Kubernetes

What is the master node?

It provides a running environment for the control plane responsible for managing the state of Kubernetes cluster, and it is the brain behind all operation inside the cluster.

Control Plane

Manages the nodes and the Pods in the cluster.

ExternalName

Maps the service to the contents of the externalName field (e.g. foo.bar.d1iq.com), by returning the CNAME record with its value. No proxying of any kind is set up.

How does Kubernetes ensure the control plane's fault tolerance?

Master node replicas are added to the cluster, configured in High-Availability (HA) mode.

Why use container orchestrators?

Most container orchestrators can: - Group hosts together while creating a cluster. - Schedule containers to run on hosts in the cluster based on resources availability. - Enable containers in a cluster to communicate with each other regardless of the host they are deployed to in the cluster. - Bind containers and storage resources. - Group sets of similar container and bind them to load-balancing constructs to simplify access to containerized applications by creating a level of abstraction between the containers and the user. - Manage and optimize resource usage - Allow for implementation of policies to secure access to applications running inside containers.

What are the basic pod attributes?

Name, image, ports, env, command, args

Where is a ClusterIP located?

Only on the cluster

What are some monitoring solutions for Kubernetes?

Prometheus, Elastic Stack, DATADOG and dynatrace

What are the two deployment strategies?

Recreate and Rolling update

What does a service do?

Redirects traffic from a specific IP, NodePort, LoadBalancer, etc, to the appropriate pod(s) based on the deployment.

Container Runtime Engine

Responsible for running the client workloads in their appropriate containers.

What is the default deployment strategy?

Rolling update

What field will tell you to deployment strategy that was used on a pod?

The StrategyType field in the pod definition

What reconciles differences between the things that you want Kubernetes to do and things that you have?

The manage-controller.

What is the role of the Scheduler?

The role of the kube-scheduler is to assign new objects, such as pods, to nodes.

What are Nodes?

The working machines in your cluster. Referring to broadly as either Nodes or Worker Nodes.

What are Kubernetes addons?

They are cluster features and functionality not yet available in Kubernetes, therefore implemented through 3rd-party pods and services.

What are microservices?

They are lightweight applications written in various modern programming languages, with specific dependencies, libraries and environmental requirements.

What are components of the master node?

- API Server - Scheduler - Controlled managers - ectd

What are pods?

- Atomic unit or smallest "unit of work" of Kubernetes. - Foundational building blocks of Kubernates workloads. - Pods are one or more container that share volumes and a network namespace.

What are the components of a worker node?

- Container runtime - kubelet - kube-proxy - Addons for DNS, Dashboard, cluster-level monitoring and logging.

What are some Kubernetes features?

- Automatic bin packing - Self-healing - Horizontal scaling - Service discovery and Load balancing - Automated rollouts and rollbacks - Secret and configuration management - Storage orchestration - Batch execution

What are some examples of Kubernetes addons?

- DNS - cluster DNS is a DNS server required to assign DNS records to Kubernetes objects and resources - Dashboard - a general purposed web-based user interface for cluster management - Monitoring - collects cluster-level container metrics and saves them to a central datastore - Logging - collects cluster-level container logs and saves them to a central log store for analysis.

What is the kube-proxy?

- Has appropriate plugins for the chosen container networking interface (CNI). - Takes care of DNS & discovery services. - Allows communication among pods and to the outside world.

Kubernetes does three things.

- Keeps a list of things you want. - Keeps a list of things you have. - Will consolidate between both things.

Application Container

- Might take more resources that we'd like. - Could have odd or cryptic bugs. - No way of knowing if it's cutting edge or legacy code that has to be containerized.

What are the main components of the Kubernetes architecture?

- One or more master nodes - One or more worker nodes - Distributed key-value store, such as etcd

What are examples of CRI shims?

- dockershim - cri-containerd - CRI-O

What is a monolith?

A large, single piece of software which continuously grows, it has to run on a single system which has to satisfy its compute, memory, storage, and networking requirements.

What kind of algorithm does a service use to loadbalance?

A random algorithm

What is a Network Policy?

A specification of how groups of pods are allowed to communicate with each other and other network endpoints.

Container Network Interface (CNI)

An open-source project that is focused on establishing a standard specification for integrating container with network providers.

What is a container?

Application-centric methods to deliver high-performing, scalable application on any infrastructure of you choice.

Can pods communicate with each other?

By default all pods can communicate with each other in the same cluster without restriction

LoadBalancer

Exposes the service externally using a cloud provider's load balancer.

NodePort

Exposes the service on each Node's IP at a static port (the NodePort).

LoadBalancers services

Extends NodePort and works in conjunction with and external system to map a cluster external IP to the exposed service

A scheduler's job is quite simple in multi-node Kubernetes clusters.

False. It is extremely important and quite complex.

etcd is written in Python programming language.

False. It is written in Go programming language.

Pods can not communicate with each, even in the same cluster.

False. Pods are expected to be able to communicate with all other Pods in the cluster, all this without the implementation of Network Address Translation (NAT).

Taints are set on Pods

False. Taints are set on Nodes.

Job/CronJob Pods are meant to be long running.

False. The are meant to run, complete a task and exit with a status code.

All administrative tasks are coordinated by the scheduler.

False. There are coordinated by the API server, kube-apiserver, a central control plan component running on the master node.

Controlled managers are distributed key-value data store used to persist a Kubernetes cluster's state.

False. They are control plan components on the master node running controllers to regulate the state of the Kubernetes cluster.

What language is etcd written in?

Go

Who designed Kubernetes?

Google but is now managed by Cloud Native Computing Foundation.

What was the original program that enabled monitoring and the analysis feature for Kubernetes?

Heapster, although it is now deprecated and a slimmed down version was created called Metrics Server.

CRI implements what two services:

ImageService and RuntimeService

What is a container image?

It bundles the application along with its runtime and dependancies, and a container is deployed from the container image offering an isolated executable environment for the application.

What is the kubelet?

It is an agent running on reach node and communicates with the control plane components from the master node.

What is Kubernetes?

It is an open-source container-orchestration system for automating application deployment, scaling and management.

Where is the cluster configuration saved?

It is save to etcd

Where is the Kubernetes cluster state and all cluster configuration data saved to?

It is saved to etcd. However, etcd is a distributed key-value store which only holds cluster state related data, no client workload data.

What is a container orchestrator?

They are tools which group systems together to form clusters where containers' deployment and management is automated at scale while meeting the requirements which are: - Fault-tolerance - On-demand-scalability - Optimal resource usage - Auto-discovery to automatically discover and communicate with each other - Accessibility from the outside world - Seamless updates/rollback without any downtime

What does a worker node do?

They provide a running environment for client applications.

What does the kubelet connect to?

To the container runtime using Container Runtime Interface (CRI).

A scheduler's job in a single-node Kubernetes clusters is quite simple.

True.

API server is the only master plane component that can talk to etcd data store.

True.

One pod runs on one node always.

True.

Regardless of the how many containers a pod may have it will always run on one node.

True.

Taints are set on Nodes.

True.

Taints do not attract work they only repel work.

True.

The API server intercepts RESTful calls from users, operates and external agents, then validates and processes them.

True.

The InitContainer runs once per Pod.

True.

The kubelet connects to the container runtime using Container Runtime Interface (CRI).

True.

Tolerants are set on Pods

True.

You can run multiple containers in a single pod.

True.

etcd is a distributed key-value data store used to persist a Kubernetes cluster's state.

True.

Is it important to keep the control plan running at all costs?

Yes, losing the control plan may introduce downtimes, causing service disruption to clients, with possible loss of business.

What is a sample service:

apiVersion: v1 kind: Service metadata: name: my-service spec: selector: app: MyApp ports: - 80

Metrics Server stores data

in-memory so you can view historical performance data.

What is the command to get all of the pods running on your cluster?

kubectl get pods

CRI consists of:

protocol buffers, gRPC API, and libraries