What is an Operator?
- Docker & Kubernetes course
- Expert
- Lesson 13/47
- 4 min
Learn that the Operator pattern encodes human knowledge.
What is an operator?
An operator is a Kubernetes controller that turns the knowledge of operating an application (installation, backup, upgrade, failover) into code. It usually comes with a CRD: the user writes a high-level request ("3-replica PostgreSQL, a backup every night"), and the operator creates and manages the needed StatefulSets, Services, Secrets and CronJobs.
apiVersion: postgresql.cnpg.io/v1
kind: Cluster
metadata:
name: magaza-db
spec:
instances: 3
storage:
size: 20Gi
# the CloudNativePG operator manages the pods, replication and failoverCommon operators: CloudNativePG, Strimzi (Kafka), Prometheus Operator, cert-manager, ECK (Elasticsearch).
Installing an operator
Operators are usually installed with Helm or a single manifest; the installation brings the CRDs, the operator Deployment and the RBAC permissions. After installing, you work with the types the operator introduces:
kubectl apply --server-side -f https://raw.githubusercontent.com/cloudnative-pg/cloudnative-pg/release-1.24/releases/cnpg-1.24.1.yaml
kubectl get crds | grep cnpg
kubectl get deploy -n cnpg-systemPractice A database with an operator
Write a Cluster YAML for CloudNativePG: apiVersion: postgresql.cnpg.io/v1; name magaza-db, namespace magaza; spec.instances: 3; spec.storage.size: 20Gi.
Starter code
# buraya yazSample solution
apiVersion: postgresql.cnpg.io/v1
kind: Cluster
metadata:
name: magaza-db
namespace: magaza
spec:
instances: 3
storage:
size: 20GiExpected output
cluster.postgresql.cnpg.io/magaza-db created $ kubectl get cluster -n magaza NAME AGE INSTANCES READY STATUS PRIMARY magaza-db 2m 3 3 Cluster in healthy state magaza-db-1
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What is the main difference between an operator and a Helm chart?
- An operator keeps running after installation and manages the app; Helm only installs/upgrades Correct answer
- Helm is more powerful
- An operator doesn't use YAML
- There's no difference
Explanation: Jobs like failover need continuous observation and reaction.
2 Specify the number of PostgreSQL instances the operator manages.
kind: Cluster
spec:
____: 3kind: Cluster
spec:
instances: 3Explanation: In CloudNativePG, the replica count is instances.
3 Match the operators.
| Term | Meaning |
|---|---|
CloudNativePG |
PostgreSQL |
Strimzi |
Kafka |
cert-manager |
Certificates |
ECK |
Elasticsearch |