Kubernetes introduction and architecture¶
- Kubernetes is container orchestrator making many servers act like one.
- Kubernetes usually run's on top of
dockerbut can use other container runtimes like
- Kubernetes provides API/CLI to manage containers across servers
- Similar to linux distributions there are kubernetes distributions as well
Advantages of Docker Swarm¶
- Comes with docker, single vendor container platform
- Easiest to deploy & manage
- Can run anywhere docker does Eg: local, cloud, datacenter, ARM, windows 32-bit, 64-bit
- Secure by default (mutual tls authentication in swarm, encrypted control plane & database secrets)
- Easier to troubleshoot
Advantages of Kubernetes¶
- Cloud/Infrastructure vendors will deploy/manage kubernetes
- Wide adoption in the community
- Flexible: cover a wide range of use cases
Cluster - A deployment of kubernetes. It provides management, orchestration, healing & service access.
Node - Resources; Compute to run pods which are placed inside nodes
Pod - One or more containers; Smallest unit in kubernetes; often 1 container runs in 1 pod.
- Kubernetes does not run containers directly, it runs pods (Containers encapsulated in pods)
- Pod is the smallest unit of deployment in kubernetes
- Pod is a single instance of an application
- A single pod can have multiple containers but they are usually not multiple containers of the same application Eg:
Helper container. However, this is a rare use case
- Containers in a pod share the same IP address and port space (Can communicate with each other using localhost)
Job - Ad-Hoc task. One or more pods are created for the job until completion.
Ingress - Exposes a external component to the service
Ingress Controller - Used to provide ingress (Eg: AWS LB Ingress Controller uses ALB/NLB)
Persistent Storage/Persistent Volumes - Volume whose lifecycle lives beyond any 1 pod using it.
- Components in the Kubernetes system that monitor and manage the state of the resources running in a Kubernetes cluster.
Types of controllers¶
- Run multiple instances of a pod across the cluster providing fault tolerance and high availability
- Even in a single node cluster, replication controller can be used to restart a pod if it fails
Replication controller is deprecated in favor of ReplicaSet
- ReplicaSet is a controller that manages a set of pods
- ReplicaSet ensures that a specified number of pod replicas are running at any given time
- ReplicaSet is the next generation Replication Controller
- ReplicaSet is the recommended way to manage pods