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Installing Ceph Storage with Rook

In this tutorial you'll create a Ceph storage for k0s. Ceph is a highly scalable, distributed storage solution. It offers object, block, and file storage, and it's designed to run on any common hardware. Ceph implements data replication into multiple volumes that makes it fault-tolerant. Another clear advantage of Ceph in Kubernetes is the dynamic provisioning. This means that applications just need to request the storage (persistent volume claim) and Ceph will automatically provision the requested storage without a manual creation of the persistent volume each time.

Unfortunately, the Ceph deployment as such can be considered a bit complex. To make the deployment easier, we'll use Rook operator. Rook is a CNCF project and it's dedicated to storage orchestration. Rook supports several storage solutions, but in this tutorial we will use it to manage Ceph.

This tutorial uses three worker nodes and one controller. It's possible to use less nodes, but using three worker nodes makes it a good example for deploying a high-available storage cluster. We use external storage partitions, which are assigned to the worker nodes to be used by Ceph.

After the Ceph deployment we'll deploy a sample application (MongoDB) to use the storage in practice.

k0s_rook_ceph_cluster.png

Prerequisites

  • Linux OS
  • GitHub access
  • AWS account
  • Terraform

Deployment steps

1. Preparations

In this example we'll use Terraform to create four Ubuntu VMs on AWS. Using Terraform makes the VM deployment fast and repeatable. You can avoid manually setting up everything in the AWS GUI. Moreover, when you have finished with the tutorial, it's very easy to tear down the VMs with Terraform (with one command). However, you can set up the nodes in many different ways and it doesn't make a difference in the following steps.

We will use k0sctl to create the k0s cluster. k0sctl repo also includes a ready-made Terraform configuration to create the VMs on AWS. We'll use that. Let's start be cloning the k0sctl repo.

git clone [email protected]:k0sproject/k0sctl.git

Take a look at the Terraform files

cd k0sctl/examples/aws-tf
ls -l

Open variables.tf and set the number of controller and worker nodes like this:

variable "cluster_name" {
  type    = string
  default = "k0sctl"
}

variable "controller_count" {
  type    = number
  default = 1
}

variable "worker_count" {
  type    = number
  default = 3
}

variable "cluster_flavor" {
  type    = string
  default = "t3.small"
}

Open main.tf to check or modify k0s version near the end of the file.

You can also configure a different name to your cluster and change the default VM type. t3.small (2 vCPUs, 2 GB RAM) runs just fine for this tutorial.

2. Create the VMs

For AWS, you need an account. Terraform will use the following environment variable: AWS_ACCESS_KEY_ID, AWS_SECRET_ACCESS_KEY, AWS_SESSION_TOKEN. You can easily copy-paste them from the AWS portal. For more information, see the AWS documentation.

k0s_rook_ceph_aws_credentials.png

When the environment variables are set, you can proceed with Terraform and deploy the VMs.

terraform init
terraform apply

If you decide to create the VMs manually using AWS GUI, you need to disable source / destination checking. This needs to be disbled always for multi-node Kubernetes clusters in order to get the node-to-node communication working due to Network Address Translation. For Terraform this is already taken care of in the default configuration.

3. Create and attach the volumes

Ceph requires one of the following storage options for storing the data:

  • Raw devices (no partitions or formatted filesystems)
  • Raw partitions (no formatted filesystem)
  • PVs available from a storage class in block mode

We will be using raw partititions (AWS EBS volumes), which can be easily attached to the worker node VMs. They are automatically detected by Ceph with its default configuration.

Deploy AWS EBS volumes, one for each worker node. You can manually create three EBS volumes (for example 10 GB each) using the AWS GUI and attach those to your worker nodes. Formatting shouldn't be done. Instead, Ceph handles that part automatically.

After you have attached the EBS volumes to the worker nodes, log in to one of the workers and check the available block devices:

lsblk -f
NAME        FSTYPE   LABEL           UUID                                 FSAVAIL FSUSE% MOUNTPOINT
loop0       squashfs                                                            0   100% /snap/amazon-ssm-agent/3552
loop1       squashfs                                                            0   100% /snap/core18/1997
loop2       squashfs                                                            0   100% /snap/snapd/11588
loop3       squashfs                                                            0   100% /snap/lxd/19647
nvme0n1
└─nvme0n1p1 ext4     cloudimg-rootfs e8070c31-bfee-4314-a151-d1332dc23486    5.1G    33% /
nvme1n1

The last line (nvme1n1) in this example printout corresponds to the attached EBS volume. Note that it doesn't have any filesystem (FSTYPE is empty). This meets the Ceph storage requirements and you are good to proceed.

4. Install k0s using k0sctl

You can use terraform to automatically output a config file for k0sctl with the ip addresses and access details.

terraform output -raw k0s_cluster > k0sctl.yaml

After that deploying k0s becomes very easy with the ready-made configuration.

k0sctl apply --config k0sctl.yaml

It might take around 2-3 minutes for k0sctl to connect each node, install k0s and connect the nodes together to form a cluster.

5. Access k0s cluster

To access your new cluster remotely, you can use k0sctl to fetch kubeconfig and use that with kubectl or Lens.

k0sctl kubeconfig --config k0sctl.yaml > kubeconfig
export KUBECONFIG=$PWD/kubeconfig
kubectl get nodes

The other option is to login to your controller node and use the k0s in-built kubectl to access the cluster. Then you don't need to worry about kubeconfig (k0s takes care of that automatically).

ssh -i aws.pem <username>@<ip-address>
sudo k0s kubectl get nodes

6. Deploy Rook

To get started with Rook, let's first clone the Rook GitHub repo:

git clone --single-branch --branch release-1.7 https://github.com/rook/rook.git
cd rook/cluster/examples/kubernetes/ceph

We will use mostly the default Rook configuration. However, k0s kubelet drectory must be configured in operator.yaml like this

ROOK_CSI_KUBELET_DIR_PATH: "/var/lib/k0s/kubelet"

To create the resources, which are needed by the Rook’s Ceph operator, run

kubectl apply -f crds.yaml -f common.yaml -f operator.yaml

Now you should see the operator running. Check them with

kubectl get pods -n rook-ceph

7. Deploy Ceph Cluster

Then you can proceed to create a Ceph cluster. Ceph will use the three EBS volumes attached to the worker nodes:

kubectl apply -f cluster.yaml

It takes some minutes to prepare the volumes and create the cluster. Once this is completed you should see the following output:

kubectl get pods -n rook-ceph
NAME                                                         READY   STATUS      RESTARTS   AGE
csi-cephfsplugin-nhxc8                                       3/3     Running     0          2m48s
csi-cephfsplugin-provisioner-db45f85f5-ldhjp                 6/6     Running     0          2m48s
csi-cephfsplugin-provisioner-db45f85f5-sxfm8                 6/6     Running     0          2m48s
csi-cephfsplugin-tj2bh                                       3/3     Running     0          2m48s
csi-cephfsplugin-z2rrl                                       3/3     Running     0          2m48s
csi-rbdplugin-5q7gq                                          3/3     Running     0          2m49s
csi-rbdplugin-8sfpd                                          3/3     Running     0          2m49s
csi-rbdplugin-f2xdz                                          3/3     Running     0          2m49s
csi-rbdplugin-provisioner-d85cbdb48-g6vck                    6/6     Running     0          2m49s
csi-rbdplugin-provisioner-d85cbdb48-zpmvr                    6/6     Running     0          2m49s
rook-ceph-crashcollector-ip-172-31-0-76-64cb4c7775-m55x2     1/1     Running     0          45s
rook-ceph-crashcollector-ip-172-31-13-183-654b46588d-djqsd   1/1     Running     0          2m57s
rook-ceph-crashcollector-ip-172-31-15-5-67b68698f-gcjb7      1/1     Running     0          2m46s
rook-ceph-mgr-a-5ffc65c874-8pxgv                             1/1     Running     0          58s
rook-ceph-mon-a-ffcd85c5f-z89tb                              1/1     Running     0          2m59s
rook-ceph-mon-b-fc8f59464-lgczk                              1/1     Running     0          2m46s
rook-ceph-mon-c-69bd87b558-kl4nl                             1/1     Running     0          91s
rook-ceph-operator-54cf7487d4-pl66p                          1/1     Running     0          4m57s
rook-ceph-osd-0-dd4fd8f6-g6s9m                               1/1     Running     0          48s
rook-ceph-osd-1-7c478c49c4-gkqml                             1/1     Running     0          47s
rook-ceph-osd-2-5b887995fd-26492                             1/1     Running     0          46s
rook-ceph-osd-prepare-ip-172-31-0-76-6b5fw                   0/1     Completed   0          28s
rook-ceph-osd-prepare-ip-172-31-13-183-cnkf9                 0/1     Completed   0          25s
rook-ceph-osd-prepare-ip-172-31-15-5-qc6pt                   0/1     Completed   0          23s

8. Configure Ceph block storage

Before Ceph can provide storage to your cluster, you need to create a ReplicaPool and a StorageClass. In this example, we use the default configuration to create the block storage.

kubectl apply -f ./csi/rbd/storageclass.yaml

9. Request storage

Create a new manifest file mongo-pvc.yaml with the following content:

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: mongo-pvc
spec:
  storageClassName: rook-ceph-block
  accessModes:
  - ReadWriteOnce
  resources:
    requests:
      storage: 2Gi

This will create Persistent Volume Claim (PVC) to request a 2 GB block storage from Ceph. Provioning will be done dynamically. You can define the block size freely as long as it fits to the available storage size.

kubectl apply -f mongo-pvc.yaml

You can now check the status of your PVC:

kubectl get pvc

When the PVC gets the requested volume reserved (bound), it should look like this:

kubectl get pvc
NAME        STATUS   VOLUME                                     CAPACITY   ACCESS MODES   STORAGECLASS      AGE
mongo-pvc   Bound    pvc-08337736-65dd-49d2-938c-8197a8871739   2Gi        RWO            rook-ceph-block   6s

10. Deploy an example application

Let's deploy a Mongo database to verify the Ceph storage. Create a new file mongo.yaml with the following content:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: mongo
spec:
  selector:
    matchLabels:
      app: mongo
  template:
    metadata:
      labels:
        app: mongo
    spec:
      containers:
      - image: mongo:4.0
        name: mongo
        ports:
        - containerPort: 27017
          name: mongo
        volumeMounts:
        - name: mongo-persistent-storage
          mountPath: /data/db
      volumes:
      - name: mongo-persistent-storage
        persistentVolumeClaim:
          claimName: mongo-pvc

Deploy the database:

kubectl apply -f mongo.yaml

11. Access the application

Open the MongoDB shell using the mongo pod:

kubectl get pods
NAME                    READY   STATUS    RESTARTS   AGE
mongo-b87cbd5cc-4wx8t   1/1     Running   0          76s
kubectl exec -it mongo-b87cbd5cc-4wx8t -- mongo

Create a DB and insert some data:

> use testDB
switched to db testDB
> db.testDB.insertOne( {name: "abc", number: 123  })
{
  "acknowledged" : true,
  "insertedId" : ObjectId("60815690a709d344f83b651d")
}
> db.testDB.insertOne( {name: "bcd", number: 234  })
{
  "acknowledged" : true,
  "insertedId" : ObjectId("6081569da709d344f83b651e")
}

Read the data:

> db.getCollection("testDB").find()
{ "_id" : ObjectId("60815690a709d344f83b651d"), "name" : "abc", "number" : 123 }
{ "_id" : ObjectId("6081569da709d344f83b651e"), "name" : "bcd", "number" : 234 }
>

You can also try to restart the mongo pod or restart the worker nodes to verity that the storage is persistent.

12. Clean-up

You can use Terraform to take down the VMs:

terraform destroy

Remember to delete the EBS volumes separately.

Conclusions

You have now created a replicated Ceph storage for k0s. All you data is stored to multiple disks at the same time so you have a fault-tolerant solution. You also have enabled dynamic provisioning. Your applications can request the available storage without a manual creation of the persistent volumes each time.

This was just one example to deploy distributed storage to k0s cluster using an operator. You can easily use different Kubernetes storage solutions with k0s.