Failed ping error running inside container

[rocktz]

Hello
I am trying to run 2 instance of my service (on RockyLinux) which uses memberlist for discovery (using DefaultWANConfig() )
The cluster starts, add the member but then drop the node.

Here is my docker-compose file relevant extract

version: "3.9"

networks:
  backend-network:
    driver: bridge

services:
  calendar-1:
    ports:
      - "9998:9999"
    environment:
      - BOTNET_MEMBERLIST_ADVERTISE_ADDRESS=${HOST_MACHINE_IP}:9998
      - BOTNET_MEMBERLIST_BIND_ADDRESS=0.0.0.0:9999
      - BOTNET_MEMBERLIST_KNOWN_NODES=
  calendar-2:
    depends_on:
      - calendar-1
    networks:
      - backend-network
    ports:
      - "9997:9999"
    environment:
      - BOTNET_MEMBERLIST_ADVERTISE_ADDRESS=${HOST_MACHINE_IP}:9997
      - BOTNET_MEMBERLIST_BIND_ADDRESS=0.0.0.0:9999
      - BOTNET_MEMBERLIST_KNOWN_NODES=${HOST_MACHINE_IP}:9998

where
HOST_MACHINE_IP =public ip of the host