Cassandra

juju deploy cassandra

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Overview

The Apache Cassandra database is the right choice when you need scalability and high availability without compromising performance. Linear scalability and proven fault-tolerance on commodity hardware or cloud infrastructure make it the perfect platform for mission-critical data. Cassandra's support for replicating across multiple datacenters is best-in-class, providing lower latency for your users and the peace of mind of knowing that you can survive regional outages.

See cassandra.apache.org for more information.

Editions

This charm supports Apache Cassandra 2.x and 3.x, and Datastax Enterprise 4.7, 4.8, 5.0, 5.1 & 6.0 The default is Apache Cassandra 3.11.

To use a particular Apache Cassandra release, specify the relevant deb archive in in the install_sources config setting when deploying.

    install_sources:
      - deb http://www.apache.org/dist/cassandra/debian 311 main

To use Datastax Enterprise, set the edition config setting to dse and dse_version to the major version such as "5.1". You also must set the Datastax Enterprise archive URL in install_sources, as the packages require your personal credentials to be downloaded and the URL must include the username and password.

    install_sources:
      - deb http://un:pw@debian.datastax.com/enterprise stable main

Deployment

Cassandra deployments are relatively simple in that they consist of a set of Cassandra nodes which seed from each other to create a ring of servers:

juju deploy -n3 cs:cassandra

The service units will deploy and will form a single ring.

New nodes can be added to scale up:

juju add-unit cassandra

/!\ Nodes must be manually decommissioned before dropping a unit.

juju run --unit cassandra/1 "nodetool decommission"
# Wait until Mode is DECOMMISSIONED
juju run --unit cassandra/1 "nodetool netstats"
juju remove-unit cassandra/1

It is recommended to deploy at least 3 nodes and configure all your keyspaces to have a replication factor of three. Using fewer nodes or neglecting to set your keyspaces' replication settings means that your data is at risk and availability lower, as a failed unit may take the only copy of data with it.

Production systems will normally want to set max_heap_size and heap_newsize to the empty string, to enable automatic memory size tuning. The defaults have been chosen to be suitable for development environments but will perform poorly with real workloads.

Planning

  • Do not attempt to store too much data per node. If you need more space, add more nodes. Most workloads work best with a capacity under 1TB per node, so take care with larger deployments. Recommended capacities are vague and version dependent.

  • You need to keep 50% of your disk space free for Cassandra maintenance operations. If you expect your nodes to hold 500GB of data each, you will need a 1TB partition. Using non-default compaction such as LeveledCompactionStrategy can lower this waste.

  • Much more information can be found in the Cassandra 2.2 documentation

Network Access

The default Cassandra packages are installed from the apache.org archive. To avoid this download, place a copy of the packages in a local archive and specify its location in the install_sources configuration option. The signing key is automatically added.

When using DataStax Enterprise, you need to specify the archive location containing the DataStax Enterprise .deb packages in the install_sources configuration item, and the signing key in the install_keys configuration item. Place the DataStax packages in a local archive to avoid downloading from datastax.com.

Oracle Java SE

While OpenJDK is now supported, it is still often recommended to use Oracle Java SE 8. Unfortunately, this software is accessible only after accepting Oracle's click-through license making deployments using it much more cumbersome. You will need to download the Oracle Java SE 8 Server Runtime for Linux, and place the tarball at a URL accessible to your deployed units. The config item private_jre_url needs to be set to this URL.

Usage

To relate the Cassandra charm to a service that understands how to talk to Cassandra using Thrift or the native Cassandra protocol::

juju deploy cs:~cassandra-charmers/cqlsh
juju add-relation cqlsh cassandra:database

Alternatively, if you require a superuser connection, use the database-admin relation instead of database::

juju deploy cs:~cassandra-charmers/cqlsh cqlsh-admin
juju add-relation cqlsh-admin cassandra:database-admin

Charms using the recommended charms.reactive framework should include 'interface:cassandra' in their layer.yaml. Documentation for using the interface can be seen at https://github.com/stub42/interface-cassandra.

The cluster is configured to use the recommended 'snitch' (GossipingPropertyFileSnitch), so you will need to configure replication of your keyspaces using the NetworkTopologyStrategy replica placement strategy. The datacenter is set in the Cassandra charm configuration, and provided by the client interface if clients need to do this programatically. For example, using the default datacenter named 'juju':

CREATE KEYSPACE IF NOT EXISTS mydata WITH REPLICATION =
{ 'class': 'NetworkTopologyStrategy', 'juju': 3};

Although authentication is configured using the standard PasswordAuthentication, by default no authorization is configured and the provided credentials will have access to all data on the cluster. For more granular permissions, you will need to set the authorizer in the service configuration to CassandraAuthorizer and manually grant permissions to the users.

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Cassandra

DataStax Enterprise