openstack/trove-specs
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trove-specs/specs/liberty/cassandra-database-user-functions.rst
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Change-Id: I6c593dff382a7aac4d758f802173f5a9f1e66182
2020-04-19 11:11:10 +02:00

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Cassandra Database and User Functions

Launchpad blueprint:

https://blueprints.launchpad.net/trove/+spec/cassandra-database-user-functions

Problem Description

The Cassandra datastore currently does not support keyspace1 and user management features.

Proposed Change

The patch set will implement the following keyspace and user related functionality for Cassandra 2.12 datastore:

User Functions:

  • create/delete/get user
  • list users
  • change password
  • grant/revoke/list access
  • update attributes

Keyspace Functions:

  • create/delete database
  • list databases

Configuration

Cassandra stores its configuration in 'cassandra.yaml' file (commonly in '/etc/cassandra'). The node (datastore service) has to be restarted for any changes to the configuration file to take effect. The configuration template will have to be updated to enable authentication and authorization in order to support datastore users and related functions. Client-specific settings (authentication defaults) are stored in '~/.cassandra/cqlshrc' where '~' is the home directory of the Trove user.

Database

None

Public API

None

Public API Security

The current implementation allows original anonymous connections therefore making the datastore wide open for anybody with connection URL. This has to be changed first as the user functions are not even enabled in this setting.

In Cassandra only SUPERUSERS can create other users and grant permissions to database resources. Trove uses the 'cassandra' superuser to perform its administrative tasks. The users it creates are all 'normal' (NOSUPERUSER) accounts. The permissions it can grant are also limited to non-superuser operations. This is to prevent anybody from creating a new superuser via the Trove API. Similarly, all list operations include only non-superuser accounts. Updatable attributes include username and password. We are not going to implement enabling superuser account in this patch set.

The datastore configuration template had to be updated to enable authentication and authorization support (original configuration allowed anonymous connections). Default implementations used are:

  • authenticator: org.apache.cassandra.auth.PasswordAuthenticator
  • authorizer: org.apache.cassandra.auth.CassandraAuthorizer

The superuser password needs to be changed from the default 'cassandra' to a random Trove password which is then stored in a Trove-read-only file in '~/.cassandra/cqlshrc' which is also the default location for client settings.

Python API

None (empty section added after merging)

CLI (python-troveclient)

None (empty section added after merging)

Internal API

None

Guest Agent

The current implementation uses the CQLSH3 command line client to interface with the underlying database. Trove talks to the CQLSH client via the available shell and relies on parsing the output of the client to determine the current state of the datastore and status of the last operation. It also requires Trove to provide the input as a formatted (and sanitized) string accepted by the installed version of the client. This is not very portable and poses numerous potential compatibility issues in the future when the guest agent gets ported to other platforms. It also completely bypasses the native exception handling implemented by the Python client. In order to make the guestagent communicate via the native Python API and avoid future portability issues we reimplement the communication interface using the the official open-source Python driver for Cassandra. The native interface will be implemented in CassandraConnection and will also be used to obtain the database status leveraging Python exceptions framework.

User-related functions require having the authorization and authentication support enabled on the server. The configuration template will be updated to reflect this requirement (see the section on 'Public API Security').

The following section elaborates on keyspace ("database") functions. Cassandra natively supports row replication. It can store a configurable number of copies (replicas) of each row on multiple nodes to ensure reliability and fault tolerance. All such replicas are equally important; there is no primary or master. It supports several replication strategies which determine how the replicated rows get distributed across the entire Cassandra cluster. The total number of row replicas in a cluster is referred to as the replication factor. The 'create database' implementation will be using 'SimpleStrategy' which is the only strategy that makes sense for a single node setup. It is a very simplistic configuration with just a single copy (replica) on the guest machine only good for the most basic applications and demonstration purposes. The following system keyspaces will be by-default excluded from database operations and listing by having them included in the 'ignore_dbs' list: 'system', 'system_auth', 'system_traces'

Alternatives

None

Implementation

Assignee(s)

Petr Malik <pmalik@tesora.com>

Milestones

Liberty-1

Work Items

  1. Implement native-driver-based connection for Cassandra datastore.
  2. Enable authentication and authorization on server.
  3. Implement user-function API calls.

Upgrade Implications

The required native Python driver 2.0.x supports Cassandra 1.2 and higher.

Dependencies

Trove uses the official open-source Python driver4 for Cassandra to connect to the database and execute queries. The driver already exists in OpenStack global requirements. It does not have to be included in the 'requirements.txt' file, but it will need to be added to 'test-requirements.txt' file to enable unit tests. The image provider will be required to install it ('cassandra-driver') in the Cassandra images. The current Trove integration images will be updated to do that.

Testing

Unittests will be added to validate implemented functions and non-trivial codepaths.

Documentation Impact

The datastore documentation should be updated to reflect the enabled features.

References

  1. A keyspace is the outermost container for data in Cassandra, corresponding closely to a relational database.↩︎

  2. Documentation on Cassandra 2.1: http://docs.datastax.com/en/cassandra/2.1/cassandra/gettingStartedCassandraIntro.html↩︎

  3. CQL Reference: http://docs.datastax.com/en/cql/3.1/cql/cql_reference/cqlReferenceTOC.html↩︎

  4. Native Python Driver for Cassandra: http://docs.datastax.com/en/developer/python-driver/2.5/common/drivers/introduction/introArchOverview_c.html↩︎