This tutorial shows you how to develop a native cloud Cassandra deployment on Kubernetes. In this instance, a custom Cassandra SeedProvider
enables Cassandra to discover new Cassandra nodes as they join the cluster.
Deploying stateful distributed applications, like Cassandra, within a clustered environment can be challenging. StatefulSets greatly simplify this process. Please read about StatefulSets for more information about the features used in this tutorial.
Cassandra Docker
The Pods use the gcr.io/google-samples/cassandra:v13
image from Google’s container registry.
The docker image above is based on debian-base and includes OpenJDK 8. This image includes a standard Cassandra installation from the Apache Debian repo. By using environment variables you can change values that are inserted into cassandra.yaml
.
ENV VAR | DEFAULT VALUE |
---|---|
CASSANDRA_CLUSTER_NAME | ‘Test Cluster’ |
CASSANDRA_NUM_TOKENS | 32 |
CASSANDRA_RPC_ADDRESS | 0.0.0.0 |
To complete this tutorial, you should already have a basic familiarity with Pods, Services, and StatefulSets. In addition, you should:
Install and Configure the kubectl
command line
Download cassandra-service.yaml and cassandra-statefulset.yaml
Have a supported Kubernetes Cluster running
Note: Please read the getting started guides if you do not already have a cluster.
Caution: Minikube defaults to 1024MB of memory and 1 CPU which results in an insufficient resource errors during this tutorial.
To avoid these errors, run minikube with:
minikube start --memory 5120 --cpus=4
A Kubernetes Service describes a set of Pods that perform the same task.
The following Service
is used for DNS lookups between Cassandra Pods and clients within the Kubernetes Cluster.
Create a Service
to track all Cassandra StatefulSet Nodes from the cassandra-service.yaml
file:
kubectl create -f cassandra-service.yaml
cassandra/cassandra-service.yaml docs/tutorials/stateful-application/cassandra
|
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|
Get the Cassandra Service
.
kubectl get svc cassandra
The response should be
NAME CLUSTER-IP EXTERNAL-IP PORT(S) AGE
cassandra None <none> 9042/TCP 45s
If anything else returns, the service was not successfully created. Read Debug Services for common issues.
The StatefulSet manifest, included below, creates a Cassandra ring that consists of three Pods.
Note: This example uses the default provisioner for Minikube. Please update the following StatefulSet for the cloud you are working with.
Create the Cassandra StatefulSet from the cassandra-statefulset.yaml
file:
kubectl create -f cassandra-statefulset.yaml
cassandra/cassandra-statefulset.yaml docs/tutorials/stateful-application/cassandra
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Get the Cassandra StatefulSet:
kubectl get statefulset cassandra
The response should be
NAME DESIRED CURRENT AGE
cassandra 3 0 13s
The StatefulSet resource deploys Pods sequentially.
Get the Pods to see the ordered creation status:
kubectl get pods -l=“app=cassandra”
The response should be
NAME READY STATUS RESTARTS AGE
cassandra-0 1/1 Running 0 1m
cassandra-1 0/1 ContainerCreating 0 8s
Note: It can take up to ten minutes for all three Pods to deploy.
Once all Pods are deployed, the same command returns:
NAME READY STATUS RESTARTS AGE
cassandra-0 1/1 Running 0 10m
cassandra-1 1/1 Running 0 9m
cassandra-2 1/1 Running 0 8m
Run the Cassandra utility nodetool to display the status of the ring.
kubectl exec cassandra-0 – nodetool status
The response is:
Datacenter: DC1-K8Demo
======================
Status=Up/Down
|/ State=Normal/Leaving/Joining/Moving
-- Address Load Tokens Owns (effective) Host ID Rack
UN 172.17.0.5 83.57 KiB 32 74.0% e2dd09e6-d9d3-477e-96c5-45094c08db0f Rack1-K8Demo
UN 172.17.0.4 101.04 KiB 32 58.8% f89d6835-3a42-4419-92b3-0e62cae1479c Rack1-K8Demo
UN 172.17.0.6 84.74 KiB 32 67.1% a6a1e8c2-3dc5-4417-b1a0-26507af2aaad Rack1-K8Demo
Use kubectl edit
to modify the size of a Cassandra StatefulSet.
Run the following command:
kubectl edit statefulset cassandra
This command opens an editor in your terminal. The line you need to change is the replicas
field.
Note: The following sample is an excerpt of the StatefulSet file.
# Please edit the object below. Lines beginning with a '#' will be ignored,
# and an empty file will abort the edit. If an error occurs while saving this file will be
# reopened with the relevant failures.
#
apiVersion: apps/v1 # for versions before 1.9.0 use apps/v1beta2
kind: StatefulSet
metadata:
creationTimestamp: 2016-08-13T18:40:58Z
generation: 1
labels:
app: cassandra
name: cassandra
namespace: default
resourceVersion: "323"
selfLink: /apis/apps/v1/namespaces/default/statefulsets/cassandra
uid: 7a219483-6185-11e6-a910-42010a8a0fc0
spec:
replicas: 3
The StatefulSet now contains 4 Pods.
Get the Cassandra StatefulSet to verify:
kubectl get statefulset cassandra
The response should be
NAME DESIRED CURRENT AGE
cassandra 4 4 36m
Deleting or scaling a StatefulSet down does not delete the volumes associated with the StatefulSet. This ensures safety first: your data is more valuable than an auto purge of all related StatefulSet resources.
Warning: Depending on the storage class and reclaim policy, deleting the Persistent Volume Claims may cause the associated volumes to also be deleted. Never assume you’ll be able to access data if its volume claims are deleted.
Run the following commands to delete everything in a StatefulSet
:
grace=$(kubectl get po cassandra-0 -o=jsonpath=‘{.spec.terminationGracePeriodSeconds}’)
&& kubectl delete statefulset -l app=cassandra
&& echo “Sleeping $grace”
&& sleep $grace
&& kubectl delete pvc -l app=cassandra
Run the following command to delete the Cassandra Service
.
kubectl delete service -l app=cassandra