Docker has an opportunity to set an environment variable with a dot:
-e "bootstrap.memory_lock=true"
or docker-compose:

#!yaml

    environment:
      - cluster.name=docker-cluster
      - bootstrap.memory_lock=true

And it's requirements for some projects (https://www.elastic.co/guide/en/elasticsearch/reference/current/docker.html)

But bitbucket-pipelines.yml provides only one way for environment variables - as dict. So and we can't use dots in names as in the example above.