Merge "Database and User Functions for Cassandra"
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specs/liberty/cassandra-database-user-functions.rst
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specs/liberty/cassandra-database-user-functions.rst
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..
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This work is licensed under a Creative Commons Attribution 3.0 Unported
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License.
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http://creativecommons.org/licenses/by/3.0/legalcode
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Sections of this template were taken directly from the Nova spec
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template at:
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https://github.com/openstack/nova-specs/blob/master/specs/template.rst
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=====================================
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Cassandra Database and User Functions
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=====================================
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Launchpad blueprint:
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https://blueprints.launchpad.net/trove/+spec/cassandra-database-user-functions
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Problem Description
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===================
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The Cassandra datastore currently does not support keyspace [*]_ and
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user management features.
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.. [*] A keyspace is the outermost container for data in Cassandra,
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corresponding closely to a relational database.
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Proposed Change
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===============
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The patch set will implement the following keyspace and user related
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functionality for Cassandra 2.1 datastore:
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User Functions:
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- create/delete/get user
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- list users
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- change password
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- grant/revoke/list access
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- update attributes
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Keyspace Functions:
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- create/delete database
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- list databases
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Configuration
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-------------
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Cassandra stores its configuration in 'cassandra.yaml' file
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(commonly in '/etc/cassandra').
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The node (datastore service) has to be restarted for any changes to the
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configuration file to take effect.
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The configuration template will have to be updated to enable authentication and
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authorization in order to support datastore users and related functions.
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Client-specific settings (authentication defaults) are stored in
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'~/.cassandra/cqlshrc' where '~' is the home directory of the Trove user.
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Database
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--------
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None
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Public API
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----------
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None
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Public API Security
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-------------------
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The current implementation allows original anonymous connections therefore
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making the datastore wide open for anybody with connection URL.
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This has to be changed first as the user functions are not even enabled in this
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setting.
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In Cassandra only SUPERUSERS can create other users and
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grant permissions to database resources.
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Trove uses the 'cassandra' superuser to perform its administrative
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tasks.
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The users it creates are all 'normal' (NOSUPERUSER) accounts.
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The permissions it can grant are also limited to non-superuser
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operations. This is to prevent anybody from creating a new superuser via
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the Trove API.
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Similarly, all list operations include only non-superuser accounts.
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Updatable attributes include username and password.
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We are not going to implement enabling superuser account in this patch set.
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The datastore configuration template had to be updated to enable authentication
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and authorization support (original configuration allowed anonymous
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connections). Default implementations used are:
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* *authenticator: org.apache.cassandra.auth.PasswordAuthenticator*
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* *authorizer: org.apache.cassandra.auth.CassandraAuthorizer*
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The superuser password needs to be changed from the default 'cassandra'
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to a random Trove password which is then stored in a Trove-read-only
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file in '~/.cassandra/cqlshrc' which is also the default location for
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client settings.
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Internal API
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------------
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None
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Guest Agent
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-----------
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The current implementation uses the CQLSH command line client to interface with
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the underlying database. Trove talks to the CQLSH client via the available
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shell and relies on parsing the output of the client to determine the current
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state of the datastore and status of the last operation.
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It also requires Trove to provide the input as a formatted
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(and sanitized) string accepted by the installed version of the client.
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This is not very portable and poses numerous potential compatibility issues in
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the future when the guest agent gets ported to other platforms.
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It also completely bypasses the native exception handling implemented by the
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Python client.
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In order to make the guestagent communicate via the native Python API and
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avoid future portability issues we reimplement the communication interface
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using the the official open-source Python driver for Cassandra.
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The native interface will be implemented in CassandraConnection and
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will also be used to obtain the database status leveraging Python exceptions
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framework.
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User-related functions require having the authorization and authentication
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support enabled on the server. The configuration template will be updated to
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reflect this requirement (see the section on 'Public API Security').
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The following section elaborates on keyspace *("database")* functions.
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Cassandra natively supports row replication. It can store a configurable number
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of copies (replicas) of each row on multiple nodes to ensure reliability and
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fault tolerance. All such replicas are equally important;
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there is no primary or master.
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It supports several replication strategies which determine how the replicated
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rows get distributed across the entire Cassandra cluster.
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The total number of row replicas in a cluster is referred to as the
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replication factor.
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The 'create database' implementation will be using 'SimpleStrategy'
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which is the only strategy that makes sense for a single node setup.
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It is a very simplistic configuration with just a single copy (replica) on
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the guest machine only good for the most basic
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applications and demonstration purposes.
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The following system keyspaces will be by-default excluded from database
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operations and listing by having them included in the 'ignore_dbs' list:
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'system', 'system_auth', 'system_traces'
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Alternatives
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------------
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None
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Implementation
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==============
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Assignee(s)
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-----------
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Petr Malik <pmalik@tesora.com>
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Milestones
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----------
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Liberty-1
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Work Items
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----------
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1. Implement native-driver-based connection for Cassandra datastore.
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2. Enable authentication and authorization on server.
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3. Implement user-function API calls.
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Upgrade Implications
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====================
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The required native Python driver 2.0.x supports Cassandra 1.2 and higher.
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Dependencies
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============
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Trove uses the official open-source Python driver [1]_ for Cassandra
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to connect to the database and execute queries.
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The driver already exists in OpenStack global requirements.
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It does not have to be included in the 'requirements.txt' file, but
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it will need to be added to 'test-requirements.txt' file to enable unit tests.
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The image provider will be required to install it ('cassandra-driver')
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in the Cassandra images.
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The current Trove integration images will be updated to do that.
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Testing
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=======
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Unittests will be added to validate implemented functions and non-trivial
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codepaths.
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Documentation Impact
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====================
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The datastore documentation should be updated to reflect the enabled features.
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References
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==========
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.. [1] Native Python Driver for Cassandra: http://docs.datastax.com/en/developer/python-driver/2.5/common/drivers/introduction/introArchOverview_c.html
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.. [2] Documentation on Cassandra 2.1: http://docs.datastax.com/en/cassandra/2.1/cassandra/gettingStartedCassandraIntro.html
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.. [3] CQL Reference: http://docs.datastax.com/en/cql/3.1/cql/cql_reference/cqlReferenceTOC.html
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