Running Spring Boot Microservices using Docker and AWS ECS

I am developing a simple micro-service based application using Spring Boot, Kafka & MongoDB.

There are 4 Spring Boot based REST services that performs CRUD on MongoDB(shared between all services for now) and publish/poll messages to/from Kafka cluster.

Currently I have them all deployed on hand crafted AWS EC2 instances. Kafka/Zookeeper has 3 brokers/instances. MongoDb with no replication/sharding.

What do I want to achieve ?

• Run the micro-services in docker containers managed by ECS.
• Ability to scale out these services.
• Ability to create dedicated environment(DEV, QA, UAT, PROD) on ECS.
• Run Kafka and MongoDB cluster with replication and sharding as containers managed by ECS.

I am fairly new to Docker & ECS concepts as such and not able to find exactly how is it done. I am able to create Dockerfile, image and push to docker hub and use one of the service ( that has no external dependencies ) on ECS. One of the Dockerfile looks like this:-

FROM openjdk:8-jre-alpine
EXPOSE 443 443
LABEL "author":"Kumar Sambhav Jain"
COPY build/distributions/app.tar /opt/app/
RUN tar -xvf /opt/app/admin.tar -C /opt/app/
WORKDIR /opt/app/admin/bin
ENTRYPOINT ["./admin"]

Questions:-

1. What is ideal or right way to deploy the whole application ? Do I need ECS cluster per environment (DEV, QA, UAT) or ECS cluster per service type - two services need to be publicly exposed on port 443/80.
2. How do the service connect to MongoDB and Kafka running in containers ? Currently Kafka broker and mongo connection are maintained in application.yml files like this:-

spring:
  data:
    mongodb:
      host: 172.31.18.25
      database: abcd
      username: test
      password: abcd@123
  cloud:
    stream:
      kafka:
        binder:
          zk-nodes:
          - 172.31.18.58:2181
          - 172.31.28.201:2181
          - 172.31.25.60:2181
          brokers:
          - 172.31.18.58:9092
          - 172.31.28.201:9092
          - 172.31.25.60:9092

How does it change once everything is containerized ?

Reference to any study material on this exact topic.