Prometheus is the mostly widely used application for scraping cloud native application metrics. Prometheus and OpenEBS together provide a complete open source stack for monitoring. In this solution, OpenEBS is used as Prometheus TSDB, where all the metrics are permanently stored on local Kubernetes cluster.
When using OpenEBS as TSDB, following are the advantages:
All the data is stored locally and managed natively to Kubernetes
No need of externally managed Prometheus storage
Start with small storage and expand the size of TSDB as needed on the fly
Prometheus metrics are highly available. When a node fails or rebooted, Prometheus pod is rescheduled onto on of the two other nodes where cStor volume replica is available. The metrics data is rebuilt when the node becomes available
Take backup of the Prometheus metrics periodically and back them up to S3 or any object storage so that restoration of the same metrics is possible to the same or any other Kubernetes cluster
As shown above, OpenEBS volumes need to be configured with three replicas for high availability. This configuration work fine when the nodes (hence the cStor pool) is deployed across Kubernetes zones.
Install OpenEBS : If OpenEBS is not installed on the Kubernetes already, start by installing OpenEBS on all or some of the cluster nodes. If OpenEBS is already installed, go to step 2.
Configure cStor Pool : After OpenEBS installation, cStor pool has to be configured. As prometheus TSDB needs high availability of data, OpenEBS cStor volume has to be configured with three replicas. During cStor Pool creation, make sure that the maxPools parameter is set to >=3. If cStor Pool is already configured as required go to Step 4 to create Prometheus StorageClass.
Create Storage Class :
StorageClass is the interface through which most of the OpenEBS storage policies are defined. See Prometheus Storage Class section below.
Configure PVC : Prometheus needs only one volume to store the data. See PVC example spec below.
Launch and test Prometheus:
kubectl apply -f <prometheus.yaml>to see Prometheus running. For more information on configuring more services to be monitored, see Prometheus documentation.
helm install stable/prometheus --storage-class=< openebs-cstor-3replica >
Persistent volume for Grafana:
Grafana needs a much smaller persistent storage for storing metadata. Typically the storage class used for Prometheus is reused for Grafana as well. Just construct a new PVC with smaller storage size.
A live deployment of Prometheus using OpenEBS volumes as highly available TSDB storage can be seen at the website www.openebs.ci
Deployment YAML spec files for Prometheus and OpenEBS resources are found here
Post deployment Operations
Monitor OpenEBS Volume size
It is not seamless to increase the cStor volume size (refer to the roadmap item). Hence, it is recommended that sufficient size is allocated during the initial configuration.
Monitor cStor Pool size
As in most cases, cStor pool may not be dedicated to just Prometheus alone. It is recommended to watch the pool capacity and add more disks to the pool before it hits 80% threshold. See cStorPool metrics
Maintain volume replica quorum during node upgrades
cStor volume replicas need to be in quorum Prometheus application is deployed as
deployment and cStor volume is configured to have
3 replicas. Node reboots may be common during Kubernetes upgrade. Maintain volume replica quorum in such instances. See here for more details.
Sample YAML specs
Sample cStor Pool spec
apiVersion: openebs.io/v1alpha1 kind: StoragePoolClaim metadata: name: cstor-disk spec: name: cstor-disk type: disk maxPools: 3 poolSpec: poolType: striped disks: diskList: - disk-3326ca3a735ba9cbe5a7753d12d5a55a - disk-d80800ca121b85b136d6a50a1079c921 - disk-49e1ca76d1901a01ff6f366b8c53e44a
apiVersion: storage.k8s.io/v1 kind: StorageClass metadata: name: openebs-cstor-disk annotations: openebs.io/cas-type: cstor cas.openebs.io/config: | - name: StoragePoolClaim value: "cstor-disk" - name: ReplicaCount value: "3" # value: |- # memory: 1Gi # cpu: 200m #- name: AuxResourceLimits # value: |- # memory: 0.5Gi # cpu: 50m #(Optional) Below 3 lines schedules the target pods deployed on the labeled nodes #- name: TargetNodeSelector # value: |- # node: appnode provisioner: openebs.io/provisioner-iscsi
PVC spec for Prometheus
kind: PersistentVolumeClaim apiVersion: v1 metadata: name: cstor-prometheus-storage-volume-claim namespace: openebs spec: storageClassName: OpenEBS-cStor-Prometheus accessModes: - ReadWriteOnce resources: requests: storage: 500G
PVC spec for Grafana
kind: PersistentVolumeClaim apiVersion: v1 metadata: name: grafana-cstor-claim namespace: grafana-cstor spec: storageClassName: OpenEBS-cStor-Prometheus accessModes: - ReadWriteOnce resources: requests: storage: 50G
See the sample spec files for Grafana using cStor here.