Make Juno migrations config independent

This patch amends migrations added after the icehouse release and before the healing migration. Migrations are changed in a way that they are not anymore dependent on configuration parameters but are anyway aware of the fact that the database has not yet been healed. To this aim, amended migrations now will need to inspect the current schema and cannot be anymore be used in offline mode; this is consistent with the behaviour of the healing migration. This patch does not remove the logic for generating and managing configuration-dependent migrations. For this reason upgrade and downgrade routines still accept the active_plugins parameter, which will not be used. Change-Id: I9d55a01c64ef555b7774099f497c9eea596aea6e Partially-implements: blueprint reorganize-migrations
2014-07-23 12:16:21 -07:00 · 2014-07-23 12:16:21 -07:00 · 65e498acb3
commit 65e498acb3
parent a141d57d89
13 changed files with 347 additions and 252 deletions
--- a/neutron/db/migration/init.py
+++ b/neutron/db/migration/init.py
@ -14,6 +14,9 @@
 #
 # @author: Mark McClain, DreamHost

+import functools
+
+from alembic import context
 from alembic import op
 import sqlalchemy as sa

@ -22,6 +25,75 @@ OVS_PLUGIN = ('neutron.plugins.openvswitch.ovs_neutron_plugin'
 CISCO_PLUGIN = 'neutron.plugins.cisco.network_plugin.PluginV2'


+def skip_if_offline(func):
+    """Decorator for skipping migrations in offline mode."""
+    @functools.wraps(func)
+    def decorator(*args, **kwargs):
+        if context.is_offline_mode():
+            return
+        return func(*args, **kwargs)
+
+    return decorator
+
+
+def raise_if_offline(func):
+    """Decorator for raising if a function is called in offline mode."""
+    @functools.wraps(func)
+    def decorator(*args, **kwargs):
+        if context.is_offline_mode():
+            raise RuntimeError(_("%s cannot be called while in offline mode") %
+                               func.__name__)
+        return func(*args, **kwargs)
+
+    return decorator
+
+
+@raise_if_offline
+def schema_has_table(table_name):
+    """Check whether the specified table exists in the current schema.
+
+    This method cannot be executed in offline mode.
+    """
+    bind = op.get_bind()
+    insp = sa.engine.reflection.Inspector.from_engine(bind)
+    return table_name in insp.get_table_names()
+
+
+@raise_if_offline
+def schema_has_column(table_name, column_name):
+    """Check whether the specified column exists in the current schema.
+
+    This method cannot be executed in offline mode.
+    """
+    bind = op.get_bind()
+    insp = sa.engine.reflection.Inspector.from_engine(bind)
+    # first check that the table exists
+    if not schema_has_table(table_name):
+        return
+    # check whether column_name exists in table columns
+    return column_name in [column['name'] for column in
+                           insp.get_columns(table_name)]
+
+
+@raise_if_offline
+def alter_column_if_exists(table_name, column_name, **kwargs):
+    """Alter a column only if it exists in the schema."""
+    if schema_has_column(table_name, column_name):
+        op.alter_column(table_name, column_name, **kwargs)
+
+
+@raise_if_offline
+def drop_table_if_exists(table_name):
+    if schema_has_table(table_name):
+        op.drop_table(table_name)
+
+
+@raise_if_offline
+def rename_table_if_exists(old_table_name, new_table_name):
+    if schema_has_table(old_table_name):
+        op.rename_table(old_table_name, new_table_name)
+
+
 def should_run(active_plugins, migrate_plugins):
    if '*' in migrate_plugins:
        return True
--- a/neutron/db/migration/alembic_migrations/versions/10cd28e692e9_nuage_extraroute.py
+++ b/neutron/db/migration/alembic_migrations/versions/10cd28e692e9_nuage_extraroute.py
@ -25,11 +25,6 @@ Create Date: 2014-05-14 14:47:53.148132
 revision = '10cd28e692e9'
 down_revision = '1b837a7125a9'

-# Change to ['*'] if this migration applies to all plugins
-
-migration_for_plugins = [
-    'neutron.plugins.nuage.plugin.NuagePlugin'
-]

 from alembic import op
 import sqlalchemy as sa
@ -38,9 +33,6 @@ from neutron.db import migration


 def upgrade(active_plugins=None, options=None):
-    if not migration.should_run(active_plugins, migration_for_plugins):
-        return
-
    op.create_table(
        'routerroutes_mapping',
        sa.Column('router_id', sa.String(length=36), nullable=False),
@ -48,21 +40,27 @@ def upgrade(active_plugins=None, options=None):
        sa.ForeignKeyConstraint(['router_id'], ['routers.id'],
                                ondelete='CASCADE'),
    )
-    op.create_table(
-        'routerroutes',
-        sa.Column('destination', sa.String(length=64), nullable=False),
-        sa.Column('nexthop', sa.String(length=64), nullable=False),
-        sa.Column('router_id', sa.String(length=36), nullable=False),
-        sa.ForeignKeyConstraint(['router_id'], ['routers.id'],
-                                ondelete='CASCADE'),
-        sa.PrimaryKeyConstraint('destination', 'nexthop',
-                                'router_id'),
-    )
+    # This table might already exist as it might have been created
+    # if another plugin was configured before the nuage one
+    if op.get_bind().engine.dialect.name == 'postgresql':
+        migration.create_table_if_not_exist_psql(
+            'routerroutes',
+            ("(destination VARCHAR(64) NOT NULL,"
+             "nexthop VARCHAR(64) NOT NULL,"
+             "router_id VARCHAR(36) NOT NULL,"
+             "PRIMARY KEY (destination, nexthop, router_id),"
+             "FOREIGN KEY (router_id) REFERENCES routers (id) "
+             "ON DELETE CASCADE ON UPDATE CASCADE)"))
+    else:
+        op.execute("CREATE TABLE IF NOT EXISTS routerroutes( "
+                   "destination VARCHAR(64) NOT NULL,"
+                   "nexthop VARCHAR(64) NOT NULL,"
+                   "router_id VARCHAR(36) NOT NULL,"
+                   "PRIMARY KEY (destination, nexthop, router_id),"
+                   "FOREIGN KEY (router_id) REFERENCES routers (id) "
+                   "ON DELETE CASCADE ON UPDATE CASCADE)")


 def downgrade(active_plugins=None, options=None):
-    if not migration.should_run(active_plugins, migration_for_plugins):
-        return
-
-    op.drop_table('routerroutes')
-    op.drop_table('routerroutes_mapping')
+    # The routerroutes table should not be dropped
+    op.execute('DROP TABLE IF EXISTS routerroutes_mapping')
--- a/neutron/db/migration/alembic_migrations/versions/1b837a7125a9_cisco_apic_driver.py
+++ b/neutron/db/migration/alembic_migrations/versions/1b837a7125a9_cisco_apic_driver.py
@ -25,20 +25,12 @@ Create Date: 2014-02-13 09:35:19.147619
 revision = '1b837a7125a9'
 down_revision = '6be312499f9'

-migration_for_plugins = [
-    'neutron.plugins.ml2.plugin.Ml2Plugin'
-]

 from alembic import op
 import sqlalchemy as sa

-from neutron.db import migration
-

 def upgrade(active_plugins=None, options=None):
-    if not migration.should_run(active_plugins, migration_for_plugins):
-        return
-
    op.create_table(
        'cisco_ml2_apic_epgs',
        sa.Column('network_id', sa.String(length=255), nullable=False),
@ -66,9 +58,6 @@ def upgrade(active_plugins=None, options=None):


 def downgrade(active_plugins=None, options=None):
-    if not migration.should_run(active_plugins, migration_for_plugins):
-        return
-
    op.drop_table('cisco_ml2_apic_contracts')
    op.drop_table('cisco_ml2_apic_port_profiles')
    op.drop_table('cisco_ml2_apic_epgs')
--- a/neutron/db/migration/alembic_migrations/versions/1e5dd1d09b22_set_not_null_fields_lb_stats.py
+++ b/neutron/db/migration/alembic_migrations/versions/1e5dd1d09b22_set_not_null_fields_lb_stats.py
@ -27,40 +27,51 @@ down_revision = '54f7549a0e5f'

 # Change to ['*'] if this migration applies to all plugins

-migration_for_plugins = [
-    'neutron.services.loadbalancer.plugin.LoadBalancerPlugin'
-]
+# This migration will be executed only if the neutron DB schema
+# contains the tables for load balancing service plugin.
+# This migration will be skipped when executed in offline mode.
+

-from alembic import op
 import sqlalchemy as sa

-
 from neutron.db import migration


+@migration.skip_if_offline
 def upgrade(active_plugins=None, options=None):
-    if not migration.should_run(active_plugins, migration_for_plugins):
-        return
-
-    op.alter_column('poolstatisticss', 'bytes_in', nullable=False,
-                    existing_type=sa.BigInteger())
-    op.alter_column('poolstatisticss', 'bytes_out', nullable=False,
-                    existing_type=sa.BigInteger())
-    op.alter_column('poolstatisticss', 'active_connections', nullable=False,
-                    existing_type=sa.BigInteger())
-    op.alter_column('poolstatisticss', 'total_connections', nullable=False,
-                    existing_type=sa.BigInteger())
+    migration.alter_column_if_exists(
+        'poolstatisticss', 'bytes_in',
+        nullable=False,
+        existing_type=sa.BigInteger())
+    migration.alter_column_if_exists(
+        'poolstatisticss', 'bytes_out',
+        nullable=False,
+        existing_type=sa.BigInteger())
+    migration.alter_column_if_exists(
+        'poolstatisticss', 'active_connections',
+        nullable=False,
+        existing_type=sa.BigInteger())
+    migration.alter_column_if_exists(
+        'poolstatisticss', 'total_connections',
+        nullable=False,
+        existing_type=sa.BigInteger())


+@migration.skip_if_offline
 def downgrade(active_plugins=None, options=None):
-    if not migration.should_run(active_plugins, migration_for_plugins):
-        return
-
-    op.alter_column('poolstatisticss', 'bytes_in', nullable=True,
-                    existing_type=sa.BigInteger())
-    op.alter_column('poolstatisticss', 'bytes_out', nullable=True,
-                    existing_type=sa.BigInteger())
-    op.alter_column('poolstatisticss', 'active_connections', nullable=True,
-                    existing_type=sa.BigInteger())
-    op.alter_column('poolstatisticss', 'total_connections', nullable=True,
-                    existing_type=sa.BigInteger())
+    migration.alter_column_if_exists(
+        'poolstatisticss', 'bytes_in',
+        nullable=True,
+        existing_type=sa.BigInteger())
+    migration.alter_column_if_exists(
+        'poolstatisticss', 'bytes_out',
+        nullable=True,
+        existing_type=sa.BigInteger())
+    migration.alter_column_if_exists(
+        'poolstatisticss', 'active_connections',
+        nullable=True,
+        existing_type=sa.BigInteger())
+    migration.alter_column_if_exists(
+        'poolstatisticss', 'total_connections',
+        nullable=True,
+        existing_type=sa.BigInteger())
--- a/neutron/db/migration/alembic_migrations/versions/2db5203cb7a9_nuage_floatingip.py
+++ b/neutron/db/migration/alembic_migrations/versions/2db5203cb7a9_nuage_floatingip.py
@ -25,20 +25,21 @@ Create Date: 2014-05-19 16:39:42.048125
 revision = '2db5203cb7a9'
 down_revision = '10cd28e692e9'

-migration_for_plugins = [
-    'neutron.plugins.nuage.plugin.NuagePlugin'
-]

 from alembic import op
 import sqlalchemy as sa

 from neutron.db import migration

+# This migration will be executed only if the neutron DB schema contains
+# the tables for the nuage plugin.
+# This migration will be skipped when executed in offline mode.

+
+@migration.skip_if_offline
 def upgrade(active_plugins=None, options=None):
-    if not migration.should_run(active_plugins, migration_for_plugins):
-        return
-
+    # These tables will be created even if the nuage plugin is not enabled.
+    # This is fine as they would be created anyway by the healing migration.
    op.create_table(
        'nuage_floatingip_pool_mapping',
        sa.Column('fip_pool_id', sa.String(length=36), nullable=False),
@ -59,25 +60,31 @@ def upgrade(active_plugins=None, options=None):
                                ondelete='CASCADE'),
        sa.PrimaryKeyConstraint('fip_id'),
    )
-    op.rename_table('net_partitions', 'nuage_net_partitions')
-    op.rename_table('net_partition_router_mapping',
-                    'nuage_net_partition_router_mapping')
-    op.rename_table('router_zone_mapping', 'nuage_router_zone_mapping')
-    op.rename_table('subnet_l2dom_mapping', 'nuage_subnet_l2dom_mapping')
-    op.rename_table('port_mapping', 'nuage_port_mapping')
-    op.rename_table('routerroutes_mapping', 'nuage_routerroutes_mapping')
+    migration.rename_table_if_exists('net_partitions',
+                                     'nuage_net_partitions')
+    migration.rename_table_if_exists('net_partition_router_mapping',
+                                     'nuage_net_partition_router_mapping')
+    migration.rename_table_if_exists('router_zone_mapping',
+                                     'nuage_router_zone_mapping')
+    migration.rename_table_if_exists('subnet_l2dom_mapping',
+                                     'nuage_subnet_l2dom_mapping')
+    migration.rename_table_if_exists('port_mapping',
+                                     'nuage_port_mapping')
+    migration.rename_table_if_exists('routerroutes_mapping',
+                                     'nuage_routerroutes_mapping')


+@migration.skip_if_offline
 def downgrade(active_plugins=None, options=None):
-    if not migration.should_run(active_plugins, migration_for_plugins):
-        return
-
-    op.drop_table('nuage_floatingip_mapping')
-    op.drop_table('nuage_floatingip_pool_mapping')
-    op.rename_table('nuage_net_partitions', 'net_partitions')
-    op.rename_table('nuage_net_partition_router_mapping',
-                    'net_partition_router_mapping')
-    op.rename_table('nuage_router_zone_mapping', 'router_zone_mapping')
-    op.rename_table('nuage_subnet_l2dom_mapping', 'subnet_l2dom_mapping')
-    op.rename_table('nuage_port_mapping', 'port_mapping')
-    op.rename_table('nuage_routerroutes_mapping', 'routerroutes_mapping')
+    migration.drop_table_if_exists('nuage_floatingip_mapping')
+    migration.drop_table_if_exists('nuage_floatingip_pool_mapping')
+    migration.rename_table_if_exists('nuage_net_partitions', 'net_partitions')
+    migration.rename_table_if_exists('nuage_net_partition_router_mapping',
+                                     'net_partition_router_mapping')
+    migration.rename_table_if_exists('nuage_router_zone_mapping',
+                                     'router_zone_mapping')
+    migration.rename_table_if_exists('nuage_subnet_l2dom_mapping',
+                                     'subnet_l2dom_mapping')
+    migration.rename_table_if_exists('nuage_port_mapping', 'port_mapping')
+    migration.rename_table_if_exists('nuage_routerroutes_mapping',
+                                     'routerroutes_mapping')
--- a/neutron/db/migration/alembic_migrations/versions/33c3db036fe4_set_length_of_description_field_metering.py
+++ b/neutron/db/migration/alembic_migrations/versions/33c3db036fe4_set_length_of_description_field_metering.py
@ -25,12 +25,6 @@ Create Date: 2014-03-25 11:04:27.341830
 revision = '33c3db036fe4'
 down_revision = 'b65aa907aec'

-# Change to ['*'] if this migration applies to all plugins
-
-migration_for_plugins = [
-    'neutron.services.metering.metering_plugin.MeteringPlugin'
-]
-
 from alembic import op
 import sqlalchemy as sa

@ -38,9 +32,6 @@ from neutron.db import migration


 def upgrade(active_plugins=None, options=None):
-    if not migration.should_run(active_plugins, migration_for_plugins):
-        return
-
    if op.get_bind().engine.dialect.name == 'postgresql':
        migration.create_table_if_not_exist_psql(
            'meteringlabels',
@ -60,7 +51,4 @@ def upgrade(active_plugins=None, options=None):


 def downgrade(active_plugins=None, options=None):
-    if not migration.should_run(active_plugins, migration_for_plugins):
-        return
-
    pass
--- a/neutron/db/migration/alembic_migrations/versions/4eca4a84f08a_remove_ml2_cisco_cred_db.py
+++ b/neutron/db/migration/alembic_migrations/versions/4eca4a84f08a_remove_ml2_cisco_cred_db.py
@ -25,35 +25,31 @@ Create Date: 2014-04-10 19:32:46.697189
 revision = '4eca4a84f08a'
 down_revision = '33c3db036fe4'

-# Change to ['*'] if this migration applies to all plugins
-
-migration_for_plugins = [
-    'neutron.plugins.ml2.plugin.Ml2Plugin'
-]

 from alembic import op
-import sqlalchemy as sa

 from neutron.db import migration


 def upgrade(active_plugins=None, options=None):
-    if not migration.should_run(active_plugins, migration_for_plugins):
-        return
-
-    op.drop_table('cisco_ml2_credentials')
+    op.execute('DROP TABLE IF EXISTS cisco_ml2_credentials')


 def downgrade(active_plugins=None, options=None):
-    if not migration.should_run(active_plugins, migration_for_plugins):
-        return
-
-    op.create_table(
-        'cisco_ml2_credentials',
-        sa.Column('credential_id', sa.String(length=255), nullable=True),
-        sa.Column('tenant_id', sa.String(length=255), nullable=False),
-        sa.Column('credential_name', sa.String(length=255), nullable=False),
-        sa.Column('user_name', sa.String(length=255), nullable=True),
-        sa.Column('password', sa.String(length=255), nullable=True),
-        sa.PrimaryKeyConstraint('tenant_id', 'credential_name')
-    )
+    if op.get_bind().engine.dialect.name == 'postgresql':
+        migration.create_table_if_not_exist_psql(
+            'cisco_ml2_credentials',
+            ("(credential_id VARCHAR(255) NULL,"
+             "tenant_id VARCHAR(255) NOT NULL,"
+             "credential_name VARCHAR(255) NOT NULL,"
+             "user_name VARCHAR(255) NULL,"
+             "password VARCHAR(255) NULL,"
+             "PRIMARY KEY (tenant_id, credential_name))"))
+    else:
+        op.execute('CREATE TABLE IF NOT EXISTS cisco_ml2_credentials( '
+                   'credential_id VARCHAR(255) NULL,'
+                   'tenant_id VARCHAR(255) NOT NULL,'
+                   'credential_name VARCHAR(255) NOT NULL,'
+                   'user_name VARCHAR(255) NULL,'
+                   'password VARCHAR(255) NULL,'
+                   'PRIMARY KEY (tenant_id, credential_name))')
--- a/neutron/db/migration/alembic_migrations/versions/5446f2a45467_set_server_default.py
+++ b/neutron/db/migration/alembic_migrations/versions/5446f2a45467_set_server_default.py
@ -26,33 +26,28 @@ revision = '5446f2a45467'
 down_revision = '2db5203cb7a9'


-from alembic import op
 import sqlalchemy as sa
 import sqlalchemy.sql


+from neutron.db import migration
 from neutron.plugins.cisco.common import cisco_constants

-PLUGINS = {
-    'brocade': 'neutron.plugins.brocade.NeutronPlugin.BrocadePluginV2',
-    'cisco': 'neutron.plugins.cisco.network_plugin.PluginV2',
-    'ml2': 'neutron.plugins.ml2.plugin.Ml2Plugin',
-    'mlnx': 'neutron.plugins.mlnx.mlnx_plugin.MellanoxEswitchPlugin',
-    'vmware': [
-        'neutron.plugins.nicira.NeutronPlugin.NvpPluginV2',
-        'neutron.plugins.nicira.NeutronServicePlugin.NvpAdvancedPlugin',
-        'neutron.plugins.vmware.plugin.NsxPlugin',
-        'neutron.plugins.vmware.plugin.NsxServicePlugin',
-    ],
-    'agents': [
-        'neutron.plugins.linuxbridge.lb_neutron_plugin.LinuxBridgePluginV2',
-        'neutron.plugins.nec.nec_plugin.NECPluginV2',
-        'neutron.plugins.oneconvergence.plugin.OneConvergencePluginV2',
-        'neutron.plugins.openvswitch.ovs_neutron_plugin.OVSNeutronPluginV2',
-        'neutron.plugins.ibm.sdnve_neutron_plugin.SdnvePluginV2',
-        'neutron.services.loadbalancer.plugin.LoadBalancerPlugin',
-    ],
-}
+# This migration will be executed only if then Neutron db contains tables for
+# selected plugins and agents.
+# required tables and columns are:
+# brocade_ports.port_id
+# segmentation_id_llocation.allocated
+# cisco_n1kv_profile_bindings.tenant_id
+# cisco_network_profiles.multicast_ip_index
+# cisco_n1kv_vlan_allocations.allocated
+# nsxrouterextattributess.service_router
+# nsxrouterextattributess.distributed
+# qosqueues.default
+# agents.admin_state_up
+# ml2_gre_allocations.allocated
+# ml2_vxlan_allocations.allocated
+# This migration will be skipped when executed offline mode.


 def upgrade(active_plugins=None, options=None):
@ -63,37 +58,33 @@ def downgrade(active_plugins=None, options=None):
    run(active_plugins, None)


+@migration.skip_if_offline
 def run(active_plugins, default):
-    if PLUGINS['ml2'] in active_plugins:
-        set_default_ml2(default)
-    if PLUGINS['mlnx'] in active_plugins:
-        set_default_agents(default)
-        set_default_mlnx(default)
-    if PLUGINS['brocade'] in active_plugins:
-        set_default_agents(default)
-        set_default_brocade(default)
-    if PLUGINS['cisco'] in active_plugins:
-        set_default_cisco(default)
-    if set(PLUGINS['vmware']) & set(active_plugins):
-            set_default_vmware(default)
-            set_default_agents(default)
-    if set(PLUGINS['agents']) & set(active_plugins):
-        set_default_agents(default)
+    set_default_ml2(default)
+    set_default_mlnx(default)
+    set_default_brocade(default)
+    set_default_cisco(default)
+    set_default_vmware(default)
+    set_default_agents(default)


 def set_default_brocade(default):
    if default:
        default = ''
-    op.alter_column('brocadeports', 'port_id',
-                    server_default=default, existing_type=sa.String(36))
+    migration.alter_column_if_exists(
+        'brocadeports', 'port_id',
+        server_default=default,
+        existing_type=sa.String(36))


 def set_default_mlnx(default):
    if default:
        default = sqlalchemy.sql.false()
-    op.alter_column('segmentation_id_allocation', 'allocated',
-                    server_default=default, existing_nullable=False,
-                    existing_type=sa.Boolean)
+    migration.alter_column_if_exists(
+        'segmentation_id_allocation', 'allocated',
+        server_default=default,
+        existing_nullable=False,
+        existing_type=sa.Boolean)


 def set_default_cisco(default):
@ -102,47 +93,61 @@ def set_default_cisco(default):
    profile_default = '0' if default else None
    if default:
        default = sqlalchemy.sql.false()
-    op.alter_column('cisco_n1kv_profile_bindings', 'tenant_id',
-                    existing_type=sa.String(length=36),
-                    server_default=profile_binding_default,
-                    existing_nullable=False)
-    op.alter_column('cisco_network_profiles', 'multicast_ip_index',
-                    server_default=profile_default, existing_type=sa.Integer)
-    op.alter_column('cisco_n1kv_vlan_allocations', 'allocated',
-                    existing_type=sa.Boolean,
-                    server_default=default, existing_nullable=False)
-    op.alter_column('cisco_n1kv_vxlan_allocations', 'allocated',
-                    existing_type=sa.Boolean,
-                    server_default=default, existing_nullable=False)
+    migration.alter_column_if_exists(
+        'cisco_n1kv_profile_bindings', 'tenant_id',
+        existing_type=sa.String(length=36),
+        server_default=profile_binding_default,
+        existing_nullable=False)
+    migration.alter_column_if_exists(
+        'cisco_network_profiles', 'multicast_ip_index',
+        server_default=profile_default,
+        existing_type=sa.Integer)
+    migration.alter_column_if_exists(
+        'cisco_n1kv_vlan_allocations', 'allocated',
+        existing_type=sa.Boolean,
+        server_default=default,
+        existing_nullable=False)


 def set_default_vmware(default=None):
    if default:
        default = sqlalchemy.sql.false()
-    op.alter_column('nsxrouterextattributess', 'service_router',
-                    server_default=default, existing_nullable=False,
-                    existing_type=sa.Boolean)
-    op.alter_column('nsxrouterextattributess', 'distributed',
-                    server_default=default, existing_nullable=False,
-                    existing_type=sa.Boolean)
-    op.alter_column('qosqueues', 'default',
-                    server_default=default, existing_type=sa.Boolean)
+    migration.alter_column_if_exists(
+        'nsxrouterextattributess', 'service_router',
+        server_default=default,
+        existing_nullable=False,
+        existing_type=sa.Boolean)
+    migration.alter_column_if_exists(
+        'nsxrouterextattributess', 'distributed',
+        server_default=default,
+        existing_nullable=False,
+        existing_type=sa.Boolean)
+    migration.alter_column_if_exists(
+        'qosqueues', 'default',
+        server_default=default,
+        existing_type=sa.Boolean)


 def set_default_agents(default=None):
    if default:
        default = sqlalchemy.sql.true()
-    op.alter_column('agents', 'admin_state_up',
-                    server_default=default, existing_nullable=False,
-                    existing_type=sa.Boolean)
+    migration.alter_column_if_exists(
+        'agents', 'admin_state_up',
+        server_default=default,
+        existing_nullable=False,
+        existing_type=sa.Boolean)


 def set_default_ml2(default=None):
    if default:
        default = sqlalchemy.sql.false()
-    op.alter_column('ml2_gre_allocations', 'allocated',
-                    server_default=default, existing_nullable=False,
-                    existing_type=sa.Boolean)
-    op.alter_column('ml2_vxlan_allocations', 'allocated',
-                    server_default=default, existing_nullable=False,
-                    existing_type=sa.Boolean)
+    migration.alter_column_if_exists(
+        'ml2_gre_allocations', 'allocated',
+        server_default=default,
+        existing_nullable=False,
+        existing_type=sa.Boolean)
+    migration.alter_column_if_exists(
+        'ml2_vxlan_allocations', 'allocated',
+        server_default=default,
+        existing_nullable=False,
+        existing_type=sa.Boolean)
--- a/neutron/db/migration/alembic_migrations/versions/54f7549a0e5f_set_not_null_peer_address.py
+++ b/neutron/db/migration/alembic_migrations/versions/54f7549a0e5f_set_not_null_peer_address.py
@ -25,30 +25,27 @@ Create Date: 2014-03-17 11:00:17.539028
 revision = '54f7549a0e5f'
 down_revision = 'icehouse'

-# Change to ['*'] if this migration applies to all plugins
+# This migration will be executed only if the neutron DB schema
+# contains the tables for VPN service plugin.
+# This migration will be skipped when executed in offline mode.

-migration_for_plugins = [
-    'neutron.services.vpn.plugin.VPNDriverPlugin'
-]

-from alembic import op
 import sqlalchemy as sa

-
 from neutron.db import migration


+@migration.skip_if_offline
 def upgrade(active_plugins=None, options=None):
-    if not migration.should_run(active_plugins, migration_for_plugins):
-        return
-
-    op.alter_column('ipsec_site_connections', 'peer_address',
-                    existing_type=sa.String(255), nullable=False)
+    migration.alter_column_if_exists(
+        'ipsec_site_connections', 'peer_address',
+        existing_type=sa.String(255),
+        nullable=False)


+@migration.skip_if_offline
 def downgrade(active_plugins=None, options=None):
-    if not migration.should_run(active_plugins, migration_for_plugins):
-        return
-
-    op.alter_column('ipsec_site_connections', 'peer_address', nullable=True,
-                    existing_type=sa.String(255))
+    migration.alter_column_if_exists(
+        'ipsec_site_connections', 'peer_address',
+        nullable=True,
+        existing_type=sa.String(255))
--- a/neutron/db/migration/alembic_migrations/versions/6be312499f9_set_not_null_vlan_id_cisco.py
+++ b/neutron/db/migration/alembic_migrations/versions/6be312499f9_set_not_null_vlan_id_cisco.py
@ -25,30 +25,27 @@ Create Date: 2014-03-27 14:38:12.571173
 revision = '6be312499f9'
 down_revision = 'd06e871c0d5'

-# Change to ['*'] if this migration applies to all plugins
+# This migration will be executed only if the neutron DB schema
+# contains the tables for the cisco plugin.
+# This migration will be skipped when executed in offline mode.

-migration_for_plugins = [
-    'neutron.plugins.cisco.network_plugin.PluginV2'
-]
-
-from alembic import op
 import sqlalchemy as sa


 from neutron.db import migration


+@migration.skip_if_offline
 def upgrade(active_plugins=None, options=None):
-    if not migration.should_run(active_plugins, migration_for_plugins):
-        return
-
-    op.alter_column('cisco_nexusport_bindings', 'vlan_id', nullable=False,
-                    existing_type=sa.Integer)
+    migration.alter_column_if_exists(
+        'cisco_nexusport_bindings', 'vlan_id',
+        nullable=False,
+        existing_type=sa.Integer)


+@migration.skip_if_offline
 def downgrade(active_plugins=None, options=None):
-    if not migration.should_run(active_plugins, migration_for_plugins):
-        return
-
-    op.alter_column('cisco_nexusport_bindings', 'vlan_id', nullable=True,
-                    existing_type=sa.Integer)
+    migration.alter_column_if_exists(
+        'cisco_nexusport_bindings', 'vlan_id',
+        nullable=True,
+        existing_type=sa.Integer)
--- a/neutron/db/migration/alembic_migrations/versions/b65aa907aec_set_length_of_protocol_field.py
+++ b/neutron/db/migration/alembic_migrations/versions/b65aa907aec_set_length_of_protocol_field.py
@ -16,7 +16,7 @@
 """set_length_of_protocol_field

 Revision ID: b65aa907aec
-Revises: 2447ad0e9585
+Revises: 1e5dd1d09b22
 Create Date: 2014-03-21 16:30:10.626649

 """
@ -25,28 +25,22 @@ Create Date: 2014-03-21 16:30:10.626649
 revision = 'b65aa907aec'
 down_revision = '1e5dd1d09b22'

-# Change to ['*'] if this migration applies to all plugins
+# This migration will be executed only if then Neutron db contains tables for
+# the firewall service plugin
+# This migration will not be executed in offline mode

-migration_for_plugins = [
-    'neutron.services.firewall.fwaas_plugin.FirewallPlugin'
-]
-
-from alembic import op
 import sqlalchemy as sa

 from neutron.db import migration


+@migration.skip_if_offline
 def upgrade(active_plugins=None, options=None):
-    if not migration.should_run(active_plugins, migration_for_plugins):
-        return
-
-    op.alter_column('firewall_rules', 'protocol', type_=sa.String(40),
-                    existing_nullable=True)
+    migration.alter_column_if_exists(
+        'firewall_rules', 'protocol',
+        type_=sa.String(40),
+        existing_nullable=True)


 def downgrade(active_plugins=None, options=None):
-    if not migration.should_run(active_plugins, migration_for_plugins):
-        return
-
    pass
--- a/neutron/db/migration/alembic_migrations/versions/d06e871c0d5_set_admin_state_up_not_null_ml2.py
+++ b/neutron/db/migration/alembic_migrations/versions/d06e871c0d5_set_admin_state_up_not_null_ml2.py
@ -25,30 +25,28 @@ Create Date: 2014-03-21 17:22:20.545186
 revision = 'd06e871c0d5'
 down_revision = '4eca4a84f08a'

-# Change to ['*'] if this migration applies to all plugins
+# This migration will be executed only if the neutron DB schema
+# contains the tables for the ML2 plugin brocade driver.
+# This migration will be skipped when executed in offline mode.

-migration_for_plugins = [
-    'neutron.plugins.ml2.plugin.Ml2Plugin'
-]

-from alembic import op
 import sqlalchemy as sa


 from neutron.db import migration


+@migration.skip_if_offline
 def upgrade(active_plugins=None, options=None):
-    if not migration.should_run(active_plugins, migration_for_plugins):
-        return
-
-    op.alter_column('ml2_brocadeports', 'admin_state_up', nullable=False,
-                    existing_type=sa.Boolean)
+    migration.alter_column_if_exists(
+        'ml2_brocadeports', 'admin_state_up',
+        nullable=False,
+        existing_type=sa.Boolean)


+@migration.skip_if_offline
 def downgrade(active_plugins=None, options=None):
-    if not migration.should_run(active_plugins, migration_for_plugins):
-        return
-
-    op.alter_column('ml2_brocadeports', 'admin_state_up', nullable=True,
-                    existing_type=sa.Boolean)
+    migration.alter_column_if_exists(
+        'ml2_brocadeports', 'admin_state_up',
+        nullable=True,
+        existing_type=sa.Boolean)
--- a/neutron/tests/unit/test_db_migration.py
+++ b/neutron/tests/unit/test_db_migration.py
@ -25,6 +25,16 @@ from neutron.tests import base


 class TestDbMigration(base.BaseTestCase):
+
+    def setUp(self):
+        super(TestDbMigration, self).setUp()
+        mock.patch('alembic.op.get_bind').start()
+        self.mock_alembic_is_offline = mock.patch(
+            'alembic.context.is_offline_mode', return_value=False).start()
+        self.mock_alembic_is_offline.return_value = False
+        self.mock_sa_inspector = mock.patch(
+            'sqlalchemy.engine.reflection.Inspector').start()
+
    def test_should_run_plugin_in_list(self):
        self.assertTrue(migration.should_run(['foo'], ['foo', 'bar']))
        self.assertFalse(migration.should_run(['foo'], ['bar']))
@ -32,6 +42,39 @@ class TestDbMigration(base.BaseTestCase):
    def test_should_run_plugin_wildcard(self):
        self.assertTrue(migration.should_run(['foo'], ['*']))

+    def _prepare_mocked_sqlalchemy_inspector(self):
+        mock_inspector = mock.MagicMock()
+        mock_inspector.get_table_names.return_value = ['foo', 'bar']
+        mock_inspector.get_columns.return_value = [{'name': 'foo_column'},
+                                                   {'name': 'bar_column'}]
+        self.mock_sa_inspector.from_engine.return_value = mock_inspector
+
+    def test_schema_has_table(self):
+        self._prepare_mocked_sqlalchemy_inspector()
+        self.assertTrue(migration.schema_has_table('foo'))
+
+    def test_schema_has_table_raises_if_offline(self):
+        self.mock_alembic_is_offline.return_value = True
+        self.assertRaises(RuntimeError, migration.schema_has_table, 'foo')
+
+    def test_schema_has_column_missing_table(self):
+        self._prepare_mocked_sqlalchemy_inspector()
+        self.assertFalse(migration.schema_has_column('meh', 'meh'))
+
+    def test_schema_has_column(self):
+        self._prepare_mocked_sqlalchemy_inspector()
+        self.assertTrue(migration.schema_has_column('foo', 'foo_column'))
+
+    def test_schema_has_column_raises_if_offline(self):
+        self.mock_alembic_is_offline.return_value = True
+        self.assertRaises(RuntimeError, migration.schema_has_column,
+                          'foo', 'foo_col')
+
+    def test_schema_has_column_missing_column(self):
+        self._prepare_mocked_sqlalchemy_inspector()
+        self.assertFalse(migration.schema_has_column(
+            'foo', column_name='meh'))
+

 class TestCli(base.BaseTestCase):
    def setUp(self):