/1/cluster/identity information could not be fetched by the papi resulting in a "503: service not available" error : 

This can happen if the apache2 server is not able to communicate properly with the isi_papi_d service.

We will have to verify that the isi_papi_d service is running properly. 

1. check if the isi_papi_d service is enabled : 

# isi services -a isi_papi_d

2. if the isi_papi_d service is disabled, enable it by running the following command : 

# isi services -a isi_papi_d
Service 'isi_papi_d' is enabled.

3. if the isi_papi_d service was already enabled, check the /var/log/apache2/webui_httpd_error.log for errors such as this : 

2018-09-24T11:47:56Z <18.3> PDC-NAS-ISN01-20 httpd[80131]: [:error] [pid 80131:tid 34676253696] (20)Not a directory: [client 192.168.10.10:37994] FastCGI: failed to connect to server "/usr/sbin/isi_papi_d": socket file descriptor (1712) is larger than FD_SETSIZE (1024), you probably need to rebuild Apache with a larger FD_SETSIZE
2018-09-24T11:47:56Z <18.3> PDC-NAS-ISN01-20 httpd[80131]: [:error] [pid 80131:tid 34676253696] [client 10.0.2.63:37994] FastCGI: incomplete headers (0 bytes) received from server "/usr/sbin/isi_papi_d"
2018-09-24T11:47:56Z <18.3> PDC-NAS-ISN01-20 httpd[80131]: [:error] [pid 80131:tid 34676253696] [client 10.0.2.63:37994] FastCGI: do_work() failed with ret 500 for request GET /platform/1/cluster/config HTTP/1.1

if you see the above error, you should restart the isi_papi_d service by running the below commands : 

# isi services -a isi_papi_d disable

# isi services -a isi_papi_d enable

After the service is restarted, you should be able to login to the Web Interface. If you still face the issue after/during restarting isi_papi_d, please contact Isilon Support.