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90 Days of DevOps

A list of videos / courses I have completed and my learnings.

Prerequisites

DevOps Prerequisites Course - Getting started with DevOps

Things learnt I this video

Linux basics

  • echo - prints to screen
  • ls - lists files and folders
  • cd - change directory
  • pwd - prints working directory
  • mkdir - makes a directory
  • hostname - prints the hostname

Directories

  • cd new-dir; mkdir www; pwd - changes to new-dir creates dir www and prints working directory
  • mkdir -p /tmp/hello/world - creates whole dir stucture the -p flag means: “create the parent directories, too”
  • rm -r /tmp/my-dir - removes the directory the -r flag means: to work recursively
  • cp -r my-dir /tmp/my-dir - copy directory to a new location -r allows copying of whole directory

Files

  • touch <filename> - creates blank file
  • cat > test.txt - allows you to add contents to file press ctl-d to exit...better to use vim IMO.
  • cat test.txt - shows you contents of file
  • cp test.txt backup-test.txt - copies the contents of file and creates a new one <orignal> <copy>
  • mv test.txt new-test.txt - renames the file (unless specifying a dir)

User accounts

  • whoami - prints our current user to the terminal
  • id - prints out more information about current user
  • su <user> - switch to a different user
  • ssh <user>@123.123.123.0.0 - ssh into a server as a different user

Download files

  • curl <some url> -O - downloads a file using curl the -O flags allows the saving of file.
  • wget <some url> -O <file name> - same as above but allows you to name it.

Check OS version

  • ls /etc/*release* - inspects the release files
  • cat /etc/*release* - allows more info

Package managers

RPM (RedHat package manager)

rpm doesnt install dependencies

  • rpm -i someapp.rpm - installs package
  • rpm -e someapp.rpm - uninstalls package
  • rpm -q someapp.rpm - queries package

YUM

  • yum install someapp - YUM will install someapp and all it's dependencies
  • yum repolist - lists all the yum repos example output below:
repo id                                                repo name                                                               status
VMware-tools-collection                                VMware-tools-collection                                                     41
base/7/x86_64                                          CentOS-7 - Base                                                         10,072
docker_ce/x86_64                                       Docker CE Stable - x86_64                                                  169
elastic-7.x                                            Elastic repository for 7.x packages                                      1,404
epel/x86_64                                            Extra Packages for Enterprise Linux 7 - x86_64                          13,752
extras/7/x86_64                                        CentOS-7 - Extras                                                          516
!icinga-stable-release/7                               icinga-stable-release                                                    1,309
!icinga-stable-release-tests/7                         icinga-stable-release-tests                                              1,309
!pulsepoint                                            PulsePoint                                                               2,312
puppet6/x86_64                                         Puppet 6 Repository el 7 - x86_64                                          358
rsyslogall/7/x86_64                                    rsyslog                                                                  3,075
trivy/7/x86_64                                         Trivy repository                                                           100
updates/7/x86_64                                       CentOS-7 - Updates                                                       4,244
  • ls /etc/yum.repos.d - lists all the repos and their config files
  • cat /etc/yum.repos.d/<repo file> - shows the url of where the packages of repo are install - example output:
[docker_ce]
name=Docker CE Stable - $basearch
baseurl=https://download.docker.com/linux/centos/7/$basearch/stable
enabled=1
gpgcheck=1
gpgkey=https://download.docker.com/linux/centos/gpg
  • yum list - shows all installed packages
  • yum remove <package> - removes package
  • yum --showduplicates list <package> - lists all avaiable packages for <package>
  • yum install <package>.0.0.1 - installs a package from a certain version

Services

  • service <service> start - will start a service
  • service <service> status - will give the status of the service

Linux networking

Hooking the VM to your DNS server, use the following for example. Adding this in the host.

cat /etc/resolv.conf

nameserver 192.168.1.100

Giving the ability to ping subdomain urls by their subdomain name. For example if were to have web.company.com but you wanted to ping this by using ping web it would fail.

To resolve this add search company.com into your /etc/resolv.conf file on the host.

nslookup option description
-domain=[domain name] Change the default DNS name.
-debug Show debugging information.
-port=[port-number] Specify the port for queries. The default port number is 53.
-timeout=[seconds] Specify the time allowed for the server to respond.
-type=a View information about the DNS A address records.
-type=any View all available records.
-type=hinfo View hardware-related information about the host.
-type=mx View Mail Exchange server information.
-type=ns View Name Server records.
-type=ptr View Pointer records. Used in reverse DNS lookups.
-type=soa View Start of Authority records.

The dig <some ip> will give you more information on that IP address

Running the route command will display the Kernels latest routing table and allow you to see the current routing config

To add a gateway from one network to another you can run the ip route add command for example:

Network 1 = 192.168.1.0
Network 2 = 192.168.2.0

ip route add 192.168.2.0/24 via 192.168.1.1

Will allow network 2 to speak to network 1 via the gateway on network 1

For any network you don't know a route too you can use is address as the default gatwway

ip route add default via 192.168.2.1: for example

Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
default         192.168.2.1     0.0.0.0         UG    0      0        0 eth0

You could also use 0.0.0.0 instead of default which means any IP destination. Having 0.0.0.0 as a gateway means it does not require one as its on an internal network.

ip command description
ip List and modify interfaces on the host
ip addr See the IP addresses asigned to the interfaces
ip route / route Provides the routing table

All changes with above commands are only valid till a reboot. These would have to be set in certain files like /etc/sysctl.conf for forwarding.

CCNA

A network is considred to be a group of IP addresses, where a router is needed to connect different networks. Or a switch to extend the items in the current network.

Switches

  • Layer 1 addresses are subject to change, anything physically plugged in
  • Layer 2 are mac addresses these will never change

Get access to the mac address table on a Cisco switch

Switch> enable
Switch# show mac-address-table
  • Q: Which of the following addresses will a switch use to populate a CAM table
  • A: source MAC address

A switch will use source Media Access Control (MAC) addresses to populate the Content Addressable Memory (CAM) table. The CAM table, which is also called the 'switching table' is used by a switch to discorver the relationship between the Open Systems Interconnection (OSI) Layer 2 addres of a device and the physical port used to reach the device. The switch populates the CAM table by recording the source MAC address of an inbound Layer 2 frame and the corresponding switch port that the frame arrived on.

  • Q: Which of the following addresses will a switch use to make forwarding decisions?
  • A: destination MAC address

A switch will use destination MAC addresses to make forwarding descision. Swiches make forwarding decisions base on the destintion MAC address contained in the frame's header. The swich first searches the CAM table for an entry that maches the frame's destination MAC address. The CAM table, which is also called the switching table, used by a switch to discover the relationship between Layer 2 address of a device and the physical port used to reach the device. If the frame's desitnation MAC address is not found in the table, the switch forwards the frame to all its ports. except the port from which it recieved the frame. If the destination MAC address is found in the table, the switch forwards the frame to the appropriate port. The source MAC address is also recorded if it did not previously exist in the CAM table.

Routers

Routers are designed to connect networks together.

TCP/IP - OSI

See more here

TCP/IP Model
TCP/IP description
Application Layer 7 - Interaction layer where apps can access network services
Transport Transmits data using TCP / UDP protcol
Network Layer 3 - IP addresses assigned
Data Link Layer 2 - MAC addresses
Physical Layer 1 - Eth cables / NIC / Physical inputs
OSI Model
TCP/IP description
Application Layer 7 - Interaction layer where apps can access network services
Presentation Ensures data is in a usable format
Session Maintains connections controllong ports / sessions
Transport Transmits data using TCP / UDP protcol
Network Layer 3 - IP addresses assigned
Data Link Layer 2 - MAC addresses
Physical Layer 1 - Eth cables / NIC / Physical inputs

Remembering the OSI model: All People Seem To Need Data Processing / Please Do Not Throw Sausage Pizza Away

  • Q: Which of the following operates primarily at Layer 2 on the OSI model?
  • A: a switch

A switch operates primarily at Layer 2 of the OSI mode. Switches operator on the Data Link layer. Where as a router operators on a Layer 3

  • Q: Which of the following operate primarily at the Physical Layer of the OSI model?
  • A: repeaters & hubs
What connects to what...
Device description
Switches Layer 2
Routers Layer 3
Hubs Layer 1

Git

Docker

Kubernetes

CI/CD

IAC tools

Observability

Chaos engineering

Policy engines

Servicemesh