postgres with ssl cerficiates workaround for initdb and non empty data dir

docker-compose.yml

# generate certificate and key with openssl and then mount them
version: '2.3'
  postgres:
    image: postgres:alpine
    # specify location to the keys explicitly
    command: -c ssl=on -c ssl_cert_file=/var/lib/postgresql/server.crt -c ssl_key_file=/var/lib/postgresql/server.key
    environment:
      POSTGRES_DB: mydb
      POSTGRES_USER: user
      POSTGRES_PASSWORD: secret
    # mount outside of the data dir so you don't get errors about the data dir not being empty
    volumes:
      - ./ca/server.crt:/var/lib/postgresql/server.crt
      - ./ca/server.key:/var/lib/postgresql/server.key