README.md 14 KB
Supported tags and respective Dockerfile links
2.1.16,2.1(2.1/Dockerfile)2.2.8,2.2,2(2.2/Dockerfile)3.0.10,3.0(3.0/Dockerfile)3.9,3,latest(3.9/Dockerfile)
For more information about this image and its history, please see the relevant manifest file (library/cassandra). This image is updated via pull requests to the docker-library/official-images GitHub repo.
For detailed information about the virtual/transfer sizes and individual layers of each of the above supported tags, please see the repos/cassandra/tag-details.md file in the docker-library/repo-info GitHub repo.
What is Cassandra?
Apache Cassandra is an open source distributed database management system designed to handle large amounts of data across many commodity servers, providing high availability with no single point of failure. Cassandra offers robust support for clusters spanning multiple datacenters, with asynchronous masterless replication allowing low latency operations for all clients.
How to use this image
Start a cassandra server instance
Starting a Cassandra instance is simple:
$ docker run --name some-cassandra -d cassandra:tag
... where some-cassandra is the name you want to assign to your container and tag is the tag specifying the Cassandra version you want. See the list above for relevant tags.
Connect to Cassandra from an application in another Docker container
This image exposes the standard Cassandra ports (see the Cassandra FAQ), so container linking makes the Cassandra instance available to other application containers. Start your application container like this in order to link it to the Cassandra container:
$ docker run --name some-app --link some-cassandra:cassandra -d app-that-uses-cassandra
Make a cluster
Using the environment variables documented below, there are two cluster scenarios: instances on the same machine and instances on separate machines. For the same machine, start the instance as described above. To start other instances, just tell each new node where the first is.
$ docker run --name some-cassandra2 -d -e CASSANDRA_SEEDS="$(docker inspect --format='{{ .NetworkSettings.IPAddress }}' some-cassandra)" cassandra:tag
... where some-cassandra is the name of your original Cassandra Server container, taking advantage of docker inspect to get the IP address of the other container.
Or you may use the docker run --link option to tell the new node where the first is:
$ docker run --name some-cassandra2 -d --link some-cassandra:cassandra cassandra:tag
For separate machines (ie, two VMs on a cloud provider), you need to tell Cassandra what IP address to advertise to the other nodes (since the address of the container is behind the docker bridge).
Assuming the first machine's IP address is 10.42.42.42 and the second's is 10.43.43.43, start the first with exposed gossip port:
$ docker run --name some-cassandra -d -e CASSANDRA_BROADCAST_ADDRESS=10.42.42.42 -p 7000:7000 cassandra:tag
Then start a Cassandra container on the second machine, with the exposed gossip port and seed pointing to the first machine:
$ docker run --name some-cassandra -d -e CASSANDRA_BROADCAST_ADDRESS=10.43.43.43 -p 7000:7000 -e CASSANDRA_SEEDS=10.42.42.42 cassandra:tag
Connect to Cassandra from cqlsh
The following command starts another Cassandra container instance and runs cqlsh (Cassandra Query Language Shell) against your original Cassandra container, allowing you to execute CQL statements against your database instance:
$ docker run -it --link some-cassandra:cassandra --rm cassandra sh -c 'exec cqlsh "$CASSANDRA_PORT_9042_TCP_ADDR"'
... or (simplified to take advantage of the /etc/hosts entry Docker adds for linked containers):
$ docker run -it --link some-cassandra:cassandra --rm cassandra cqlsh cassandra
... where some-cassandra is the name of your original Cassandra Server container.
More information about the CQL can be found in the Cassandra documentation.
Container shell access and viewing Cassandra logs
The docker exec command allows you to run commands inside a Docker container. The following command line will give you a bash shell inside your cassandra container:
$ docker exec -it some-cassandra bash
The Cassandra Server log is available through Docker's container log:
$ docker logs some-cassandra
Environment Variables
When you start the cassandra image, you can adjust the configuration of the Cassandra instance by passing one or more environment variables on the docker run command line.
CASSANDRA_LISTEN_ADDRESS
This variable is for controlling which IP address to listen for incoming connections on. The default value is auto, which will set the listen_address option in cassandra.yaml to the IP address of the container as it starts. This default should work in most use cases.
CASSANDRA_BROADCAST_ADDRESS
This variable is for controlling which IP address to advertise to other nodes. The default value is the value of CASSANDRA_LISTEN_ADDRESS. It will set the broadcast_address and broadcast_rpc_address options in cassandra.yaml.
CASSANDRA_RPC_ADDRESS
This variable is for controlling which address to bind the thrift rpc server to. If you do not specify an address, the wildcard address (0.0.0.0) will be used. It will set the rpc_address option in cassandra.yaml.
CASSANDRA_START_RPC
This variable is for controlling if the thrift rpc server is started. It will set the start_rpc option in cassandra.yaml.
CASSANDRA_SEEDS
This variable is the comma-separated list of IP addresses used by gossip for bootstrapping new nodes joining a cluster. It will set the seeds value of the seed_provider option in cassandra.yaml. The CASSANDRA_BROADCAST_ADDRESS will be added the the seeds passed in so that the sever will talk to itself as well.
CASSANDRA_CLUSTER_NAME
This variable sets the name of the cluster and must be the same for all nodes in the cluster. It will set the cluster_name option of cassandra.yaml.
CASSANDRA_NUM_TOKENS
This variable sets number of tokens for this node. It will set the num_tokens option of cassandra.yaml.
CASSANDRA_DC
This variable sets the datacenter name of this node. It will set the dc option of cassandra-rackdc.properties.
CASSANDRA_RACK
This variable sets the rack name of this node. It will set the rack option of cassandra-rackdc.properties.
CASSANDRA_ENDPOINT_SNITCH
This variable sets the snitch implementation this node will use. It will set the endpoint_snitch option of cassandra.yml.
Caveats
Where to Store Data
Important note: There are several ways to store data used by applications that run in Docker containers. We encourage users of the cassandra images to familiarize themselves with the options available, including:
- Let Docker manage the storage of your database data by writing the database files to disk on the host system using its own internal volume management. This is the default and is easy and fairly transparent to the user. The downside is that the files may be hard to locate for tools and applications that run directly on the host system, i.e. outside containers.
- Create a data directory on the host system (outside the container) and mount this to a directory visible from inside the container. This places the database files in a known location on the host system, and makes it easy for tools and applications on the host system to access the files. The downside is that the user needs to make sure that the directory exists, and that e.g. directory permissions and other security mechanisms on the host system are set up correctly.
The Docker documentation is a good starting point for understanding the different storage options and variations, and there are multiple blogs and forum postings that discuss and give advice in this area. We will simply show the basic procedure here for the latter option above:
- Create a data directory on a suitable volume on your host system, e.g.
/my/own/datadir. Start your
cassandracontainer like this:$ docker run --name some-cassandra -v /my/own/datadir:/var/lib/cassandra -d cassandra:tag
The -v /my/own/datadir:/var/lib/cassandra part of the command mounts the /my/own/datadir directory from the underlying host system as /var/lib/cassandra inside the container, where Cassandra by default will write its data files.
Note that users on host systems with SELinux enabled may see issues with this. The current workaround is to assign the relevant SELinux policy type to the new data directory so that the container will be allowed to access it:
$ chcon -Rt svirt_sandbox_file_t /my/own/datadir
No connections until Cassandra init completes
If there is no database initialized when the container starts, then a default database will be created. While this is the expected behavior, this means that it will not accept incoming connections until such initialization completes. This may cause issues when using automation tools, such as docker-compose, which start several containers simultaneously.
Supported Docker versions
This image is officially supported on Docker version 1.12.5.
Support for older versions (down to 1.6) is provided on a best-effort basis.
Please see the Docker installation documentation for details on how to upgrade your Docker daemon.
User Feedback
Issues
If you have any problems with or questions about this image, please contact us through a GitHub issue. If the issue is related to a CVE, please check for a cve-tracker issue on the official-images repository first.
You can also reach many of the official image maintainers via the #docker-library IRC channel on Freenode.
Contributing
You are invited to contribute new features, fixes, or updates, large or small; we are always thrilled to receive pull requests, and do our best to process them as fast as we can.
Before you start to code, we recommend discussing your plans through a GitHub issue, especially for more ambitious contributions. This gives other contributors a chance to point you in the right direction, give you feedback on your design, and help you find out if someone else is working on the same thing.
Documentation
Documentation for this image is stored in the cassandra/ directory of the docker-library/docs GitHub repo. Be sure to familiarize yourself with the repository's README.md file before attempting a pull request.