Elastic URL should be updated with Elastic LoadBalancer service in multi node environments post installation.
You can find below the manual steps. We are planning to automate this process in 21.3.2 (DE517399)
DX Platform 20.2.x and 21.3.1
For DX OI
https://knowledge.broadcom.com/external/article/226230
For DX AXA, BPA and Kibana
https://knowledge.broadcom.com/external/article/226133
For DX APM
https://knowledge.broadcom.com/external/article/226139
For DX Dashboards
https://knowledge.broadcom.com/external/article/225604