Kubernetes overview

Kubernetes Hierarchy

  • image
  • container
  • pod ( one or more containers that would be deployed together on the same host to share volumes )
  • deployment
  • service

Kubelet

Kubelets run on every host to start and stop pods and communicate with the Docker engine on the host level.

Kube-proxy

Kube-proxies also run on every host to redirect the traffic to specific services and pods.

Container Linux

Container Linux by CoreOS (formerly known as CoreOS Linux, or just CoreOS) an OS specifically designed to run containers, a lightweight Linux distribution that uses containers to run applications. It does not even have a package manager, but contains the basic GNU Core Utilities for administration. It also include include Kubelet, Docker, etcd and flannel.

Kubernetes Networking

Flannel

Flannel gives each host a separate IP subnet range to prevent IP address collisions, providing a unique IP address to each container. Flannel is the standard SDN ( software-defined network ) tool for CoreOS (Container Linux), it is shipped with the distribution.

Calico

Calico provides security in the Kubernetes cluster. By default in the Kubernetes cluster any pod can communicate to any other pod on any host. Calico restricts the inter pod communication using namespaces and selectors. It allows the communication from the host to the pods to enable health checks. Calico has tight integration with Flannel.

Canal

As Calico and Flannel nicely fit together, Canal is the combination of the two to provide a comprehensive inter-pod networking solution in the Kubernetes cluster.

Kubernetes commands

  • kubectl get – list resources
  • kubectl describe – show detailed information about a resource
  • kubectl logs – print the logs from a container in a pod
  • kubectl exec – execute a command on a container in a pod

List existing pods

kubectl get pods

Get detailed information on the pods

kubectl describe pods

Start a proxy to access the containers within the pod

kubectl proxy

Get the pod name and store it in the POD_NAME environment variable

export POD_NAME=$(kubectl get pods -o go-template --template '{{range .items}}{{.metadata.name}}{{"\n"}}{{end}}')
echo Name of the Pod: $POD_NAME

Access an API running in the pod. The name of the pod is in the POD_NAME environment variable

curl http://localhost:8001/api/v1/namespaces/default/pods/POD_NAME/proxy/

View the STDOUT of the only container of the pod

kubectl logs POD_NAME

View the STDOUT of a specific container of the pod

kubectl logs POD_NAME -c CONTAINER_NAME

View the STDOUT of all containers of the pod

kubectl logs POD_NAME --all-containers=true

Execute a command in the only container of the pod

kubectl exec POD_NAME MY_COMMAND

Execute a command in a container of the pod

kubectl exec POD_NAME -c CONTAINER_NAME MY_COMMAND

Start a Bash session in the container (container name is optional if the pod has only one container)

kubectl exec -ti POD_NAME -c CONTAINER_NAME bash

To check an API from the Bash console within the container (use localhost to address it within the container)

curl localhost:8080

Force the deletion of all pods of a deployment

Make sure the MY_DEPLOYMENT_NAME only returns the pods you really want to delete

# IMPORTANT!!!
# First make sure the query only returns the list of pods you really want to delete

kubectl get pods | grep MY_DEPLOYMENT_NAME | awk '{print $1}')

Execute the command to delete the pods

while IFS= read -r result
do
    kubectl delete pod $result --grace-period=0 --force
done < <(kubectl get pods | grep MY_DEPLOYMENT_NAME | awk '{print $1}')

Install missing commands on Linux distributions

On some lean systems, mostly in Docker containers, some important commands are not readily available. The table below shows the command to install them.

To get the name of the Linux distribution execute

cat /etc/os-release

To find the package that contains the command, install apt-file

sudo apt-get install apt-file

Update the file package mapping database

sudo apt-file update

Search for the command at the end of the path

apt-file search --regexp '/MY_COMMAND$'

Select the package that contains the command in the standard path (/usr/bin/)

To get more information on the package

apt-cache show MY_PACKAGE

Application install commands

ApplicationRHEL, CentOSUbuntu, Debian
free, kill, pkill,
pgrep, pmap,
ps, pwdx, skill,
slabtop, snice,
sysctl, tload,
top, uptime,
vmstat, w, watch		apt-get install procps
telnetyum install telnet -yapt-get install telnet

The advancement of computer programming and personal computer technology

If you really know one programming language, you can learn others too. The most important part is to understand the concept of computer programming. All languages are built on similar type of instructions, some of them require a semicolon at the end of the line, others don’t. Some of them use curly braces {} to group instructions, others use indentation.

All of them allow you to make decisions, usually with the keyword IF, assign values to variables with =, read the keyboard, write to the screen, read and write the disk, and the network. Loop through items with FOR, FOREACH, and WHILE, address array elements with [0..]. You only have to learn a few English words and the syntax to use them.

The internet, and especially Stack Overflow is a great resource to find sample code that does what you need. Avoid assembling your program by copy pasting code from the internet. Try to understand the examples, and write your own lines to be able to really understand and maintain it.

The list below shows the advancement of personal computer technology. I have added the usual hardware specifications, the most popular operating systems, and important programming languages. The dates are not when the technology was announced, but when the average user started to use it.

1981

IBM Mainframe, magnetic tape and large format magnetic disk storage

  • Fortran

Homemade personal computer with no permanent storage

  • Basic

“Midrange” computer (16 KB solid state or magnetic-core RAM, large format magnetic disk storage )

  • Basic

1984

ZX 81 (3.25 MHz processor, first 1 KB, later 16 KB RAM, compact audio cassette storage)

ZX Spectrum (3.5 MHz processor, 16 KB RAM, compact audio cassette storage)

Commodore 64 (1 MHz processor, 64 KB RAM, 5.4″ floppy disk)

  • Basic for data processing
  • Simon Basic for graphical user interface

IBM PC( 4.7 MHz processor, first 128 KB, later 256 KB RAM, 5.4″ floppy disk, later 10 or 20 MB 5.4″ hard drive)

DOS

  • dBase
  • Clipper
  • FoxPro

1987

IBM XT ( 4.7-12 MHz processor, 16 MB RAM)

DOS

  • Lotus 123 spreadsheet for engineering calculations
  • LISP for AutoCAD menus

1994

IBM 386 ( 40 MHz processor, 256 MB RAM)

DOS, Windows 3.1

  • FoxPro
  • Visual FoxPro
  • Visual Basic
  • SQL

1998

IBM clone( 40 MHz processor, 256 MB RAM)

Windows 95

  • PowerBuilder
  • Jaguar for web application server
  • ASP for web UI
  • SQL databases

2000

IBM clone ( 150 MHz processor, 512 MB RAM)

Windows 98, Windows ME, Windows 2000

  • ASP for web UI
  • Visual Basic
  • SQL databases

Linux Debian

  • Bash

2003

( 1 GHz processor, first 1 GB, later 4 GB RAM)

Windows Server 2003

  • C#
  • C++
  • Java
  • SQL databases

2008

( 1 GHz processor, first 4 G, later 32 GB RAM)

Windows Server 2008

2015

Windows 7 laptop (2 GHz processor, 6 GB RAM, 500 GB HD)

Windows Server 2012 R2 virtual machines in the cloud ( 2 GHz processor, 4 – 32 GB RAM)

  • PowerShell

Linux RedHat 7 ( virtual machines in the cloud 2 GHz processor, 4 – 32 GB RAM)

  • Bash

MacBook Pro laptop (2.5 GHz i7 processor, 16 GB RAM, 1TB SSD storage)

  • Packer
  • Terraform
  • Ruby
  • PowerShell ( on Windows 10 virtual machine )
  • Chef
  • ServerSpec
  • InSpec
  • Chocolatey

2019

MacBook Pro (5 GHz i9 processor, 32 GB RAM, 1TB SSD storage)

  • Docker
  • Kubernetes
  • Golang

Install Windows from a USB drive

Modern computers don’t have DVD drives anymore. To install Windows on a new system you need to place the Windows installation media on a bootable USB drive. To prepare the bootable USB drive you need a working computer with Windows.

Create the bootable USB media

Install Windows

  • Restart the computer and enter into the BIOS settings
    • On Toshiba laptops press the F2 key while the Toshiba logo is shown
  • Set the USB drive as the first item in the boot order and save the new BIOS settings
  • When the computer boots from the USB drive follow the instructions to install the Operating system
  • When the computer automatically reboots during the OS installation, remove the USB drive to let the machine boot from the hard drive and complete the Windows configuration.

Microsoft SQL Server clients

To connect to an MSSQL database

on Macintosh

on Windows

Connect the Portainer Server to an existing Portainer Agent

With Portainer we can monitor multiple Docker Swarms from one Portainer Server. To connect an existing Portainer server to an agent

Configure the Agent

  • For security reasons, by default, the Portainer Agent only accepts connection from the first Portainer Server it encounters. To enable the Portainer Agent to connect to multiple Portainer Servers, add the AGENT_SECRET environment variable to the docker-compose.yml file of the Agent. This is necessary if you launch a Portainer Server on the Docker host and connect to the local Agent to test it. Without specifying the AGENT_SECRET, another Portainer Server cannot connect to the same agent.
  • Publish the Agent port on the host network
    environment:
      # REQUIRED: Should be equal to the service name prefixed by "tasks." when
      # deployed inside an overlay network
      AGENT_CLUSTER_ADDR: tasks.agent
      # AGENT_PORT: 9001
      # LOG_LEVEL: debug
      AGENT_SECRET: my_secret_token
    ports:
      - target: 9001
        published: 9001
        protocol: tcp
        mode: host

Configure the Server

  • Add the AGENT_SECRET environment variable to the docker-compose.yml file of the Server
    environment:
      AGENT_SECRET: my_secret_token

Add the endpoint to the Portainer Server

  • Log into the Portainer Server
  • Navigate to the Endpoints page
  • Click the Add Endpoint button
  • Select the Agent endpoint type
  • Enter the IP address and the port number ( by default 9001 ) of the Portainer Agent