Building Guest Images for OpenStack Trove

Overview

When Trove receives a command to create a database instance, it does so by launching a Nova instance based on the appropriate guest image that is stored in Glance. This document shows you the steps to build the guest images.

Note

For testing purpose, the Trove guest images of some specific databases are periodically built and published in http://tarballs.openstack.org/trove/images/ in Trove upstream CI.

High Level Overview of a Trove Guest Instance

At the most basic level, a Trove Guest Instance is a Nova instance launched by Trove in response to a create command. For most of this document, we will confine ourselves to single instance databases; in other words, without the additional complexity of replication or mirroring. Guest instances and Guest images for replicated and mirrored database instances will be addressed specifically in later sections of this document.

This section describes the various components of a Trove Guest Instance.

Operating System and Database

A Trove Guest Instance contains at least a functioning Operating System and the database software that the instance wishes to provide (as a Service). For example, if your chosen operating system is Ubuntu and you wish to deliver MySQL version 5.7, then your guest instance is a Nova instance running the Ubuntu operating system and will have MySQL version 5.7 installed on it.

Trove Guest Agent

Trove supports multiple databases, some of them are relational (RDBMS) and some are non-relational (NoSQL). In order to provide a common management interface to all of these, the Trove Guest Instance has on it a ‘Guest Agent’. The Trove Guest Agent is a component of the Trove system that is specific to the database running on that Guest Instance.

The purpose of the Trove Guest Agent is to implement the Trove Guest Agent API for the specific database. This includes such things as the implementation of the database ‘start’ and ‘stop’ commands. The Trove Guest Agent API is the common API used by Trove to communicate with any guest database, and the Guest Agent is the implementation of that API for the specific database.

The Trove Guest Agent runs inside the Trove Guest Instance.

Injected Configuration for the Guest Agent

When TaskManager launches the guest VM it injects config files into the VM, including:

  • /etc/trove/conf.d/guest_info.conf: Contains some information about the guest, e.g. the guest identifier, the tenant ID, etc.

  • /etc/trove/conf.d/trove-guestagent.conf: The config file for the guest agent service.

Persistent Storage, Networking

The database stores data on persistent storage on Cinder (if CONF.volume_support=True) or ephemeral storage on the Nova instance. The database service is accessible over the tenant network provided when creating the database instance.

The cloud administrator is able to config management networks(CONF.management_networks) that is invisible to the cloud tenants, but used for communication between database instance and the control plane services(e.g. the message queue).

Building Guest Images

Build images using trovestack

trovestack is the recommended tooling provided by Trove community to build the guest images. Before running trovestack command, go to the scripts folder:

git clone https://opendev.org/openstack/trove
cd trove/integration/scripts

The trove guest agent image could be created by running the following command:

$ ./trovestack build-image \
    ${datastore_type} \
    ${guest_os} \
    ${guest_os_release} \
    ${dev_mode} \
    ${guest_username} \
    ${imagepath}
  • Currently, only guest_os=ubuntu and guest_os_release=xenial are fully tested and supported.

  • Default input values:

    datastore_type=mysql
    guest_os=ubuntu
    guest_os_release=xenial
    dev_mode=true
    guest_username=ubuntu
    imagepath=$HOME/images/trove-${guest_os}-${guest_os_release}-${datastore_type}
    
  • dev_mode=true is mainly for testing purpose for trove developers and it’s necessary to build the image on the trove controller host, because the host and the guest VM need to ssh into each other without password. In this mode, when the trove guest agent code is changed, the image doesn’t need to be rebuilt which is convenient for debugging. Trove guest agent will ssh into the controller node and download trove code during the service initialization.

  • if dev_mode=false, the trove code for guest agent is injected into the image at the building time. Now dev_mode=false is still in experimental and not considered production ready yet.

  • Some other global variables:

    • HOST_SCP_USERNAME: Only used in dev mode, this is the user name used by guest agent to connect to the controller host, e.g. in devstack environment, it should be the stack user.

    • GUEST_WORKING_DIR: The place to save the guest image, default value is $HOME/images.

    • TROVE_BRANCH: Only used in dev mode. The branch name of Trove code repository, by default it’s master, use other branches as needed such as stable/train.

For example, in order to build a MySQL image for Ubuntu Xenial operating system in development mode:

$ ./trovestack build-image mysql ubuntu xenial true

Once the image build is finished, the cloud administrator needs to register the image in Glance and register a new datastore or version in Trove using trove-manage command, e.g. after building an image for MySQL 5.7.1:

$ openstack image create ubuntu-mysql-5.7.1-dev \
  --public \
  --disk-format qcow2 \
  --container-format bare \
  --file ~/images/ubuntu-xenial-mysql.qcow2
$ trove-manage datastore_version_update mysql 5.7.1 mysql $image_id "" 1

If you see anything error or need help for the image creation, please ask help either in #openstack-trove IRC channel or sending emails to openstack-discuss@lists.openstack.org mailing list.