Clients communicating with Apache Cassandra use the Cassandra Query Language (CQL) to issue queries and write data to the cluster. CQL client libraries exist in many languages, and Apache Cassandra ships with a utility called cqlsh that enables you to issue queries against an Apache Cassandra cluster from the command line.
Discovering Endpoints
Once the service is running, you may view information about its endpoints via either of the following methods:
- CLI:
- List endpoint types:
dcos beta-cassandra endpoints - View endpoints for an endpoint type:
dcos beta-cassandra endpoints <endpoint>
- List endpoint types:
- Web:
- List endpoint types:
<dcos-url>/service/cassandra/v1/endpoints - View endpoints for an endpoint type:
<dcos-url>/service/cassandra/v1/endpoints/<endpoint>
- List endpoint types:
By default, the DC/OS Apache Cassandra Service exposes only the native-client endpoint type, which shows the locations for all Cassandra nodes in the cluster. If you have enabled the Thrift protocol in your service configuration, a thrift-client endpoint will also be listed. To see node addresses for use by native clients, such as cqlsh, run dcos beta-cassandra endpoints native-client. A typical response will look like the following:
{
"address": [
"10.0.0.49:9042",
"10.0.2.253:9042",
"10.0.1.27:9042"
],
"dns": [
"node-2-server.cassandra.autoip.dcos.thisdcos.directory:9042",
"node-0-server.cassandra.autoip.dcos.thisdcos.directory:9042",
"node-1-server.cassandra.autoip.dcos.thisdcos.directory:9042"
]
}
In general, the .autoip.dcos.thisdcos.directory endpoints will only work from within the same DC/OS cluster. From outside the cluster you can either use the direct IPs or set up a proxy service that acts as a frontend to your DC/OS Apache Cassandra instance. If you use the IPs, keep in mind that they may change if nodes are moved between machines, whereas the .autoip.dcos.thisdcos.directory hosts will follow the nodes. For development and testing purposes, you can use DC/OS Tunnel to access services from outside the cluster, but this option is not suitable for production use.
Connecting Clients to Endpoints
To connect to a DC/OS Apache Cassandra cluster using cqlsh, first SSH into a host in your DC/OS cluster:
dcos node ssh --leader --master-proxy
Then, use the cassandra Docker image to run cqlsh, passing as an argument the address of one of the Apache Cassandra nodes in the cluster:
docker run cassandra:3.0.13 cqlsh node-0-server.cassandra.autoip.dcos.thisdcos.directory
This will open an interactive shell from which you can issue queries and write to the cluster. To ensure that the cqlsh client and your cluster are using the same CQL version, be sure to use the version of the cassandra Docker image that corresponds to the version of Apache Cassandra being run in your cluster. The version installed by the DC/OS Apache Cassandra Service is 3.0.13.