Kubernetes operators
根据Rob Szumski的presentation
Kubernetes operator是把专家平常的经验，流程，比如写在wiki里面的诀窍，使用Operator来固化。这些经验就会集成在Operator软件里面。
换句话说，这个叫做Best practices. 也是软件工程里面把logic封装起来的一个例子。It’s a fancy script.
比如failover，用软件来建立模型。使用K8S的原语，比如stateless workload，stateful workload，服务发现等来实现。
好处是到处可以使用，跨平台。
Kubernetes提供了一个Operator框架，供大家使用。控制集群里面的节点。
- Operator SDK for Build
- Operator Lifecycle manager for Run, 多个Operator的生命周期，比如版本。
- Operator Metering for Operate，收集统计信息。
业界Open operators, 提供在github。比如etcd，Spark， MongoDB.
例如，mongoDB提供了operator，封装了创造ReplicaSet的best practice。在PROD namespace，用户提供High level configuration，提供Intention about如何部署。Operator会帮助deploy。
另外一个例子，根据Luke Bond的video, Cassandra需要把3节点扩展到5节点的时候，因为是stateful应用，需要做一系列的动作，这个知识就可以封装在operator。就像Kubectl增加instance的数量一样。
etcd的operators
- create/destroy
- resize
- backup
- upgrade
BTW，CoreOS还提供Prometheus，rook的operators。
Operator model
- Observe：2 running pods, different version (one is old)
- Analyze: should run 3 pods and in the latest version
- Act: Recover 1 member, backup cluster, upgrade one pod to the latest version.
- //create an operator
kubectrl create -f xxxx.yaml
run the operator… Launch an operator container
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create a new third party type when installed into K8s.
The code is using k8s libraries. For example, in Go, you can import k8s libs. -
Using k8s primitives like Services and Replica Sets. For example, Etcd operator uses a ReplicaSet with replica=1
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Operators should be backward compatible and understand previous versions of resources.
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Should be online change without affecting databases running.
chaos monkey can be a special operator that wakes up periodically and kills stuff, for example, a pod using k8s APIs.