Troubleshooting

. When did this issue begin occurring? - Does this time and date coincide with any other events? . How often does it occur? - Is is continuous or off and on? - If off and on, is there any pattern to the events? - Are there any other events that coincide when the issue occurs? Like backups or peak business hours? . What is the time stamp of the last time this occurred? - Does this time and date coincide with any other events? . Is it the entire system or is it a particular subsystem/application? For example, is the slowness at the console as well as over ssh or is it specific to an action, is it specific to an application, etc? . Does this same performance impact occur when all 3rd party or only certain 3rd party applications are disabled? . Where and how is the performance impact being observed? . Can a complete description of what the performance is supposed be provided? In particular how the expected performance was measured, what the results were, etc . What is the present status of the system? Is it working normally? or is it experiencing any issues? . What type of workload is this system responsible for ordinarily? I.E. Does it host a database, fileserver, or other application? . Were there any power or networking outages reported near the time that this issue occurred? . Do you know of any CPU and/or memory intensive process that could have been running on the system at the time of the issue? . Were there any messages on the console at the time of the issue? If so, can they be provided to the case in their entirety? . Is this system part of a cluster? . Does the issue cause the system to have a vmcore generated? . Were there any recent changes to the hardware/firmware/software recently? If so, when and what was changed?


Please clarify the issue "servers running slow" - Is some process not completing on time? - Are commands issued to the system taking a long time to complete? What benchmark or comparison do you have to indicate that this is a problem? When did this issue begin occurring? Were any hardware or software changes or upgrades made before this issue began? Has the workload on the system changed at all? Is the issue persistent, repeatable, or random? Do you have any other data that may help in our investigation, including screenshots, comparisons indicating the performance loss, etc.

Ansible : snippet

- name: add search path to /etc/resolv.conf
  lineinfile:
    dest: "/etc/resolv.conf"
    backrefs: True
    state: present
    insertbefore: ^nameserver
    regexp: '(^\s*search(\s+(?!\b{{ item }}\b)[\w\.]+)*)\s*$'
    line: '\1 {{ item }}'
  with_items: "{{ searchpath }}"


About regex_replace

var1: ""{{ var2 | regex_replace ('ABC-(\\d.\\d+)', '\\1) }}"

ansible-vault encrypt_string password123 --ask-vault-pass

- name: revert to a snapshot
  vmware_guest_snapshot:
     datacenter:
     hostname: this is vcenter host name
     username:
     password:
     name: this is vm name
     state: revert
     snapshot_name:
  delegate_to: localhost

- name: power on vm
  vmware_guest:
     datacenter:
     hostname: this is vcenter host name
     username:
     password:
     name: this is vm name
     state: poweredon
  delegate_to: localhost

- name: Wait for host to come back
  local_action:
    module: wait_for
      host="{{ inventory_hostname }}"
      port=22
      delay=30
      timeout=300

Openshift

Openshift 3.5 Documentation: https://access.redhat.com/documentation/en/openshift-container-platform/?version=3.5
Release notes: https://access.redhat.com/documentation/en-us/openshift_container_platform/3.5/html-single/release_notes/#release-notes-ocp-3-5-release-notes
Upgrading: https://access.redhat.com/documentation/en-us/openshift_container_platform/3.5/html-single/installation_and_configuration/#install-config-upgrading-index
Scaling and Performance: https://access.redhat.com/documentation/en-us/openshift_container_platform/3.5/html-single/scaling_and_performance_guide/

Kickstart

PXE doc

http://www.pix.net/software/pxeboot/archive/pxespec.pdf

Understanding PXE Booting and Kickstart Technology

https://docs.oracle.com/cd/E24628_01/em.121/e27046/appdx_pxeboot.htm#EMLCM12198

PXE works with Network Interface Card (NIC) of the system by making it function like a boot device. The PXE-enabled NIC of the client sends out a broadcast request to DHCP server, which returns with the IP address of the client along with the address of the TFTP server, and the location of boot files on the TFTP server. The following steps describe how it works:

 

1. Target Machine (either bare metal or with boot sector removed) is booted.
2. The Network Interface Card (NIC) of the machine triggers a DHCP request.
3. DHCP server intercepts the request and responds with standard information (IP, subnet mask, gateway, DNS etc.). In addition, it provides information about the location of a TFTP server and boot image (pxelinux.0).
4. When the client receives this information, it contacts the TFTP server for obtaining the boot image.
5. TFTP server sends the boot image (pxelinux.0), and the client executes it.
6. By default, the boot image searches the pxelinux.cfg directory on TFTP server for boot configuration files on the TFTP server using the following approach:
   First, it searches for the boot configuration file that is named according to the MAC address represented in lower case hexadecimal digits with dash separators. For example, for the MAC Address "88:99:AA:BB:CC:DD", it searches for the file 01-88-99-aa-bb-cc-dd.
   Then, it searches for the configuration file using the IP address (of the machine that is being booted) in upper case hexadecimal digits. For example, for the IP Address "192.0.2.91", it searches for the file "C000025B".
   If that file is not found, it removes one hexadecimal digit from the end and tries again. However, if the search is still not successful, it finally looks for a file named "default" (in lower case).
   For example, if the boot file name is /tftpboot/pxelinux.0, the Ethernet MAC address is 88:99:AA:BB:CC:DD, and the IP address 192.0.2.91, the boot image looks for file names in the following order:

   /tftpboot/pxelinux.cfg/01-88-99-aa-bb-cc-dd
   /tftpboot/pxelinux.cfg/C000025B
   /tftpboot/pxelinux.cfg/C000025
   /tftpboot/pxelinux.cfg/C00002
   /tftpboot/pxelinux.cfg/C0000
   /tftpboot/pxelinux.cfg/C000
   /tftpboot/pxelinux.cfg/C00
   /tftpboot/pxelinux.cfg/C0
   /tftpboot/pxelinux.cfg/C
   

7. The client downloads all the files it needs (kernel and root file system), and then loads them.
8. Target Machine reboots.
   The Provisioning application uses Redhat's Kickstart method to automate the installation of Redhat Linux on target machines. Using kickstart, the system administrator can create a single file containing answers to all the questions that will usually be asked during a typical Red Hat Linux installation.
   The host specific boot configuration file contains the location of the kickstart file. This kickstart file would have been created earlier by the stage directive of the OS image based on the input from user.

Kickstart sequence of events
http://www.linux-mag.com/id/6747/

A network-based kickstart can be initiated by an PXE Boot capable network card. The PXE Boot first requests an IP address from a DHCP server. It also obtains the location of a PXE Boot file from the DHCP server. PXELINUX is a bootloader for Linux using the PXE network booting protocol. The PXE Boot file is loaded from the TFTP server along with the contents of a file which defines the location and name of the installation kernel and initrd.img file as well as some parameters for the boot kernel and a menu for the Anaconda installer. This configuration file for Anaconda also contains the location of the kickstart configuration file to be used during the installation. 

The PXE Boot file then loads the boot kernel and initrd image still using TFTP. After booting, Anaconda is started and Anaconda loads the menu and displays a window with a timer with several menu options. The Menu and time-out can be skipped if you do not need to make any choices here. 

After choosing the desired kickstart installation, Anaconda locates the kickstart configuration file from the HTTP server and reads it. The kickstart configuration file has a default name of ks.cfg, but can be named anything. We use several for our different configurations, so provide unique names for each. If all of the data required to perform a complete installation is included in the kickstart configuration file, the installation completes without further intervention from the administrator. The RPM files used during the installation are downloaded from the HTTP server as they are needed.

The kickstart configuration file can also contain bash script commands that can be run both before and after the rest of the installation. We make extensive use of the post-installation bash scripts to perform installations of locally required RPM packages and tarballs as well as to make configuration changes before the first reboot.

Cloud

Cloud computing is a model for enabling ubiquitous, convenient, on-demand network access to a shared pool of configurable computing resources (networks, servers, storage, applications, and services) that can be rapidly provisioned and released with minimal management effort or service provider interaction (NIST)

Why Private Cloud?
Higher security and privacy
More Control
Higher cost efficiency
Higher energy efficiency
Improved reliability
Immutable infrastructure
No lock-in

Python

https://github.com/beepscore/PythonLynda

https://developers.google.com/edu/python/regular-expressions

Python design pattern
https://www.youtube.com/watch?v=Er5K_nR5lDQ

Python intro
https://www.youtube.com/watch?v=Oe6rHPmFY3o&index=1&list=PLVxFQjPUB2cnYGZPAGG52OQc9SpWVKjjB

Design Patterns

https://github.com/faif/python-patterns


Creational , Ploymorphism

Factory : Uncertain in types of objects, Decisions to be made at runtime regarding what classes to use

Singleton: Only one instance, Global variable in an object-oriented way, An information case, shared by multiple objects

Builder: Director, Abstract Builder : interfaces, Concrete Builder: implements the interfaces, Product : object being built, divide and conquer strategy

Prototype: (Creating many identical objects individually is expensive. Cloning is an alternative) Create a prototypical instance first. Simply clone it whenever you need replica.


Structural, Inheritance

Decorator: New features to an existing object, Dynamic changes, Not using subclassing.

Proxy: Postpone object creation unless absolutely necessary. Find a placeholder.

Adapter: Incompatible interfaces

Composite: Recursive tree structure. Component(abstract class), Child (concrete class), Composite(concrete class)

Bridge: Two unrelated, parallel, or orthogonal abstractions. One is implementation specific. The other is implementation independent.

Behavioral, Methods and their signatures

Observer: establishes a one-to-many relationship between a subject and multiple observers. Subjects to be monitored. Observers to be notified.

Visitor: allows adding new features to an existing class hierarchy without changing it.

Iterator: allows a client to have sequential access to the elements of an aggregate object without exposing its underlying structure.

Strategy: offers a family of interchangeable algorithms to a client. The problem we often see is that there is a need for dynamically changing the behavior of an object.

Chain of responsibility: opens up various possibilities of processing for a given request. Decouples the request and its processing.


Coupling and Cohesion
Coupling: The degree to which your software elements are connected
Cohesion: The degree of independence
The goal of design patterns: More cohesion and less coupling

Security

https://www.ietf.org/rfc/rfc2828.txt

5 services
1 Confidentiality : Protects data against unauthorized disclosure. Use encryption.
2 Integrity: Ensures data has not been changed, destroyed, or lost in an unauthorized or accidental manner. Use a hash function.
3 Accountability: Accountability directly supports non-reputation and provides protection against false denial of involvement in a communication. Use a digital signature.
4 Authentication: Confirm identity of a system entity. Use a Message Authentication Code (MAC)
5 Availability: Services are accessible and available to authorized users or processes in an information infrastructure. Difficult to protect. ex. Denial of Service attack.

Of the five services, four can be achieved by using encryption. That is why cryptography and network security go hand in hand.