Kubernetes

https://www.youtube.com/watch?v=H-FKBoWTVws https://github.com/reactiveops/k8s-workshop/tree/master/complete https://console.cloud.google.com/getting-started?_ga=2.201732755.-327865664.1531857474&pli=1&tutorial=gke_quickstart Pluarlsight: Getting Started with Kubernetes

Kubernetes is a tool that orchestrates microservices that are build into containers

Kubernetes is a tool that helps:

• Ensure your apps are up 24/7 (as close as possible)
• Devs can deploy code multiple times per day
• Use cloud resources effeciently
• Fault-tolerant, self-healing
• Scalability

K8s Building Blocks

Cluster

* made of of masters and nodes

Masters

parts of the master: * kube-apiserver * exposes the REST API * consumes JSON through mainfest files * cluster store * uses etcd (a key value store) * stores state and config * ensures the data is distributed, observable and consistent * kube-controller-manager * controles nodes, enpoints and namespace controllers * watches for changes * maintains desired state * kube-scheduler * watches the apiserver for changes

Nodes

parts of the node: * kubelet * main k8s agent * register node with cluster * watches apiserver * creates pods * reports to master * endpoint is exposed on :10255 * controller * pulls images * starts and stops containers * usually docker * kube-proxy * handles networking * pod IP addresses * all containers in a pod have the same IP * load balances across a service

Pods

* The 'atom' of K8s
* Deploying a pod is all or nothing: either it works or it doesn't
* Made up of one or more containers
* Defined in a manifest file
* The manifest file is sent to the apiserver
* The scheduler deploys it to a node 
* No matter how many containers are in your pod, they share an IP 

Services

* Pods (and their IPs) are frequently killed; there is a lot of IP churn
* A reliable network endpoint
* Sits in front of a set of pods 
* Has a stable IP, DNS and Port so that if a pod is killed and new one if spun up, the contents are always available 
* A service load balances and decides which pods recieve requests 
* Labels allow you to connect pods to services 
* You can configure a service to point to things outside of a cluster
* You can find services in 2 ways:
    1. environment variables
    2. DNS
There are 3 types of Services in Kubernetes 
1. NodePort 
    * exposes the cluster to the 'outside' through a TCP or UDP port 
2. LoadBalancer
    * Only sends traffice to healthy pods 
3. ClusterIP (default)
    * creates a stable, internal IP

Deployments

* Deployments and rollbacks! 
* Provides declarative updates for pods and replicasets 

Labels

Replica Set vs. Replica Controller

Question: How are databases run in K8s?