Added support for override command directive when conductor is building image

container/core.py

@@ -731,6 +731,13 @@ def conductorcmd_build(engine_name, project_name, services, cache=True, local_py
                     environment=dict(ANSIBLE_CONTAINER=1)
                 )
 
+                if service.get('build_overrides'):
+                    for key in service['build_overrides']:
+                        if key in ['user', 'working_dir', 'command', 'privileged']:
+                            run_kwargs[key] = service['build_overrides'][key]
+
+                    run_kwargs['environment'].update(service['build_overrides']['environment'])
+
                 if service.get('volumes'):
                     for volume in service['volumes']:
                         pieces = volume.split(':')

docs/rst/container_yml/reference.rst

@@ -220,6 +220,8 @@ with a checkmark in the *Supported* column can be used.
 Directive             Definition                                               Supported?
 ===================== ======================================================== ============
 build                 Run Dockerfile based build
+:ref:`build_over`     Service level directives that apply only in container
+                      build time                                               |checkmark|
 cap_add               Add container capabilities
 cap_drop              Drop container capabilities
 command               Command executed by the container at startup             |checkmark|
@@ -290,6 +292,39 @@ Implementation
 
 The following provides details about how specific directives are implemented.
 
+.. _build_over:
+
+build_overrides
+.............
+
+Use for directives that should only be applied during the execution of the ``build`` command. For example,
+consider the following ``container.yml`` file:
+
+.. code-block:: yaml
+
+    version: '2'
+    services:
+      web:
+        from: centos:7
+        command: [nginx]
+        entrypoint: [/usr/bin/entrypoint.sh]
+        ports:
+          - 8000:8000
+        build_overrides:
+          command: /usr/sbin/init
+          user: root
+          working_dir: /somepath
+          environment:
+            - container: docker
+
+
+In this example, when ``ansible-container build`` is executed, the options found in *build_overrides* will
+take effect, and the building container will run command ``/usr/sbin/init`` rather than default ``sh -c "while true; do sleep 1; done``, have extra environment variables ``container=docker`` mapped to the container's environment and the container's working directory will be ``/somepath``.
+
+The ``run`` and ``deploy`` commands ignore *build_overrides*. When ``run`` or ``deploy`` executes, the container will not run the command or use environment variables specified in ``build_overrides`` directive.
+
+Supported directives in ``build_overrides`` are ``command``, ``user``, ``working_dir``, ``privileged`` and ``environment``
+
 .. _depends_on:
 
 depends_on