db: Add initial alembic configuration

No migrations yet: this is simply the output of 'alembic init' with some
minor tweaks.

A note about ordering of requirements is removed from requirements.txt:
it is no longer true with the new dependency resolver introduced in pip
20.3.

Signed-off-by: Stephen Finucane <stephenfin@redhat.com>
Change-Id: I7790222ab5eaf6c47dd386fe472275a3037a9898

6 files changed, 191 insertions, 4 deletions

diff --git a/doc/source/conf.py b/doc/source/conf.py
index 913262c95..0cf74e0e1 100644
--- a/doc/source/conf.py
+++ b/doc/source/conf.py
@@ -178,6 +178,7 @@ apidoc_separate_modules = True
 apidoc_excluded_paths = [
     'cmd',
     'cloudinit',
+    'db/sqlalchemy/migrations/versions',
     'db/sqlalchemy/migrate_repo/versions',
     'engine/resources/aws',
     'engine/resources/openstack',
diff --git a/heat/db/sqlalchemy/alembic.ini b/heat/db/sqlalchemy/alembic.ini
new file mode 100644
index 000000000..b4a2f235a
--- /dev/null
+++ b/heat/db/sqlalchemy/alembic.ini
@@ -0,0 +1,72 @@
+[alembic]
+# path to migration scripts
+script_location = %(here)s/migrations
+
+# sys.path path, will be prepended to sys.path if present.
+# defaults to the current working directory.
+prepend_sys_path = .
+
+# version location specification; This defaults
+# to heat/db/sqlalchemy/migrations/versions.  When using multiple version
+# directories, initial revisions must be specified with --version-path.
+# The path separator used here should be the separator specified by "version_path_separator" below.
+# version_locations = %(here)s/bar:%(here)s/bat:heat/db/sqlalchemy/migrations/versions
+
+# version path separator; As mentioned above, this is the character used to split
+# version_locations. The default within new alembic.ini files is "os", which uses os.pathsep.
+# If this key is omitted entirely, it falls back to the legacy behavior of splitting on spaces and/or commas.
+# Valid values for version_path_separator are:
+#
+# version_path_separator = :
+# version_path_separator = ;
+# version_path_separator = space
+version_path_separator = os  # Use os.pathsep. Default configuration used for new projects.
+
+sqlalchemy.url = sqlite:///heat.db
+
+
+[post_write_hooks]
+# post_write_hooks defines scripts or Python functions that are run
+# on newly generated revision scripts.  See the documentation for further
+# detail and examples
+
+# format using "black" - use the console_scripts runner, against the "black" entrypoint
+# hooks = black
+# black.type = console_scripts
+# black.entrypoint = black
+# black.options = -l 79 REVISION_SCRIPT_FILENAME
+
+# Logging configuration
+[loggers]
+keys = root,sqlalchemy,alembic
+
+[handlers]
+keys = console
+
+[formatters]
+keys = generic
+
+[logger_root]
+level = WARN
+handlers = console
+qualname =
+
+[logger_sqlalchemy]
+level = WARN
+handlers =
+qualname = sqlalchemy.engine
+
+[logger_alembic]
+level = INFO
+handlers =
+qualname = alembic
+
+[handler_console]
+class = StreamHandler
+args = (sys.stderr,)
+level = NOTSET
+formatter = generic
+
+[formatter_generic]
+format = %(levelname)-5.5s [%(name)s] %(message)s
+datefmt = %H:%M:%S
diff --git a/heat/db/sqlalchemy/migrations/README.rst b/heat/db/sqlalchemy/migrations/README.rst
new file mode 100644
index 000000000..b2283fc82
--- /dev/null
+++ b/heat/db/sqlalchemy/migrations/README.rst
@@ -0,0 +1,15 @@
+Database migrations
+===================
+
+This directory contains migrations for the database. These are implemented
+using `alembic`__, a lightweight database migration tool designed for usage
+with `SQLAlchemy`__.
+
+The best place to start understanding Alembic is with its own `tutorial`__. You
+can also play around with the :command:`alembic` command::
+
+    $ alembic --help
+
+.. __: https://alembic.sqlalchemy.org/en/latest/
+.. __: https://www.sqlalchemy.org/
+.. __: https://alembic.sqlalchemy.org/en/latest/tutorial.html
diff --git a/heat/db/sqlalchemy/migrations/env.py b/heat/db/sqlalchemy/migrations/env.py
new file mode 100644
index 000000000..b0df5e9b3
--- /dev/null
+++ b/heat/db/sqlalchemy/migrations/env.py
@@ -0,0 +1,82 @@
+# Licensed under the Apache License, Version 2.0 (the "License"); you may
+# not use this file except in compliance with the License. You may obtain
+# a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+# License for the specific language governing permissions and limitations
+# under the License.
+
+from logging.config import fileConfig
+
+from sqlalchemy import engine_from_config
+from sqlalchemy import pool
+
+from alembic import context
+
+# this is the Alembic Config object, which provides
+# access to the values within the .ini file in use.
+config = context.config
+
+# Interpret the config file for Python logging.
+# This line sets up loggers basically.
+if config.config_file_name is not None:
+    fileConfig(config.config_file_name)
+
+# add your model's MetaData object here
+# for 'autogenerate' support
+# from myapp import mymodel
+# target_metadata = mymodel.Base.metadata
+target_metadata = None
+
+
+def run_migrations_offline() -> None:
+    """Run migrations in 'offline' mode.
+
+    This configures the context with just a URL and not an Engine, though an
+    Engine is acceptable here as well.  By skipping the Engine creation we
+    don't even need a DBAPI to be available.
+
+    Calls to context.execute() here emit the given string to the
+    script output.
+    """
+    url = config.get_main_option("sqlalchemy.url")
+    context.configure(
+        url=url,
+        target_metadata=target_metadata,
+        literal_binds=True,
+        dialect_opts={"paramstyle": "named"},
+    )
+
+    with context.begin_transaction():
+        context.run_migrations()
+
+
+def run_migrations_online() -> None:
+    """Run migrations in 'online' mode.
+
+    In this scenario we need to create an Engine and associate a connection
+    with the context.
+    """
+    connectable = engine_from_config(
+        config.get_section(config.config_ini_section, {}),
+        prefix="sqlalchemy.",
+        poolclass=pool.NullPool,
+    )
+
+    with connectable.connect() as connection:
+        context.configure(
+            connection=connection, target_metadata=target_metadata
+        )
+
+        with context.begin_transaction():
+            context.run_migrations()
+
+
+if context.is_offline_mode():
+    run_migrations_offline()
+else:
+    run_migrations_online()
diff --git a/heat/db/sqlalchemy/migrations/script.py.mako b/heat/db/sqlalchemy/migrations/script.py.mako
new file mode 100644
index 000000000..120937fbc
--- /dev/null
+++ b/heat/db/sqlalchemy/migrations/script.py.mako
@@ -0,0 +1,20 @@
+"""${message}
+
+Revision ID: ${up_revision}
+Revises: ${down_revision | comma,n}
+Create Date: ${create_date}
+"""
+
+from alembic import op
+import sqlalchemy as sa
+${imports if imports else ""}
+
+# revision identifiers, used by Alembic.
+revision = ${repr(up_revision)}
+down_revision = ${repr(down_revision)}
+branch_labels = ${repr(branch_labels)}
+depends_on = ${repr(depends_on)}
+
+
+def upgrade() -> None:
+    ${upgrades if upgrades else "pass"}
diff --git a/requirements.txt b/requirements.txt
index 18150cfc4..7794a608b 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -2,11 +2,8 @@
 # date but we do not test them so no guarantee of having them all correct. If
 # you find any incorrect lower bounds, let us know or propose a fix.
 
-# The order of packages is significant, because pip processes them in the order
-# of appearance. Changing the order has an impact on the overall integration
-# process, which may cause wedges in the gate later.
-
 pbr>=3.1.1 # Apache-2.0
+alembic>=1.8.0 # MIT
 Babel!=2.4.0,>=2.3.4 # BSD
 ddt>=1.4.1 # MIT
 croniter>=0.3.4 # MIT License