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Accessing Cassandra

This guide explains how to access a running KUDO Cassandra instance from your application deployed within the same Kubernetes cluster.

⚠️ The KUDO Cassandra operator currently does not support accessing the Cassandra instance from outside of the same Kubernetes cluster.

Pre-conditions

  • KUDO Cassandra instance running
  • KUDO CLI installed

Steps

Preparation

1. Set the shell variables

The examples below assume that the instance and namespace names are stored in the following shell variables. With this assumptions met, you should be able to copy-paste the commands easily.

instance_name=cassandra
namespace_name=default

2. Verify that the variables are set correctly

kubectl get instance $instance_name -n $namespace_name

Example output:

NAME        AGE
cassandra   16h

Access Cassandra

You will run simple cqlsh command within an ephemeral pod on the Kubernetes cluster to show how to connect to Cassandra.

3. Retrieve the docker image name

In order to run cqlsh you need a container image which has it. For simplicity, you can use the same image which is used by the cassandra nodes. Run the following command to retrieve its full name:

cassandra_image=$(kubectl get pod -n ${namespace_name} ${instance_name}-node-0 --template '{{ (index .spec.containers 0).image }}{{"\n"}}')
echo ${cassandra_image}

Example output:

mesosphere/cassandra:3.11.6-1.0.0

4. Run a command which accesses cassandra in a pod

This command illustrates what DNS name to use to connect to Cassandra:

kubectl run --wait cassandra-access-demo --image=${cassandra_image} --restart=Never -- \
 cqlsh --execute "describe cluster" ${instance_name}-svc.${namespace_name}.svc.cluster.local

Expected output:

pod/cassandra-access-demo created

5. Retrieve the output

Once the pod completes (which should take no more than a few seconds), you can see its output using a command such as the following:

kubectl logs cassandra-access-demo

Example output:

Warning: Cannot create directory at `/home/cassandra/.cassandra`. Command history will not be saved.


Cluster: cassandra1
Partitioner: Murmur3Partitioner

Cleanup

6. Delete the ephemeral pod

kubectl delete pod cassandra-access-demo

Expected output:

pod "cassandra-access-demo" deleted

Access from outside the Cluster

The operator supports creation of a service that opens up ports to access Cassandra from outside the cluster. To enable this, you have to set the following variables:

kubectl kudo update $instance_name -n $namespace_name -p EXTERNAL_NATIVE_TRANSPORT=true

This will create a service with a LoadBalancer port that forwards to the Cassandra nodes. There are the following options:

  • EXTERNAL_NATIVE_TRANSPORT="true" Enable access to the cluster from the outside
  • EXTERNAL_RPC="true" Enable access to the legacy RPC port if it's enabled on the cluster (Requires that START_RPC is "true")
  • EXTERNAL_NATIVE_TRANSPORT_PORT="9042" The external port that is forwarded to the native transport port on the nodes
  • EXTERNAL_RPC_PORT="9160" The external port that is forwarded to the rpc port on the nodes
  • EXTERNAL_SERVICE_ANNOTATIONS Annotations that are added to the external service. E.g., this can be used to configure ExternalDNS access

⚠️ The external service definition will at the moment not be deleted if you set EXTERNAL_NATIVE_TRANSPORT and EXTERNAL_RPC to "false". If you need to remove external access, you have to remove the external service manually.

ExternalDNS annotations

The EXTERNAL_SERVICE_ANNOTATIONS parameter can be used to set up ExternalDNS access when the external service is enabled. For example, one can set

EXTERNAL_SERVICE_ANNOTATIONS={"external-dns.alpha.kubernetes.io/hostname": "cassandra.example.org"}