Connection refused when connecting to keycloak container from backend container

I have two containers backend (spring boot application) and Keycloak. if I run keycloak in a container and backend locally : it works

If both of them are run in container the backend doesn't start and shows the following error :

Failed to instantiate [org.springframework.security.oauth2.jwt.JwtDecoder]: Factory method 'jwtDecoderByIssuerUri' threw exception; nested exception is java.lang.IllegalArgumentException: Unable to resolve the Configuration with the provided Issuer of "http://keycloak:8082/auth/realms/myrealm"

Caused by: org.springframework.web.client.ResourceAccessException: I/O error on GET request for "http://keycloak:8082/auth/realms/myrealm/.well-known/openid-configuration": Connection refused (Connection refused); 

following are my configs :

docker-compose :

services:

  keycloak:
    image: jboss/keycloak:8.0.1
    command:
      - " -b 0.0.0.0"
    container_name: "keycloak"
    networks:
      - myproject
    volumes:
      - "./keycloak/realm-export.json:/opt/jboss/keycloak/bin/keycloak_export_dir/realm-export.json"
    environment:
      KEYCLOAK_USER: admin
      KEYCLOAK_PASSWORD: admin
      KEYCLOAK_IMPORT: /opt/jboss/keycloak/bin/keycloak_export_dir/realm-export.json
    ports:
      - "8082:8080"

  backend:
    build:
      context: ./backend
      dockerfile: Dockerfile
    container_name: "backend"
    environment:
      - spring.oauth2.resourceserver.jwt.issuer-uri= http://keycloak:8082/auth/realms/myrealm
    links:
      - keycloak
    networks:
      - myproject
    restart: on-failure
    ports:
      - "8080:8080"

networks:
  myproject:
    driver: bridge

application.yml:

  application:
    name: backend
  security:
    oauth2:
      resourceserver:
        jwt:
          issuer-uri: http://localhost:8082/auth/realms/myrealm

do you have any Idea why do I get connection refused ? any help is appreciated :)