CockroachDB is a distributed SQL database designed for scalability, resilience, and ease of deployment. It is increasingly common for businesses to use a hybrid deployment model where a part of their database cluster is in a cloud Kubernetes cluster while another part resides on-premise for various compliance, performance, or cost reasons. This article explains how to add an on-premise CockroachDB node to an existing cluster hosted on Kubernetes.

Understanding the Basic Requirements

Firstly, it is crucial to understand the network requirements. In order to add an on-premise node to a Kubernetes-hosted CockroachDB cluster, the node must be able to communicate with the Kubernetes pods. This typically involves setting up a secure and reliable network connection between the on-premise environment and the cloud environment housing the Kubernetes cluster.

You'll also need:

1. A running CockroachDB cluster on Kubernetes.
2. An on-premise server or VM with a Unix-like OS installed.
3. Appropriate network permissions to ensure connections can be made between the Kubernetes nodes and the on-premise server.

Configuring the On-premise Node

Let's start by setting up the on-premise CockroachDB node. First, install CockroachDB on your local system. This can involve downloading the binary directly from the CockroachDB site and installing it using their provided instructions.

Step 1: Download and Install CockroachDB

wget -qO- https://binaries.cockroachdb.com/cockroach-v21.2.10.linux-amd64.tgz | tar  xvz
cp -i cockroach-v21.2.10.linux-amd64/cockroach /usr/local/bin/

Step 2: Start the CockroachDB Node

You need to start the node with the --join flag pointing it to the Kubernetes-hosted cluster nodes. You will also need to include the --advertise-addr flag to specify the reachable address of the on-premise node.

cockroach start --insecure --store=node1 --listen-addr=localhost:26257 --http-addr=localhost:8080 --join=<k8s-node-address> --advertise-addr=<on-premise-node-IP>

Replace <k8s-node-address> with the IP address of one of your Kubernetes nodes running a CockroachDB instance, and <on-premise-node-IP> with the external IP of your on-premise server.

Configuring Kubernetes

To ensure the Kubernetes cluster acknowledges the new node, further configuration might be necessary, particularly around network policies and ingress or egress rules, depending on your security setup.

Creating Appropriate Firewall Rules

Ensure your cloud provider's firewall (and any local firewalls) are configured to allow traffic on the relevant ports (usually TCP 26257 and TCP 8080) between your on-premise node and the Kubernetes nodes.

Ensuring Data Consistency

After setting up the connection, it’s imperative to monitor the data consistency across your hybrid cluster setup. CockroachDB's inherently strong consistency model will help ensure that even with geographically distributed nodes, your transactions are atomic and linearizable.

Monitoring and Management

Lastly, adopt monitoring tools like Prometheus or Grafana, which can integrate well with both Kubernetes and CockroachDB to provide insights and alerts regarding the health and performance of your cluster.

Summary Table

Conclusion

Adding an on-premise node to a Kubernetes-hosted CockroachDB cluster primarily requires careful planning around networking and security, followed by correct configuration of both the on-premise node and Kubernetes settings. By ensuring these aspects are addressed, businesses can leverage the strengths of both on-premise and cloud architectures in a harmonious, efficient manner.