Hacking on Ceph in Kubernetes with Rook

Warning

This is not official user documentation for setting up production Ceph clusters with Kubernetes. It is aimed at developers who want to hack on Ceph in Kubernetes.

This guide is aimed at Ceph developers getting started with running in a Kubernetes environment. It assumes that you may be hacking on Rook, Ceph or both, so everything is built from source.

1. Build a kubernetes cluster

Before installing Ceph/Rook, make sure you’ve got a working kubernetes cluster with some nodes added (i.e. kubectl get nodes shows you something). The rest of this guide assumes that your development workstation has network access to your kubernetes cluster, such that kubectl works from your workstation.

There are many ways (https://kubernetes.io/docs/setup/pick-right-solution/) to build a kubernetes cluster: here we include some tips/pointers on where to get started.

Host your own

If you already have some linux servers (bare metal or VMs), you can set up your own kubernetes cluster using the kubeadm tool.

https://kubernetes.io/docs/setup/independent/create-cluster-kubeadm/

Here are some tips for a smoother ride with kubeadm:

  • Don’t worry if your servers aren’t powerful: at time of writing, @jcsp is running his home kubernetes cluster on 3 nodes Turion N54L nodes with 8GB RAM.
  • If you have installed any kubernetes/etcd/flannel packages before, make sure they (and their configuration) are erased before you start. kubeadm installs containerised daemons that will be oblivious to any non-containerised services you might already have running.
  • If you have previously added any yum/deb repos for kubernetes packages, disable them before trying to use the packages.cloud.google.com repository. If you don’t, you’ll get quite confusing conflicts.
  • Even if your distro already has docker, make sure you’re installing it a version from docker.com that is within the range mentioned in the kubeadm install instructions. Especially, note that the docker in CentOS 7 will not work.

Hosted elsewhere

If you do not have any servers to hand, you might try a pure container provider such as Google Compute Engine. Your mileage may vary when it comes to what kinds of storage devices are visible to your kubernetes cluster.

Make sure you check how much it’s costing you before you spin up a big cluster!

2. Run a docker repository

Ideally, run this somewhere accessible from both your workstation and your kubernetes cluster (i.e. so that docker push/pull just works everywhere). This is likely to be the same host you’re using as your kubernetes master.

  1. Install the docker-distribution package.
  2. If you want to configure the port, edit /etc/docker-distribution/registry/config.yml
  3. Enable the registry service:
systemctl enable docker-distribution
systemctl start docker-distribution

3. Build Rook

Note

Work within your $GOPATH – here we assume it’s ~/go

Install Go if you don’t already have it.

Download the Rook source code:

go get github.com/rook/rook

# Ignore this warning, as Rook is not a conventional go package
can't load package: package github.com/rook/rook: no Go files in /home/jspray/go/src/github.com/rook/rook

You will now have a Rook source tree in ~/go/src/github.com/rook/rook – you may be tempted to clone it elsewhere, but your life will be easier if you leave it in your GOPATH.

Run make in the root of your Rook tree to build its binaries and containers:

make
...
=== saving image build-9204c79b/ceph-amd64
=== docker build build-9204c79b/ceph-toolbox-base-amd64
sha256:653bb4f8d26d6178570f146fe637278957e9371014ea9fce79d8935d108f1eaa
=== docker build build-9204c79b/ceph-toolbox-amd64
sha256:445d97b71e6f8de68ca1c40793058db0b7dd1ebb5d05789694307fd567e13863
=== caching image build-9204c79b/ceph-toolbox-base-amd64

You can use docker image ls to see the resulting built images. The images you care about are the ones with tags ending “ceph-amd64” (used for the Rook operator and Ceph daemons) and “ceph-toolbox-amd64” (used for the “toolbox” container where the CLI is run).

The rest of this guide assumes that you will want to load your own binaries, and then push the container directly into your docker repository.

4. Build Ceph

It is important that you build Ceph in an environment compatible with the base OS used in the Rook containers. By default, the Rook containers are built with a CentOS base OS. The simplest way to approach this is to build Ceph inside a docker container on your workstation.

You can run a centos docker container with access to your Ceph source tree using a command like:

docker run -i -v /my/ceph/src:/my/ceph/src -t centos:7 /bin/bash

Once you have built Ceph, you can inject the resulting binaries into the Rook container image using the kubejacker.sh script (run from your build directory but from outside your build container).

Setting the $REPO environment variable to your docker repository, execute the script to build a docker image containing your latest Ceph binaries:

build$ REPO=<host>:<port> sh ../src/script/kubejacker/kubejacker.sh

Note

You can also set BASEIMAGE to control that Rook image used as the base – by default this is set to any “ceph-amd64” image.

Now you’ve got your freshly built Rook and freshly built Ceph into a single container image, ready to run. Next time you change something in Ceph, you can re-run this to update your image and restart your kubernetes containers. If you change something in Rook, then re-run the Rook build, and the Ceph build too.

5. Run a Rook cluster

Note

This is just some basic instructions: the Rook documentation is much more expansive, at https://github.com/rook/rook/tree/master/Documentation

The Rook source tree includes example .yaml files in cluster/examples/kubernetes/ceph/. The important ones are:

  • operator.yaml – runs the Rook operator, which will execute any other rook objects we create.
  • cluster.yaml – defines a Ceph cluster
  • toolbox.yaml – runs the toolbox container, which contains the Ceph CLI client.

Copy these into a working directory, and edit as necessary to configure the setup you want:

  • Ensure that the image field in the operator matches the built Ceph image you have uploaded to your Docker repository.
  • Edit the storage section of the cluster: set useAllNodes and useAllDevices to false if you want to create OSDs explicitly using ceph-mgr.

Then, load the configuration into the kubernetes API using kubectl:

kubectl apply -f ./operator.yaml
kubectl apply -f ./cluster.yaml
kubectl apply -f ./toolbox.yaml

Use kubectl -n rook-ceph-system get pods to check the operator pod is coming up, then kubectl -n rook-ceph get pods to check on the Ceph daemons and toolbox. Once everything is up and running, you should be able to open a shell in the toolbox container and run ceph status.

If your mon services start but the rest don’t, it could be that they’re unable to form a quorum due to a Kubernetes networking issue: check that containers in your Kubernetes cluster can ping containers on other nodes.

Cheat sheet

Open a shell in your toolbox container:

kubectl -n rook-ceph exec -it rook-ceph-tools bash

Inspect the Rook operator container’s logs:

kubectl -n rook-ceph-system logs -l app=rook-ceph-operator

Inspect the ceph-mgr container’s logs:

kubectl -n rook-ceph logs -l app=rook-ceph-mgr