add: cross-compile support

The main goal is to be able to build ARM
images on standard x86 hardware. Add simple
functions supported by python-py and
podman-py to enable creation of container
images on emulated architectures.

Change-Id: I1526b460f6e271c2ec63ab3a3b1dc348d742e96d

doc/source/admin/image-building.rst

@@ -526,6 +526,28 @@ variables that will be picked up from the user env:
 Also these variables could be overwritten using ``--build-args``, which have
 precedence.
 
+Cross-compiling
+---------------
+
+It is possible to cross-compile container images in order to, e.g., build
+``aarch64`` images on a ``x86_64`` machine.
+
+To build ``ARM`` images on ``x86_64`` platform, pass the ``--base-arch`` and
+``--platform`` arguments:
+
+.. code-block:: console
+
+   kolla-build --platform linux/arm64 --base-arch aarch64
+
+.. note::
+
+   To make this work on x86_64 platform you can use tools like: `qemu-user-static
+   <https://github.com/multiarch/qemu-user-static>`_ or `binfmt
+   <https://github.com/tonistiigi/binfmt>`_.
+
+   To make this work on Apple Silicon you can use Docker Desktop or Podman
+   Desktop to build ``x86_64`` or native ``ARM`` images.
+
 Known issues
 ============
 

kolla/common/config.py

@@ -138,6 +138,10 @@ _PROFILE_OPTS = [
 
 hostarch = os.uname()[4]
 
+# NOTE: Apple Silicon reports as arm64 which is aarch64
+if hostarch == "arm64":
+    hostarch = "aarch64"
+
 _CLI_OPTS = [
     cfg.StrOpt('base', short='b', default='rocky',
                choices=BASE_OS_DISTRO,
@@ -174,6 +178,10 @@ _CLI_OPTS = [
                help='The network mode for Docker build. Example: host'),
     cfg.BoolOpt('cache', default=True,
                 help='Use the container engine cache when building'),
+    cfg.StrOpt('platform', default=None,
+               help=('The platform to use for a cross-compile build. Should '
+                     'be set in conjunction with "--base-arch" argument. '
+                     'Example: "--platform linux/arm64 --base-arch aarch64"')),
     cfg.MultiOpt('profile', types.String(), short='p',
                  help=('Build a pre-defined set of images, see [profiles]'
                        ' section in config. The default profiles are:'

kolla/image/tasks.py

@@ -400,6 +400,7 @@ class BuildTask(EngineTask):
                     network_mode=self.conf.network_mode,
                     pull=pull,
                     forcerm=self.forcerm,
+                    platform=self.conf.platform,
                     buildargs=buildargs,
                     **kwargs)[1]:
                 if self.conf.engine == engine.Engine.PODMAN.value:

kolla/tests/test_build.py

@@ -168,7 +168,7 @@ class TasksTest(base.TestCase):
         mock_client().images.build.assert_called_once_with(
             path=self.image.path, tag=self.image.canonical_name,
             network_mode='host', nocache=False, rm=True, pull=True,
-            forcerm=True, buildargs=None, **self.build_kwargs)
+            forcerm=True, platform=None, buildargs=None, **self.build_kwargs)
 
         self.assertTrue(builder.success)
 
@@ -185,7 +185,7 @@ class TasksTest(base.TestCase):
         mock_client().images.build.assert_called_once_with(
             path=self.image.path, tag=self.image.canonical_name,
             network_mode='bridge', nocache=False, rm=True, pull=True,
-            forcerm=True, buildargs=None, **self.build_kwargs)
+            forcerm=True, platform=None, buildargs=None, **self.build_kwargs)
 
         self.assertTrue(builder.success)
 
@@ -205,7 +205,8 @@ class TasksTest(base.TestCase):
         mock_client().images.build.assert_called_once_with(
             path=self.image.path, tag=self.image.canonical_name,
             network_mode='host', nocache=False, rm=True, pull=True,
-            forcerm=True, buildargs=build_args, **self.build_kwargs)
+            forcerm=True, platform=None, buildargs=build_args,
+            **self.build_kwargs)
 
         self.assertTrue(builder.success)
 
@@ -224,7 +225,8 @@ class TasksTest(base.TestCase):
         mock_client().images.build.assert_called_once_with(
             path=self.image.path, tag=self.image.canonical_name,
             network_mode='host', nocache=False, rm=True, pull=True,
-            forcerm=True, buildargs=build_args, **self.build_kwargs)
+            forcerm=True, platform=None, buildargs=build_args,
+            **self.build_kwargs)
 
         self.assertTrue(builder.success)
 
@@ -245,7 +247,8 @@ class TasksTest(base.TestCase):
         mock_client().images.build.assert_called_once_with(
             path=self.image.path, tag=self.image.canonical_name,
             network_mode='host', nocache=False, rm=True, pull=True,
-            forcerm=True, buildargs=build_args, **self.build_kwargs)
+            forcerm=True, platform=None, buildargs=build_args,
+            **self.build_kwargs)
 
         self.assertTrue(builder.success)
 

releasenotes/notes/support-image-cross-compile-3b1dc348d742e96d.yaml

@@ -0,0 +1,5 @@
+---
+features:
+  - |
+    Add support for cross-compile. Enable creation of container images
+    on emulated architectures.