Table of Contents
Learning - Kubernetes Operator
Used for Stateful Applications on K8s
Stateless Applications on K8s
Control loop
Observe => Check Differences => Take Action => Observe ...
- Recreate died pods
- restart updated pods
Stateful Applications WITHOUT Operator
Data Persistence
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more "hand-holding" needed
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throughout whole lifecycle
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all 3 replicas are different
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own state and identity
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order important
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Process different for each application
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So, no standard solution
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manual intervention necessary
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people, who "operate" these applications
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can not archive automation, self-healing
Stateful application WITH Operator
To manage stateful application
Replaces human operator with software operator.
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How to deploy the app?
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How to create cluster of replicas?
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How to recover?
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tasks are automated and reusable
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One 1 standard automated process
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more complex/more environments => more benefits
Control loop mechanism
watch for changes
Observe => Check Differences => Take Action => Observe ...
It is custom control loop
make use of CRD’s
Custom Resource Definitions
- custom K8s component (extends K8s API)
Your own custom component
domain/app-specific knowledge
CRD's, StatefulSet, ConfigMap, Service, ...
automates entire lifecycle of the app it operates
Summary
- Managing complete lifecycle of stateless apps
No business logic necessary to: create, update, delete - K8s can't automate the process natively for stateful apps
Operators: prometheus-operator, mysql-operator, postgres-operator, elastic-operator
For example: MySQL
- How to create the mysql cluster
- How to run it
- How to synchronize the data
- How to update
OperatorHub.io
Operator SDK to create own operator