Crash loop back in dockers and kubernetes

 In a Docker or Kubernetes environment, a crash loop back can occur when a container or pod is unable to start properly and continuously restarts. This can be caused by a variety of issues, such as an incorrect configuration, insufficient resources, or a bug in the application or container image.

To troubleshoot a crash loop back in a Docker container, you can check the container logs for error messages, inspect the container's environment variables and configuration, and verify that the container has the necessary resources.

In Kubernetes, you can use the kubectl command-line tool to check the status of the pod and view its logs. You can also use the Kubernetes dashboard to view the pod's details and troubleshoot the issue. Additionally, you can use the command "kubectl describe pod <pod-name>" to get the detailed description of the pod.

If the issue persists, you may need to update the container image, scale up the resources allocated to the pod, or seek professional help.

what is an API

 An API (Application Programming Interface) is a set of rules and protocols for building and interacting with software applications. It is a set of clearly defined methods of communication between various software components.

APIs allow different software systems to communicate with each other, enabling them to share data and functionality. For example, an API can allow a mobile application to access data from a web-based service, or it can allow a website to access data from a third-party service.

APIs can be classified into several types, including:

Web-based APIs: These are the most common type of APIs and are typically based on the HTTP protocol. They can be accessed over the internet using standard web technologies such as HTTP and HTTPS.

Database APIs: These APIs provide a way to interact with a specific database and perform operations such as reading and writing data.

Operating system APIs: These APIs provide a way to interact with the underlying operating system and perform tasks such as reading and writing files, starting and stopping processes, and managing system resources.

Library APIs: These APIs provide a way to interact with a specific library or module and perform tasks such as reading and writing data, or calling specific functions or methods.

APIs are typically designed to be easy to use and understand, and they often come with documentation that describes how to use them.

APIs are widely used in modern software development, they enable a wide range of capabilities such as integration, automation, and connecting to different services and platforms. With the increasing use of microservices architecture, APIs have become even more important as they allow different parts of an application to communicate and exchange data with each other.

What is devops

 DevOps is a set of practices and tools that aims to improve collaboration and communication between development and operations teams in order to deliver software and services more quickly, reliably and securely. It is a culture and mindset that emphasizes automation, collaboration and monitoring throughout the software development lifecycle.

DevOps practices include:

Continuous Integration (CI): This practice involves integrating code changes from multiple developers into a single codebase as frequently as possible. This allows teams to catch and resolve conflicts early on and ensure that the codebase is always in a releasable state. Tools like Git, Jenkins, and TravisCI are commonly used for continuous integration.

Continuous Delivery (CD): This practice involves automating the process of building, testing, and deploying software to production. This allows teams to release new features and updates faster and more frequently, with less risk and downtime. Tools like Jenkins, TravisCI, and AWS CodePipeline are commonly used for continuous delivery.

Configuration Management: This practice involves using tools like Ansible, Puppet, or Chef to manage and automate the configuration of servers and infrastructure. This allows teams to easily provision, configure, and scale infrastructure as needed.

Containerization: This practice involves using technologies like Docker to package and deploy applications and services in a consistent and portable way. This allows teams to easily move applications between different environments and ensure consistency across different stages of the development lifecycle.

Monitoring and Logging: This practice involves using tools like Prometheus, Grafana, and ELK to collect and analyze data about the performance and health of software and infrastructure. This allows teams to quickly identify and resolve issues and improve overall system performance.

DevOps also promotes a culture of collaboration, communication, and experimentation. This allows teams to work more closely together, share knowledge and learn from each other.

The goal of DevOps is to break down silos between development and operations teams and enable them to work together to achieve a common goal: delivering value to customers quickly, reliably and securely. This allows organizations to respond faster to changing business requirements and improve overall business agility.

It's worth noting that DevOps is a continuous process of improvement and learning, it's not a one-time implementation, but a journey that organizations take to improve their software delivery and operations.

Complete DevOps:--->

Complete DevOps is an end-to-end approach to software development and delivery that spans the entire software development lifecycle. It encompasses all aspects of software development, from idea generation, to planning, development, testing, deployment and ongoing maintenance.

Complete DevOps includes:

Collaboration and communication across all teams involved in software development, including development, operations, security, and business teams.

Automation of all aspects of software development and delivery, including continuous integration, continuous delivery, infrastructure as code, and configuration management.

Monitoring and logging of all aspects of software and infrastructure to provide visibility into system performance and identify issues quickly.

Emphasis on security and compliance, including security testing and automated security controls.

Use of agile methodologies and practices to promote flexibility, experimentation, and continuous improvement.

A complete DevOps approach also includes a focus on culture and people. This includes fostering a culture of collaboration, experimentation, and continuous learning. It also involves providing the necessary tools, training, and resources to enable teams to work effectively and efficiently.

The goal of complete DevOps is to deliver software and services more quickly, reliably and securely. This allows organizations to respond faster to changing business requirements and improve overall business agility. By automating and streamlining the software development lifecycle, organizations can also increase efficiency and reduce costs while improving the overall quality of their software.

A Proxy

A proxy is a computer or a software program that acts as an intermediary between a client and a server. The client sends a request to the proxy, and the proxy then forwards the request to the server. The server's response is then sent back through the proxy to the client.

Proxies are typically used for one or more of the following purposes:

To improve performance by caching frequently requested content

To filter or block unwanted traffic

To hide the client's IP address or other identifying information

To bypass geographical restrictions or internet censorship

To provide anonymity and security by encrypting the communication between the client and the proxy

There are several types of proxies, including:

HTTP proxy: used to handle HTTP requests and responses

SOCKS proxy: used to handle any type of network traffic

Transparent proxy: a type of proxy that does not modify the request or response headers, and is typically used for caching or filtering

Anonymous proxy: a type of proxy that modifies the request headers to remove identifying information

Elite proxy: a type of proxy that provides both anonymity and security, typically used to bypass firewalls or for scraping data

It's worth noting that some proxy servers can also function as VPN (Virtual Private Network) servers, allowing users to securely connect to a remote network. 

Linux Directory Structure

 Linux Directory Structure:--->

The Linux file system is organised in a hierarchical structure, similar to a tree, with the root directory (/) at the top. All other directories and files are contained within the root directory. The following is a brief overview of the main directories and their purpose in a typical Linux file system:

/ : The root directory is the top-most level of the file system. All other directories and files are contained within the root directory.

/bin : Contains binary executable that are necessary for the system to boot and run in single-user mode.

/sbin : Contains system binary executable that are necessary for the system to boot, run, and maintain a consistent state.

/etc : Contains configuration files for the system and applications.

/usr : Contains user-related data, including applications, libraries, and documentation.

/var : Contains variable data, such as logs, mail, and spool files.

/tmp : Contains temporary files that are not required to persist between system reboots.

/home : Contains the home directories for users.

/opt : Contains optional software packages.

/proc : A virtual file system that provides information about the system's processes and kernel.

/sys : A virtual file system that provides information about the system's hardware and configuration.

Exploring directories and their usability:

We know that Linux is a very complex system that requires an efficient way to start, stop, maintain and reboot a system, unlike Windows operating system. In the Linux system some well-defined configuration files, binaries, man pages information files available for every process. 

Linux Kernel File:

• /boot/vmlinux – The Linux kernel file.

Device Files:

• /dev/hda – Device file for the first IDE HDD.
• /dev/hdc – A pseudo-device that output garbage output is redirected to /dev/null.

System Configuration Files:

• /etc/bashrc – It is used by bash shell that contains system defaults and aliases.
• /etc/crontab – A shell script to run specified commands on a predefined time interval.
• /etc/exports – It contains information on the file system available on the network.
• /etc/fstab – Information of the Disk Drive and their mount point.
• /etc/group – It is a text file to define Information of Security Group.
• /etc/grub.conf – It is the grub bootloader configuration file.
• /etc/init.d – Service startup Script.
• /etc/lilo.conf – It contains lilo bootloader configuration file.
• /etc/hosts – Information of IP and corresponding hostnames.
• /etc/hosts.allow – It contains a list of hosts allowed accessing services on the local machine.
• /etc/host.deny – List of hosts denied to access services on the local machine.
• /etc/inittab – INIT process and their interaction at the various run level.
• /etc/issue – Allows editing the pre-login message.
• /etc/modules.conf – It contains the configuration files for the system modules.
• /etc/motd – It contains the message of the day.
• /etc/mtab – Currently mounted blocks information.
• /etc/passwd – It contains username, password of the system, users in a shadow file.
• /etc/printcap – It contains printer Information.
• /etc/profile – Bash shell defaults.
• /etc/profile.d –  It contains other scripts like application scripts, executed after login.
• /etc/rc.d – It avoids script duplication.
• /etc/rc.d/init.d – Run Level Initialisation Script.
• /etc/resolv.conf – DNS being used by System.
• /etc/security – It contains the name of terminals where root login is possible.
• /etc/skel – Script that initiates new user home directory.
• /etc/termcap – An ASCII file that defines the behavior of different types of the terminal.
• /etc/X11 –  Directory tree contains all the conf files for the X-window System.

User Related Files:

• /usr/bin – It contains most of the executable files.
• /usr/bin/X11 – Symbolic link of /usr/bin.
• /usr/include – It contains standard include files used by C program.
• /usr/share – It contains architecture independent shareable text files.
• /usr/lib – It contains object files and libraries.
• /usr/sbin – It contains commands for Super User, for System Administration.

Virtual and Pseudo Process Related Files:

• /proc/cpuinfo – CPU Information
• /proc/filesystems – It keeps the useful info about the processes that are running currently.
• /proc/interrupts – it keeps the information about the number of interrupts per IRQ.
• /proc/ioports – Contains all the Input and Output addresses used by devices on the server.
• /proc/meminfo –  It reports the memory usage information.
• /proc/modules – Currently using kernel module.
• /proc/mount – Mounted File-system Information.
• /proc/stat –  It displays the detailed statistics of the current system.
• /proc/swaps –  It contains swap file information.

Version Information File:

• /version – It displays the Linux version information.

Log Files:

• /var/log/lastlog – It stores user last login info.
• /var/log/messages – It has all the global system messages.
• /var/log/wtmp – It keeps a history of login and logout information

[RHEL8] Redhat Pacemaker PCS Cluster

History of PCS:--->

PCS (Pacemaker Configuration System) is a command line and web-based interface for configuring and managing Pacemaker clusters. It was first introduced as a part of the Pacemaker project, which was started in the year 2005 by Linux-HA (Linux High Availability) community. PCS was designed to provide a more user-friendly interface for performing common cluster operations and to simplify the process of creating and maintaining a cluster configuration.

In the year 2010, PCS was included as a part of Red Hat Enterprise Linux (RHEL) 6 and also in various other Linux distributions. Over the years, PCS has gone through various updates and new features were added to it. With each new release, it has become more robust, secure, and easy to use.

With the release of RHEL 8 and later, PCS was re-designed with new features and improvements, such as support for new platforms, improved security, and enhanced scalability.

PCS is also an open-source software and it is actively being developed and maintained by the Linux-HA community and Red Hat. It is widely used by organizations and IT administrators to manage and maintain high availability clusters in their production environments.

Redhat Pacemaker PCS Cluster:--->

Red Hat Pacemaker is a cluster resource manager for Linux-based systems. It is used to create and manage highly-available clusters by controlling the start, stop, and failover of resources such as services and virtual IP addresses. PCS (Pacemaker Configuration System) is a command line and web-based interface for configuring and managing Pacemaker clusters. It provides a simplified way to create, manage and maintain a cluster configuration, as well as a more user-friendly interface for performing common cluster operations. Together, Pacemaker and PCS are a powerful tool for creating and managing highly-available clusters on Red Hat Enterprise Linux.

Failover of resources such as services and virtual IP addresses:--->

Failover in the context of Pacemaker and PCS refers to the process of automatically switching over to a secondary resource or node in the event of a failure or outage of the primary resource or node. This ensures that the service or resource remains available and accessible to users, even if one of the nodes or resources in the cluster goes down.

For example, a service such as a web server may be running on a primary node in a cluster. If that primary node goes down, Pacemaker will automatically failover to a secondary node, ensuring that the web server is still available for users to access. Similarly, a virtual IP address can be configured to failover to a secondary node in the event that the primary node it is associated with goes down.

Failover in Pacemaker and PCS is achieved through the use of "resources" and "resource agents". Resources are the services and resources that are being managed by Pacemaker (such as a web server, database, or virtual IP address), and resource agents are scripts that are used to control the behavior of those resources (such as starting, stopping, or checking the status of a service).

Intro-Linux

Linux is an open-source operating system that was first introduced in 1991 by Linus Torvalds. It is based on the Unix operating system and is known for its stability, security, and flexibility. Linux is used by individuals, businesses, and governments around the world, and is a popular choice for servers, supercomputers, and mobile devices.

One of the greatest benefits of using Linux is its open-source nature, which means that the source code is freely available for anyone to use, modify, and distribute. This has led to a large and active community of developers who contribute to the development and maintenance of the operating system.

Another benefit of Linux is its compatibility with a wide range of hardware. Linux can run on everything from small embedded devices to powerful servers, and can be customised to fit the specific needs of the user.

Additionally, Linux is known for its security features, such as built-in firewalls and file permissions. This makes it a popular choice for servers and other critical systems that need to be protected from outside threats.

Overall, Linux is a powerful and versatile operating system that offers a wide range of benefits for users. Whether you're a small business owner, a developer, or a home user, there's a version of Linux that can meet your needs.