Cannot access from APICast on OpenShift to 3scale admin endpoint

Issue

• When I installed 3scale 2.1, apicast-production pod failed in starting. The error message is the below.

2018/04/16 06:16:15 [debug] 1#1: [lua] util.lua:40: system(): os execute cd '/opt/app-root/src/' && libexec/boot
2018/04/16 06:16:15 [debug] 1#1: [lua] env.lua:59: fetch(): env: THREESCALE_CONFIG_FILE = nil
2018/04/16 06:16:15 [emerg] 1#1: [lua] configuration_loader.lua:122: init(): failed to load configuration, exiting (code 1)
2018/04/16 06:16:15 [warn] 29#29: *2 [lua] remote_v2.lua:161: call(): failed to get list of services: invalid status: 403 (Forbidden) url: http://system-provider:3000/admin/api/services.json , context: ngx.timer
./src/configuration_loader.lua:47: missing configuration
stack traceback:
    ./src/configuration_loader.lua:47: in function 'boot'
    libexec/boot.lua:6: in function 'file_gen'
    init_worker_by_lua:38: in function <init_worker_by_lua:36>
    [C]: in function 'xpcall'
    init_worker_by_lua:45: in function <init_worker_by_lua:43>

I've configured THREESCALE_PORTAL_ENDPOINT environment variable.