Kinds of Controllers

ReplicaSets

• Specified number of replica pods are running at all times

• Else will start a new pod when it crashes

• Used within deployment

Deployments

• Declarative updates for pods and ReplicaSets

• Describe desired state of deployment in yaml file and deployment controller aligns actual state to match

• Create/replace replicaSets

• Deployments manages ReplicaSets which manages Pods (quick and flexible rollback)

• Use Cases

  • Pod Management

  • Scaling a ReplicaSet

  • Pod Updates/Rollbacks

  • Pause (only updates are paused not traffic) /Resume deployments (larger change sets)

  • Status - pod health issues

Daemon Sets

• Ensures all nodes run a copy of the specific pod

• Add/remove pods according to add/remove nodes in cluster

• Deleting this deletes all pods it created

• Use Case

  • Log aggregator

  • Monitoring agent on node

Jobs

• Supervisor for pods carrying out batch jobs

• Cron job - specific job at specific time

• Eg. nightly report, database backups etc.

Services

• Allows communication btw sets of deployment with another

• Unique IP (unchanging)

• Pods configured to rely on service IP

• Allows 2 deployments (set of pods) to talk

• Types:

  • Internal: IP reach within cluster

  • External: EP available through Node IP: port (NodePort)

  • Load balancer: K8s in cloud