Test setup with 3 cassandra nodes in a cluster and a client container

cassandra_3_nodes_docker-compose.yaml

version: '2'

services:
  cassandra-1:
    image: cassandra:2
    environment:
      - CASSANDRA_CLUSTER_NAME="demo_3nodes"
      - CASSANDRA_BROADCAST_ADDRESS=cassandra-1
    ports:
      - "9042:9042"
      - "7000:7000"

  cassandra-2:
    image: cassandra:2
    depends_on:
      - cassandra-1
    environment:
      - CASSANDRA_CLUSTER_NAME="demo_3nodes"
      - CASSANDRA_SEEDS=cassandra-1
      - CASSANDRA_BROADCAST_ADDRESS=cassandra-2
    ports:
      - "9043:9042"
    restart: always

  cassandra-3:
    image: cassandra:2
    depends_on:
      - cassandra-1
    environment:
      - CASSANDRA_CLUSTER_NAME="demo_3nodes"
      - CASSANDRA_SEEDS=cassandra-1
      - CASSANDRA_BROADCAST_ADDRESS=cassandra-3
    ports:
      - "9044:9042"
    restart: always

  cassandra_cqlsh:
    image: cassandra:2
    environment:
      - CASSANDRA_CLUSTER_NAME="demo_3nodes"
    command: sh -c "cqlsh cassandra-1"

First start the cassandra-1 node and once it the DB is running, start up cassandra-2 and cassandra-3 (relying only on the dependency with the official image makes the status somehow uncertain, and I needed this for testing a different component).

Then just create you keyspaces and tables, or let your component do so.