cockroachdb

CockroachDB on Kubernetes as a StatefulSet

This example deploys CockroachDB on Kubernetes as a StatefulSet. CockroachDB is a distributed, scalable NewSQL database. Please see the homepage and the documentation for details.

Limitations

StatefulSet limitations

Standard StatefulSet limitations apply: There is currently no possibility to use node-local storage (outside of single-node tests), and so there is likely a performance hit associated with running CockroachDB on some external storage. Note that CockroachDB already does replication and thus it is unnecessary to deploy it onto persistent volumes which already replicate internally. For this reason, high-performance use cases on a private Kubernetes cluster may want to consider a DaemonSet deployment until Stateful Sets support node-local storage (see #7562).

Recovery after persistent storage failure

A persistent storage failure (e.g. losing the hard drive) is gracefully handled by CockroachDB as long as enough replicas survive (two out of three by default). Due to the bootstrapping in this deployment, a storage failure of the first node is special in that the administrator must manually prepopulate the "new" storage medium by running an instance of CockroachDB with the --join parameter. If this is not done, the first node will bootstrap a new cluster, which will lead to a lot of trouble.

Dynamic volume provisioning

The deployment is written for a use case in which dynamic volume provisioning is available. When that is not the case, the persistent volume claims need to be created manually. See minikube.sh for the necessary steps. If you're on GCE or AWS, where dynamic provisioning is supported, no manual work is needed to create the persistent volumes.

Testing locally on minikube

Follow the steps in minikube.sh (or simply run that file).

Testing in the cloud on GCE or AWS

Once you have a Kubernetes cluster running, just run kubectl create -f cockroachdb-statefulset.yaml to create your cockroachdb cluster. This works because GCE and AWS support dynamic volume provisioning by default, so persistent volumes will be created for the CockroachDB pods as needed.

Accessing the database

Along with our StatefulSet configuration, we expose a standard Kubernetes service that offers a load-balanced virtual IP for clients to access the database with. In our example, we've called this service cockroachdb-public.

Start up a client pod and open up an interactive, (mostly) Postgres-flavor SQL shell using:

$ kubectl run -it --rm cockroach-client --image=cockroachdb/cockroach --restart=Never --command -- ./cockroach sql --host cockroachdb-public --insecure

You can see example SQL statements for inserting and querying data in the included demo script, but can use almost any Postgres-style SQL commands. Some more basic examples can be found within CockroachDB's documentation.

Accessing the admin UI

If you want to see information about how the cluster is doing, you can try pulling up the CockroachDB admin UI by port-forwarding from your local machine to one of the pods:

kubectl port-forward cockroachdb-0 8080

Once you’ve done that, you should be able to access the admin UI by visiting http://localhost:8080/ in your web browser.

Simulating failures

When all (or enough) nodes are up, simulate a failure like this:

kubectl exec cockroachdb-0 -- /bin/bash -c "while true; do kill 1; done"

You can then reconnect to the database as demonstrated above and verify that no data was lost. The example runs with three-fold replication, so it can tolerate one failure of any given node at a time. Note also that there is a brief period of time immediately after the creation of the cluster during which the three-fold replication is established, and during which killing a node may lead to unavailability.

The demo script gives an example of killing one instance of the database and ensuring the other replicas have all data that was written.

Scaling up or down

Scale the Stateful Set by running

kubectl scale statefulset cockroachdb --replicas=4

Note that you may need to create a new persistent volume claim first. If you ran minikube.sh, there's a spare volume so you can immediately scale up by one. If you're running on GCE or AWS, you can scale up by as many as you want because new volumes will automatically be created for you. Convince yourself that the new node immediately serves reads and writes.

Cleaning up when you're done

Because all of the resources in this example have been tagged with the label app=cockroachdb, we can clean up everything that we created in one quick command using a selector on that label:

kubectl delete statefulsets,persistentvolumes,persistentvolumeclaims,services,poddisruptionbudget -l app=cockroachdb