Cloud Init Sample code Repo

1. AWS EC2 Instance creation with cloud-init script passed as user_data

Goal

• The repo can be used to create the bulk instances, applied with similar config across all the instances.
• In case the instances needed to be updated with new config, it can be updated in Chef recipe or Ansible playbook (push the code to git, after the change).
  
• Then we can terminate all previously created instances and then can re-create the instances in bulk by simply executing the script.
  
• Hence achieving the goal of "Cattle" instance provisioning.
  

create_instance.sh is the wrapper script which does the following

• Creates 'n' number EC2 instances of type t2.micro with RHEL 7 OS
  
• Each instance will be having below configurations set when the instances creation is completed
  
  • Set a hostname on operating system level
    
  • Install a package called “my-monitoring-agent”. Assume that the package repository is already configured
    
  • Set the hostname in the configuration of the monitoring agent. Config file located at “/etc/mon-agent/agent.conf”
    
  • Ensure that the two users exists and are part of the group “my-staff”
    
• Also the instances will be assigned with tag name 'DEMO', so all instances will be grouped under the tag and can be deleted easily

Script functionality

• Create_instance.sh script uses the AWS CLI command to invoke the resource creation in AWS.
• The AWS CLI command for instance creation is aws ec2 run-instance.
• We are sending the Cloud-init script file to AWS CLI user-data option. It contains the bash script and is executed by Cloud-init process when the EC2 instance is created.
• System config could be set using different technologies like Chef or Ansible. So I've created two different Cloud-init scripts to show the possibility of using the same AWS resource creation script with our choice of config management tool passed an option to the script. (refer example below).

Chef way

• The cloud_init_chef.txt is a shell script and has the code for installing the required installers, checking out repo from git and running Chef-client command to set the desired VM config

Ansible way

• The cloud_init_ansible.txt is a shell script and has the code for installing the required installers, checking out repo from git and running ansible-playbook command to set the desired VM config

Technologies used

• AWS CLI command for instance creation
  
• Cloud-init script passed in instance creation user_data section
  
• bash shell scripting used to code the cloud-init script
  
• rpm-build used for creation of dummy rpm package <br
• Chef used for setting the required system state
  
• Ansible also used for setting the required system state
  
• Github used as source repo and git commands extensively used while development
  
• Chef-client run in local-mode eliminating the need of Chef server.
  

2. Instance creation steps

Pre-requisite Setup

• AWS CLI setup / config : AWS CLI and Configure CLI
  
• Install Git for Linux using the command yum install git -y or
  
• Git Bash for Windows to access Git repo and to run the shell script in Windows.

Pre-requisite to be done in AWS

• Setup Security group rule for rhel in AWS. In-bound SG rule with SSH port 22 should be enabled.
• Setup AWS keypair to be used for login to instance

Script running procedure (from terminal prompt or Gitbash)

• Clone the cloud_init_sample repo : git clone https://github.com/chefgs/cloud_init_sample
• cd cloud_init_sample
• Fetch the SG-rule name and key-pair name by executing the script ./get_sg_key.sh
• Script takes the below options,
  • Instance count
  • SG rule name
  • AWS key for accessing instance
  • chef or ansible
• Example script execution command structure, ./create_instance.sh 1 rhel_sg_rule myaws_key chef . This command will create 1 EC2 instance of type t2.micro with RHEL OS, with desired state set using Chef
  
• Example script execution command structure, ./create_instance.sh 1 rhel_sg_rule myaws_key ansible . This command will create 1 EC2 instance of type t2.micro with RHEL OS, with desired state set using Ansible
  

3. Terminate Instances

• Run ./terminate_instances.sh . This command will terminate all the instances with tag name "DEMO".

4. Source code repo details making this entire functionality

• I've pushed all the source code in Github,
  AWS CLI instance create repo
  Chef cookbook repo
  Dummy rpm create repo
  

5. Best practices followed

• Cloud-init and Chef run outputs are captured in log to identify any script failures.
• Cloud-init output is redirected to the path /var/log/userdata.out
• Chef-client output is redirected to the path /var/log/chefrun.out
• Shell script has been coded with validation check to avoid the error scenarios
• Chef cookbook coded with below best practices,
  • Variables stored as attributes
  • Gaurd check has been added while installing RPM from local path
• Enough comment has been added in all the scripts for anyone to understand the code.
• Every source code has been preserved in Github SCM.
• Enitre repo detail has been documented in Github readme.

6. Possible alternatives of Chef

• The instance desired state configuration could also be possible with Chef "kind-of" alternative technologies like Puppet or Ansible etc.
• So with the same Cloud-init script structure as a base, it can be modified to alternative Infra as code tool installation and execution.
• One such possibility is depicted in this repo with Chef and Ansible cloud-init scripts

7. Output details

Please refer here for output.