Example of docker-compose for keycloak 18 with ability to import a realm file:

It assumes the realm-export.json file is in /PATH_OF_realm-export.json_FILE/

docker-compose.yml:

version: '3'
services:
    keycloak:
        image: 'quay.io/keycloak/keycloak:18.0.2'
        container_name: keycloak
        command: [ 'start-dev --import-realm' ]
        environment:
            - KEYCLOAK_DB=dev-file
            - KEYCLOAK_ADMIN=admin
            - KEYCLOAK_ADMIN_PASSWORD=admin
            - KEYCLOAK_FEATURES=scripts
            - KEYCLOAK_HTTP_PORT=8080
        volumes:
            - /PATH_OF_realm-export.json_FILE/:/opt/keycloak/data/import
        ports:
            - 8082:8080