Commandeering Kubernetes with Elixir

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Cory O’Daniel (apostrophe not required) Senior YAML Architect @ Container Heroes Creator of Bonny Kubernetes Development Framework @coryodaniel @coryodaniel

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Why do we extend? The operator pattern allows you to codify the expertise of a human operator with deep knowledge of managing an application or set of services and how to react if there are problems.

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Why do we extend? Declarative Highly Available Databases

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Why do we extend?

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Why do we extend? On-demand database snapshots

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Why do we extend?

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Why do we extend? Generating TLS Certificates

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Why do we extend?

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Why do we extend? Creating S3 Buckets

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Why do we extend?

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The Operator pattern for extending Kubernetes ● Process a chunked HTTP stream of add, modify, and delete events ● Continually reconcile k8s resources’ state changes ● Manage background tasks, processes, and state

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Why Kubernetes? Service Discovery and Load Balancing NODE NODE Where is microservice-a.prod.svc.cluster.local NODE MASTERS

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Why Kubernetes? Scaling NODE NODE NODE NODE

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Why Kubernetes? Storage Orchestration NODE NODE NODE SSD NFS Host Path

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Why Kubernetes? Automated rollouts / rollbacks v1 NODE v1 NODE v1 NODE v2 v2 v2

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Why Kubernetes? Automated bin packing

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Why Kubernetes? Self-healing NODE NODE NODE

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Why Kubernetes? ● Secret and Config Management ● Single deployment tool/interface ● Portability

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Kubernetes Crash Course

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Resource Attributes And Metadata

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Metadata as REST Path

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`kubectl explain pod` ● 1 or more colocated docker containers ● Acts as a “logical host” ● Share volumes ● Share network ● Live and die as a unit

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`kubectl explain deployment` ● Declarative management of pods ○ Desired number of pod replicas ○ Rollout Strategy ○ Revision History

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`kubectl explain service` ● Exposes a set of pods as a network service ● Selects pods using labels

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Life of a Deployment

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Scheduler ETCD Master Components NODES Deployment ReplicaSet Pod API Server Deployment Controller ReplicaSet Controller Ctrl Manager HTTP POST HTTP GET deployment/nginx replicaset/nginx-jk1234 pod/nginx-jk1234-6963

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Node Components MASTERS kubelet docker TCP 8888 TCP 4269

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Writing a Kubernetes Operator

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Our first operator: Todos App Create a Custom Resource Definition (CRD) ● Generates a REST Endpoint ● Defines the fields and validations we expect

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Our first operator: Todos App Create a Controller ● Polls REST endpoint ● Reconciles changes in resource state

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Todo CRD: YAML Warning

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Todo Resource

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Interacting with your Custom Resource

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Creating a Controller

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Building and Deploying an Operator

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Creating and Deleting Todos

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Where do we go from here?

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Applications are long running, side-effect filled functions with env vars, flags, and config files as arguments.