6.2 Kubernetes: the core objects
You can read a Kubernetes manifest and predict what the cluster will do with it.
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- On AWS
- EKS
- On Azure
- AKS
- On Google Cloud
- GKE
Kubernetes is a reconciliation loop: you declare the state you want, and the cluster works continuously to make reality match. This topic covers the core objects that declaration is written in — pods, ReplicaSets, Deployments, Services, Ingress, ConfigMaps, Secrets — and the namespaces and resource limits that keep tenants apart. It sits at the centre of the module because reading a manifest and predicting the cluster's behaviour is the fundamental skill. The confusion to clear early is that pods are not machines and not durable; everything above them exists because they are expected to die.
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Pods, ReplicaSets, Deployments and the reconciliation loop
A pod is the smallest deployable unit, a replica set keeps a count of them running, and a deployment manages changes to that set. Underneath all of it, a loop is continuously comparing what you asked for against what exists.
Services, Ingress and how traffic reaches a pod
Traffic reaches a pod through a stable internal address and, from outside, through an ingress that routes by host and path. Pods come and go, which is exactly why the addressing works this way.
ConfigMaps, Secrets and mounting configuration
Configuration and credentials are supplied separately from the image, so one image can run in every environment. Keeping them out of the image is the practice that makes promotion between environments possible.
Namespaces, requests/limits and resource pressure
Namespaces divide a cluster, and the requests and limits you declare are how the scheduler decides what fits where. Declaring them badly is the most common cause of a cluster that behaves unpredictably under load.
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