By default, data in OpenStack instances is stored on ‘ephemeral’ disks. These disks remain with the instance throughout its lifetime. When you terminate the instance, that storage and all the data stored on it disappears. Ephemeral storage is allocated to a single instance and cannot be moved to another instance.
This section introduces block storage, also known as volume storage, which provides access to persistent storage devices. You interact with block storage by attaching volumes to running instances just as you might attach a USB drive to a physical server. You can detach volumes from one instance and reattach them to another instance and the data remains intact. The OpenStack Block Storage (cinder) project implements block storage.
Though you might have configured Object Storage to store images, the Fractal application needs a database to track the location of, and parameters that were used to create, images in Object Storage. This database server cannot fail.
If you are an advanced user, think about how you might remove the database from the architecture and replace it with Object Storage metadata, and then contribute these steps to Going crazy.
Otherwise, continue reading to learn how to work with, and move the Fractal application database server to use, block storage.
Later on, you will use a Block Storage volume to provide persistent storage for the database server for the Fractal application. But first, learn how to create and attach a Block Storage device.
Connect to the API endpoint:
import shade conn = shade.openstack_cloud(cloud='myfavoriteopenstack')
To try it out, make a 1GB volume called ‘test’.
volume = conn.create_volume(size=1, display_name='test')
size is in gigabytes.
To see if the volume creation was successful, list all volumes:
volumes = conn.list_volumes() for vol in volumes: print(vol)
You need a server for the dedicated database. Use the image, flavor, and
keypair that you used in Getting started to launch an
You also need a security group to permit access to the database server (for MySQL, port 3306) from the network:
db_group = conn.create_security_group('database', 'for database service') conn.create_security_group_rule(db_group['name'], 22, 22, 'TCP') conn.create_security_group_rule(db_group['name'], 3306, 3306, 'TCP') userdata = '''#!/usr/bin/env bash curl -L -s http://git.openstack.org/cgit/openstack/faafo/plain/contrib/install.sh | bash -s -- \ -i database -i messaging ''' instance = conn.create_server(wait=True, auto_ip=False, name='app-database', image=image_id, flavor=flavor_id, key_name='demokey', security_groups=[db_group['name']], userdata=userdata)
Create a volume object by using the unique identifier (UUID) for the
volume. Then, use the server object from the previous code snippet to
attach the volume to it at
conn.attach_volume(instance, volume, '/dev/vdb')
Log in to the server to run the following steps.
IP_DATABASE with the IP address of the
database instance and USERNAME to the appropriate user name.
Now prepare the empty block device.
$ ssh -i ~/.ssh/id_rsa USERNAME@IP_DATABASE # fdisk -l Disk /dev/vdb: 1073 MB, 1073741824 bytes 16 heads, 63 sectors/track, 2080 cylinders, total 2097152 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x00000000 Disk /dev/vdb doesn't contain a valid partition table # mke2fs /dev/vdb mke2fs 1.42.9 (4-Feb-2014) Filesystem label= OS type: Linux Block size=4096 (log=2) Fragment size=4096 (log=2) Stride=0 blocks, Stripe width=0 blocks 65536 inodes, 262144 blocks 13107 blocks (5.00%) reserved for the super user First data block=0 Maximum filesystem blocks=268435456 8 block groups 32768 blocks per group, 32768 fragments per group 8192 inodes per group Superblock backups stored on blocks: 32768, 98304, 163840, 229376 Allocating group tables: done Writing inode tables: done Writing superblocks and filesystem accounting information: done # mkdir /mnt/database # mount /dev/vdb /mnt/database
Stop the running MySQL database service and move the database files from
/var/lib/mysql to the new volume, which is temporarily mounted at
# systemctl stop mariadb # mv /var/lib/mysql/* /mnt/database
Sync the file systems and mount the block device that contains the database
# sync # umount /mnt/database # rm -rf /mnt/database # echo "/dev/vdb /var/lib/mysql ext4 defaults 1 2" >> /etc/fstab # mount /var/lib/mysql
Finally, start the stopped MySQL database service and validate that everything works as expected.
# systemctl start mariadb # mysql -ufaafo -ppassword -h localhost faafo -e 'show tables;'
You can detach the volume and reattach it elsewhere, or use the following steps to delete the volume.
The following operations are destructive and result in data loss.
To detach and delete a volume:
conn.detach_volume(instance, volume) conn.delete_volume(volume['id'])
Previously, you manually created the database, which is useful for a single
database that you rarely update. However, the OpenStack
component provides Database as a Service (DBaaS).
This OpenStack Database service is not installed in many clouds right now, but if your cloud supports it, it can make your life a lot easier when working with databases.
SDKs do not generally support the service yet, but you can use the ‘trove’ command-line client to work with it instead.
To install the ‘trove’ command-line client, see Install the OpenStack command-line clients.
To set up environment variables for your cloud in an
Set environment variables using the OpenStack RC file.
Ensure you have an
openrc.sh file, source it, and validate that
your trove client works:
$ cat openrc.sh export OS_USERNAME=your_auth_username export OS_PASSWORD=your_auth_password export OS_TENANT_NAME=your_project_name export OS_AUTH_URL=http://controller:5000/v2.0 export OS_REGION_NAME=your_region_name $ source openrc.sh $ trove --version 1.0.9
For information about supported features and how to work with an existing database service installation, see Database as a Service in OpenStack.
You should now be fairly confident working with Block Storage volumes. For information about other calls, see the volume documentation for your SDK. Or, try one of these tutorial steps: