Etcd in the control plane of Kubernetes clusters which are managed by Gardener is deployed as a StatefulSet. The statefulset has replica of a pod containing two containers namely, etcd and backup-restore. The etcd container calls components in etcd-backup-restore via REST api to perform data validation before etcd is started. If this validation fails etcd data is restored from the latest snapshot stored in the cloud-provider's object store. Once etcd has started, the etcd-backup-restore periodically creates full and delta snapshots. It also performs defragmentation of etcd data periodically.
The etcd-backup-restore needs as input the cloud-provider information comprising of security credentials to access the object store, the object store bucket name and prefix for the directory used to store snapshots. Currently, for operations like migration and validation, the bash script has to be updated to initiate the operation.
- Deploy etcd and etcd-backup-restore using an etcd CRD.
- Support more than one etcd replica.
- Perform scheduled snapshots.
- Support operations such as restores, defragmentation and scaling with zero-downtime.
- Handle cloud-provider specific operation logic.
- Trigger a full backup on request before volume deletion.
- Offline compaction of full and delta snapshots stored in object store.
The existing method of deploying etcd and backup-sidecar as a StatefulSet alleviates the pain of ensuring the pods are live and ready after node crashes. However, deploying etcd as a Statefulset introduces a plethora of challenges. The etcd controller should be smart enough to handle etcd statefulsets taking into account limitations imposed by statefulsets. The controller shall update the status regarding how to target the K8s objects it has created. This field in the status can be leveraged by HVPA to scale etcd resources eventually.
The etcd CRD should contain the information required to create the etcd and backup-restore sidecar in a pod/statefulset.
apiVersion: druid.gardener.cloud/v1alpha1
kind: Etcd
metadata:
finalizers:
- druid.gardener.cloud/etcd
name: test
namespace: demo
spec:
annotations:
app: etcd-statefulset
gardener.cloud/role: controlplane
networking.gardener.cloud/to-dns: allowed
networking.gardener.cloud/to-private-networks: allowed
networking.gardener.cloud/to-public-networks: allowed
role: test
backup:
deltaSnapshotMemoryLimit: 1Gi
deltaSnapshotPeriod: 300s
fullSnapshotSchedule: 0 */24 * * *
garbageCollectionPeriod: 43200s
garbageCollectionPolicy: Exponential
imageRepository: eu.gcr.io/gardener-project/gardener/etcdbrctl
imageVersion: v0.25.0
port: 8080
resources:
limits:
cpu: 500m
memory: 2Gi
requests:
cpu: 23m
memory: 128Mi
snapstoreTempDir: /var/etcd/data/temp
etcd:
Quota: 8Gi
clientPort: 2379
defragmentationSchedule: 0 */24 * * *
enableTLS: false
imageRepository: eu.gcr.io/gardener-project/gardener/etcd-wrapper
imageVersion: v0.1.0
initialClusterState: new
initialClusterToken: new
metrics: basic
pullPolicy: IfNotPresent
resources:
limits:
cpu: 2500m
memory: 4Gi
requests:
cpu: 500m
memory: 1000Mi
serverPort: 2380
storageCapacity: 80Gi
storageClass: gardener.cloud-fast
sharedConfig:
autoCompactionMode: periodic
autoCompactionRetention: 30m
labels:
app: etcd-statefulset
gardener.cloud/role: controlplane
networking.gardener.cloud/to-dns: allowed
networking.gardener.cloud/to-private-networks: allowed
networking.gardener.cloud/to-public-networks: allowed
role: test
pvcRetentionPolicy: DeleteAll
replicas: 1
storageCapacity: 80Gi
storageClass: gardener.cloud-fast
store:
storageContainer: test
storageProvider: S3
storePrefix: etcd-test
storeSecret: etcd-backup
tlsClientSecret: etcd-client-tls
tlsServerSecret: etcd-server-tls
status:
etcd:
apiVersion: apps/v1
kind: StatefulSet
name: etcd-testAs first step implement defragmentation during maintenance windows. Subsequently, we will add zero-downtime upgrades and defragmentation.
