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Ansible/Ansible_install_on_RHEL.MD

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+#### On RHEL 8.x server
+
+1. Install Python latest version  (on Control node and Managed host)
+   ```sh 
+   yum install python3 -y
+   ```
+
+1. By default, python3 is the command to run python commands. to use just python, use "alternatives" command.  (on Control node and Managed host)
+   ```sh 
+   alternatives --set python /usr/bin/python3
+   ```
+
+1. Check for Python version  
+   ```sh 
+   python --version
+   ```
+1. Install python-pip package manager  (on Control node)
+   ```sh 
+   yum -y install python3-pip
+   ```
+
+1. Create a new user for ansible administration & grant admin access to the user  (on Control node and Managed host)
+   ```sh 
+   useradd ansadmin
+   passwd ansadmin
+   ```
+1. Below command adds ansadmin to sudoers file. But we strongly recommended using "visudo" command if you are aware vi or nano editor.  (on Control node and Managed host)
+   ```sh
+   echo "ansadmin ALL=(ALL) NOPASSWD: ALL" >> /etc/sudoers
+   ```
+1. Using key-based authentication is advised. If you are still at the learning stage use password-based authentication (on Control node and Managed host)
+   ```sh 
+   # sed command replaces "PasswordAuthentication no to yes" without editing file 
+    sed -ie 's/PasswordAuthentication no/PasswordAuthentication yes/' /etc/ssh/sshd_config
+    sudo service sshd reload
+   ``` 
+
+    #### Install Ansible as a ansadmin user (on Control node)
+   ```sh 
+   su - ansadmin
+   pip3 install ansible --user
+   ``` 
+      Note: Ansible must be installed as a user (here ansadmin)
+1. check for ansible version 
+   ```sh
+   ansible --version
+   ```
+
+1. Log in as a ansadmin user on master and generate ssh key (on Control node)
+   ```sh 
+   ssh-keygen
+   ```
+1. Copy keys onto all ansible managed hosts (on Control node)
+   ```sh 
+   ssh-copy-id ansadmin@<target-server>
+   ```
+### Validation test
+
+1. Create a directory /etc/ansible and create an inventory file called "hosts" add control node IP address in it. 
+   
+1. Run ansible command as ansadmin user it should be successful (Master)
+   ```sh 
+   ansible all -m ping
+   ```

Ansible/Ansible_installation.MD

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+# Ansible Installation
+
+Ansible is an open-source automation platform. It is very, very simple to set up and yet powerful. Ansible can help you with configuration management, application deployment, task automation.
+
+### Pre-requisites
+
+1. An AWS EC2 instance (on Control node)
+
+### Installation steps:
+#### on Amazon EC2 instance
+
+1. Install python and python-pip
+   ```sh
+   yum install python
+   yum install python-pip
+   ```
+1. Install ansible using pip check for version
+    ```sh
+    pip install ansible
+   ansible --version
+   ```
+   
+1. Create a user called ansadmin (on Control node and Managed host)  
+   ```sh
+   useradd ansadmin
+   passwd ansadmin
+   ```
+1. Below command grant sudo access to ansadmin user. But we strongly recommended using "visudo" command if you are aware vi or nano editor.  (on Control node and Managed host)
+   ```sh
+   echo "ansadmin ALL=(ALL) NOPASSWD: ALL" >> /etc/sudoers
+   ```
+   
+1. Log in as a ansadmin user on master and generate ssh key (on Control node)
+   ```sh 
+   sudo su - ansadmin
+   ssh-keygen
+   ```
+1. Copy keys onto all ansible managed hosts (on Control node)
+   ```sh 
+   ssh-copy-id ansadmin@<target-server>
+   ```
+
+1. Ansible server used to create images and store on docker registry. Hence install docker, start docker services and add ansadmin to the docker group. 
+   ```sh
+   yum install docker
+   
+   # start docker services 
+   service docker start
+   service docker start 
+   
+   # add user to docker group 
+   usermod -aG docker ansadmin
+
+   ```
+1. Create a directory /etc/ansible and create an inventory file called "hosts" add control node and managed hosts IP addresses to it. 
+ 
+### Validation test
+
+   
+1. Run ansible command as ansadmin user it should be successful (Master)
+   ```sh 
+   ansible all -m ping
+   ```

Docker/DockerHub.MD

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+## What is Docker Hub Registry
+
+Docker Hub is a cloud-based registry service which allows you to link to code repositories, build your images and test them, stores manually pushed images, and links to Docker Cloud so you can deploy images to your hosts. It provides a centralized resource for container image discovery, distribution and change management, user and team collaboration, and workflow automation throughout the development pipeline.
+
+##### Ref URL : https://docs.docker.com/docker-hub/
+
+1. Create a docker hub account in https://hub.docker.com/
+
+1. Pull a docker image 
+
+   ```sh 
+   docker pull ubuntu
+   ```
+
+1. pull a docker image with the old version
+
+   ```sh
+   docker pull ubuntu:16.04
+   ```
+
+1. create a custom tag to the docker image
+   ```sh
+   docker tag ubuntu:latest valaxy/ubuntu:demo
+   ```
+
+1. login to your docker hub registry 
+   ```sh
+   docker login
+   docker push valaxy/ubuntu:demo
+   ```
+
+### testing 
+
+1. Remove all images in docker server 
+   ```sh 
+   docker image rm -f <Image_id>
+   ```
+
+1. Pull your custom image from your docker account
+   ```sh
+   docker pull valaxy/ubuntu:demo
+   ```
+

Docker/Docker_Commands.MD

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+
+1. how to search a docker image in hub.docker.com
+```sh
+docker search httpd
+```
+2. Download a docker image from hub.docker.com
+```sh
+docker image pull <image_name>:<image_version/tag>
+```
+
+3. List out docker images from your local system
+```sh
+docker image ls
+```
+
+4. Create/run/start a docker container from image
+```sh
+docker run -d --name <container_Name> <image_name>:<image_version/tag>
+
+d - run your container in back ground (detached)
+```
+
+5. Expose your application to host server
+```sh
+docker run -d  -p <host_port>:<container_port> --name <container_Name> <image_name>:<Image_version/tag>
+
+docker run -d --name httpd_server -p 8080:80 httpd:2.2
+```
+
+6. List out running containers
+```sh
+docker ps
+```
+
+7. List out all docker container (running, stpooed, terminated, etc...)
+```sh
+docker ps -a
+```
+
+8. run a OS based container which interactive mode (nothing but login to container after it is up and running)
+
+```sh
+docker run -i -t --name centos_server centos:latest
+i - interactive
+t - Terminal
+```
+
+9. Stop a container 
+```sh
+docker stop <container_id>
+```
+
+10. Start a container which is in stopped or exit state
+
+```sh
+docker start <container_id>
+```
+11. Remove a container
+
+```sh
+docker rm <container_id>
+```
+
+12. login to a docker container
+```sh
+docker exec -it <container_Name> /bin/bash
+```

Docker/Docker_Installation_Steps.MD

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+# Installing Docker on Amazon Linux server
+
+### Pre-requisites
+1. Amazon Linux EC2 Instance
+
+## Installation Steps
+
+1. Install docker and start docker services
+   ```sh 
+   yum install docker -y
+   docker --version 
+   
+   # start docker services
+   service docker start
+   service docker status
+   ```
+1. Create a user called dockeradmin
+   ```sh
+   useradd dockeradmin
+   passwd dockeradmin
+   ```
+1. add a user to docker group to manage docker 
+   ```
+   usermod -aG docker dockeradmin
+   ```
+### Validation test
+1. Create a tomcat docker container by pulling a docker image from the public docker registry
+   ```sh
+   docker run -d --name test-tomcat-server -p 8090:8080 tomcat:latest
+   ```
+
+## Docker Installation on CentOS server
+##### Referance URL : https://docs.docker.com/install/linux/docker-ce/centos/#install-using-the-repository
+### Pre-requisites
+
+Please follow below steps to install docker CE on CentoOS server instance. For RedHat only Docker EE available 
+
+1. Install the required packages.
+
+   ```sh 
+   sudo yum install -y yum-utils \
+   device-mapper-persistent-data \
+   lvm2
+   ```
+  
+1. Use the following command to set up the stable repository.
+ 
+   ```sh 
+   sudo yum-config-manager \
+   --add-repo \
+   https://download.docker.com/linux/centos/docker-ce.repo
+   ```
+
+### INSTALLING DOCKER CE
+
+1. Install the latest version of Docker CE.
+   ```sh 
+   sudo yum install docker-ce
+   ```
+
+   Note: If prompted to accept the GPG key, verify that the fingerprint matches 
+060A 61C5 1B55 8A7F 742B 77AA C52F EB6B 621E 9F35, and if so, accept it.
+
+1. Start Docker.
+   ```sh 
+   sudo systemctl start docker
+   ```
+
+1. Verify that docker is installed correctly by running the hello-world image.
+   ```sh
+   sudo docker run hello-world
+   ```

Docker/Dockerfile_Instructions.md

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+
+DockerFile 
+
+1. A Dockerfile is a text document that contains all the commands a user could call on the command line to assemble an image.   
+2. The docker build command builds an image from a Dockerfile and a context.  
+ ```sh 
+  docker build .
+  docker build -f /path/to/a/Dockerfile .
+  docker build -t shykes/myapp .
+ ```
+
+3. The Docker daemon runs the instructions in the Dockerfile one-by-one, committing the result of each instruction to a new image if necessary, before finally outputting the ID of your new image.  
+4. Whenever possible, Docker uses a build-cache to accelerate the docker build process significantly.  
+5. When you’re done with your build, you’re ready to look into scanning your image with docker scan  
+ ```sh
+ docker scan hello-world
+ 
+ ```
+
+## Dockerfile Creation  
+
+ Docker file format
+  ```sh
+   # Comment
+   INSTRUCTION arguments
+  ```
+
+1. A Dockerfile must begin with a FROM instruction.  
+
+2. Docker distributes official versions of the images that can be used for building Dockerfiles under docker/dockerfile repository on Docker Hub.
+
+- `FROM` - A valid Dockerfile must start with a FROM instruction.
+
+- `RUN` - The RUN instruction will execute any commands in a new layer on top of the current image and commit the results. The resulting committed image will be used for the next step in the Dockerfile.
+
+- `CMD` - The main purpose of a CMD is to provide defaults for an executing container. 
+
+   `Note:` There can only be one CMD instruction in a Dockerfile. If you list more than one CMD then only the last CMD will take effect.
+
+   `Note` - Do not confuse RUN with CMD. RUN actually runs a command and commits the result; CMD does not execute anything at build time, but specifies the intended command for the image.
+
+- `LABEL` -The LABEL instruction adds metadata to an image. A LABEL is a key-value pair. T
+
+- `EXPOSE`
+  1. The EXPOSE instruction informs Docker that the container listens on the specified network ports at runtime. 
+  2. To set up port redirection on the host system, see using the -P flag.
+  3. The docker network command supports creating networks for communication among containers without the need to expose or publish specific ports, because the containers connected to the network can communicate with each other over any port. 
+
+- `ENV` - The ENV instruction sets the environment variable <key> to the value <value>.
+
+- `ADD` - The ADD instruction copies new files, directories or remote file URLs from <src> and adds them to the filesystem of the image at the path <dest>.
+
+    If <src> is a local tar archive in a recognized compression format (identity, gzip, bzip2 or xz) then it is unpacked as a directory. 
+
+- `COPY` - The COPY instruction copies new files or directories from <src> and adds them to the filesystem of the container at the path <dest>.
+
+- `ENTRYPOINT` - An ENTRYPOINT allows you to configure a container that will run as an executable.
+
+  1. ENTRYPOINT will override all elements specified using CMD
+  2. Both CMD and ENTRYPOINT instructions define what command gets executed when running a container. There are few rules that describe their co-operation.
+
+  3. Dockerfile should specify at least one of CMD or ENTRYPOINT commands.
+
+  4. ENTRYPOINT should be defined when using the container as an executable.
+
+  5. CMD should be used as a way of defining default arguments for an ENTRYPOINT command or for executing an ad-hoc command in a container.
+
+  6. CMD will be overridden when running the container with alternative arguments.
+
+- `VOLUME` - The VOLUME instruction creates a mount point with the specified name and marks it as holding externally mounted volumes from native host or other containers. 
+
+- `USER` - The USER instruction sets the user name to use when running the image
+- `WORKDIR` - The WORKDIR instruction sets the working directory for any RUN, CMD, ENTRYPOINT, COPY and ADD instructions
+
+- `ARG` - The ARG instruction defines a variable that users can pass at build-time to the builder with the docker build command using the --build-arg <varname>=<value> flag. 
+
+- `SHELL` - The SHELL instruction allows the default shell used for the shell form of commands to be overridden. 
+
+