Apache Cassandra is a very mature project and there is a lot of information about it on the Internet. However, the information is scattered between different places, and sometimes it's hard to find actual sources of information. This short blog post will help you find the best information.
The most obvious place to go for information about Cassandra is the Apache website. It contains basic information about Cassandra, links to download the distribution, information about community resources (mailing lists, IRC, etc.), and actual documentation.
Another very good source of documentation about Cassandra is DataStax Documentation - although some information described there is DataStax-specific, the documents are very detailed and include architecture guides, reference guides for administrators and developers, and documentation about drivers developed by DataStax (for Java, C++, C#, Node.js, etc.).
Sites under the StackExchange umbrella, like DBA StackExchange & Stack Overflow, could be used to find information about Apache Cassandra. You can search for questions tagged with Cassandra, Cassandra-3.0, tags for drivers, etc. Quite often, the answers to these questions contain a lot of information about particular problems and their resolutions, or about implementation details for given features. Many people answering these questions are well-known Cassandra experts.
The most popular book available for learning Apache Cassandra is "Cassandra: The Definitive Guide, 2nd Edition" by Eben Hewitt & Jeff Carpenter. There are also several books from Packt Publishing and a book from Apress, but they are not as comprehensive (IMHO) as the book from O'Reilly.
DataStax Academy has a number of courses (DS201, DS210, DS220) that explain the foundations of Apache Cassandra (using DSE6 or DSE5 as a base), base operations, and data modeling for Cassandra.
Blogs are the best way to stay up to date on the very latest Apache Cassandra news. There are a number of people and companies that write about Cassandra. To stay on top of all of them, use the Planet Cassandra blog aggregator. It provides a single feed for multiple blogs of people & companies, such as DataStax, ScyllaDB, The Last Pickle, and many others.
The User & Dev Cassandra project mailing lists are also invaluable sources of information. There you can find discussions about the future of the project, features, and various problems and their solutions.
Another way to engage with the community is via Slack. For Cassandra there are several options: Apache Software Foundation (ASF) also has its own Slack instance (you can register at https://s.apache.org/slack-invite), and besides channels for many other Apache projects, it has two channels: #cassandra & #cassandra-dev - for discussion of general usage of Cassandra, and for Cassandra development, correspondingly.
Hopefully, this list will help you navigate the ocean of information about Apache Cassandra. Do you know of a resource that we didn’t list here? Tweet @DataStaxDevs and let us know!