Spring boot unable to connect to elasticsearch docker

My Elasticsearch docker-compose file is as such

version: '3'

services:
  elasticsearch:
    image: docker.elastic.co/elasticsearch/elasticsearch:6.8.6
    container_name: elasticsearch
    environment:
      - cluster.name=cluster
      - bootstrap.memory_lock=true
      - "ES_JAVA_OPTS=-Xms512m -Xmx512m"
    ulimits:
      memlock:
        soft: -1
        hard: -1
    volumes:
      - ./config/elasticsearch/elasticsearch.yml:/usr/share/elasticsearch/elasticsearch.yml
      - esdata6:/usr/share/elasticsearch/data    
    ports:
      - "9200:9200"
  kibana:
    image: docker.elastic.co/kibana/kibana:6.8.6
    container_name: kibana
    volumes:
      - ./config/kibana/kibana.yml:/usr/share/kibana/kibana.yml
    restart: on-failure
    ports:
      - "5601:5601"

volumes:
  esdata6:

I have a spring boot application and the application.properties is

spring.data.elasticsearch.repositories.enabled=true
spring.data.elasticsearch.cluster-nodes=localhost:9200
spring.data.elasticsearch.cluster-name=cluster

However, I am getting the error

2020-04-18 13:49:45.775  INFO 7576 --- [           main] o.s.d.e.c.TransportClientFactoryBean     : Adding transport node : 127.0.0.1:9200
2020-04-18 13:50:16.961 ERROR 7576 --- [           main] .d.e.r.s.AbstractElasticsearchRepository : failed to load elasticsearch nodes : org.elasticsearch.client.transport.NoNodeAvailableException: None of the configured nodes are available: [{#transport#-1}{Lzoi5ddvSJizvu4g3Y3E6Q}{localhost}{127.0.0.1:9200}]

Question:
1) How can i connect to the elasticsearch with spring boot externally?
2) If I docker-compose up the elastic and the springboot application together, they would be on the same network. What change should I ammend to spring.data.elasticsearch.cluster-nodes in order to connect to the elastic search?

I am using spring-boot-starter-data-elasticsearch in the spring boot app.

Source: StackOverflow