Multi-node Cassandra Cluster on Kubernetes
You will need to bring your own Kubernetes. A quick and easy way to setup Kubernetes locally is via Docker Compose. Once you have Kubernetes up and running:
./start-cassandra.shThis will create a Kubernetes pod containing a single Cassandra node. You can use the cassandra-status.sh convenience script to see that the node comes up:
./cassandra-status.sh
C* Node Kubernetes Pod
------- --------------
NAME READY STATUS RESTARTS AGE
Up|Normal cassandra-kxa18 1/1 Running 0 1mTo launch more Cassandra nodes and have them join the cluster, simply scale the Cassandra replication controller:
kubectl scale rc cassandra --replicas=2A new pod is created...
./cassandra-status.sh
C* Node Kubernetes Pod
------- --------------
NAME READY STATUS RESTARTS AGE
cassandra-cnvzm 0/1 Image: vyshane/cassandra is ready, container is creating 0 8s
Up|Normal cassandra-kxa18 1/1 Running 0 6m... and it automatically joins the cluster.
./cassandra-status.sh
C* Node Kubernetes Pod
------- --------------
NAME READY STATUS RESTARTS AGE
Up|Joining cassandra-cnvzm 1/1 Running 0 29s
Up|Normal cassandra-kxa18 1/1 Running 0 7m./cassandra-status.sh
C* Node Kubernetes Pod
------- --------------
NAME READY STATUS RESTARTS AGE
Up|Normal cassandra-cnvzm 1/1 Running 0 1m
Up|Normal cassandra-kxa18 1/1 Running 0 8mYou can connect to Cassandra from any pod in the Kubernetes cluster via the IP address of the Cassandra service. To obtain the IP address:
kubectl describe svc cassandraIf the Kubernetes DNS addon is active, you can also connect to the service through the cassandra hostname.
The following environment variables can be configured in the Cassandra replication controller definition:
env:
- name: CASSANDRA_CLUSTER_NAME
value: Cassandra
- name: CASSANDRA_DC
value: DC1
- name: CASSANDRA_RACK
value: Kubernetes Cluster
- name: CASSANDRA_ENDPOINT_SNITCH
value: GossipingPropertyFileSnitchThe Kubernetes project has a Cassandra example that uses a custom seed provider for seed discovery. The example makes use of a Cassandra Docker image from gcr.io/google_containers.
I wanted a solution based on the official Cassandra Docker image. My Docker image extends the official Cassandra image with the addition of dnsutils (for the dig command) and a custom entrypoint that configures seed nodes for the container. Seed node IP addresses are provided via DNS by a headless Kubernetes service.
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