68 lines
2.5 KiB
Markdown
68 lines
2.5 KiB
Markdown
---
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title: Intro Basis Components of K8s
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updated: 2022-02-05 15:10:02Z
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created: 2022-01-29 15:33:56Z
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latitude: 52.38660000
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longitude: 5.27820000
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altitude: 0.0000
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---
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What is Kubernetes (K8s)
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- container orchestration tool
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- manages containers (not only Docker)
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- different environments
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- physical
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- virtual
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- cloud
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What problems solves Kubernetes:
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- manages many containers with independent services, like micro services
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Kubernetes features
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- High Availability (no downtime)
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- Scalability (high performance)
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- Disaster recovery (backup and restore)
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Kubernetes components (but many more)
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- Node (physical or virtual)
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- node contains pods and per pod usually 1 application
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- pod is smallest unit of K8s
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- pod is abstraction over container
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- each pod gets its own ip-address
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- new ip-address on re-creation
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- 
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- Services
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- permanent ip-address
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- lifecycle of Pod and Service are not connected
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- 
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- External Service
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- opens the communication for external sources
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- internal service for eq database. Not accessible from outside
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- External request go first to Ingress (to route traffic)
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- 
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- ConfigMap & Secret
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- external configuration of application (eq URL of a database DB_URL = mongo-db-service)
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- secret credentials in Secret (like configMap but base64 encoded)
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- Application can read from ConfigMap and Secret
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- Volumes
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- for persistent data
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- attach physical storage to a pod
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- local machine or remote storage (eq cloud and outside k8s cluster)
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- k8s does not manage data persistence
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- Deployment and Stateful Set
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- Every Pod is replicated as specified in BluePrint
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- Service has 2 functionalities:
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- Permanent IP (so an other pod can connect of the pod dies)
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- load balancer
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- the pod is not created, but for every pod is specified (Blueprint) how many replicas are required
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- Blueprint is abstraction of Pods. Pods are an abstraction of Containers
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- In practice just working with Deployments
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- Stateful Set
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- Databases have state and can not be replicated
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- For stateful applications like databases
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- no database inconsistency can occur.
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- is not easy therefor advice to host databases outside K8s cluster |