DevOps Classroom Series – Chef – 19/Nov/2019

Configuration Management

Example Scenario

• Developer => submits code to git (VCS)
• CI/CD Engine picks up the code and does build/package
• CI/CD Engine Executes the Unit Tests
• CI/CD Engine needs to create Test Environments (System Test/Load Test/Performance Test) and execute the test cases
• Once tests are successful then post approval , you go live.

Creating Environments

• Creating Environments is Deploying applications into servers.
• It might also include creating virtual Servers

Sample Java Based application

• Developer commits the Code
• Build and package is done by build tools like maven mvn package
• Result of Build/Package will be a file with jar/war extension
• To deploy application in server
  • Pre-requisites:
    • JDK 1.8 needs to be Installed
    • tomcat 8 needs to be installed
  • Deployment
    • Copy the package into some folder
    • restart tomcat
  • Post-Deployment:
    • Clean up temp directories

Possible ways of deployment

• Manual:

  • Administrator executes the pre-requisites, deployment and post-deployment steps
  • Problems:
    • Time Consuming
    • Humans are not good at repetition
    • We cannot guarantee all admins will give same result

• Scripting:

  • We tend to write shell/PowerShell scripts to solve the deployment
  • In scripts we write instructions about how the deployment has to be done
  • Problems:
    • Scripting is generally based out of assumptions
    • Scripting is mostly unreadable.

• Configuration Management:

  • We use Declarative Way, which means you will write what has to done but not how it has to done
  • CM scripts are idempotent. Executing CM Scripts will always give the same state
  • In CM you write the desired state to be achieved.
  • Problems:
    • Learning Curve

Configuration Management Architecture

• Configuration Management Server:

  • This server has CM scripts all the necessary infrastructure.

• Nodes:

  • These are servers/machines where you want to apply configuration

• Models:

  • Push: In case of Push based CM, Server will initiate communications to the nodes
  • PULL: In this case, nodes will initiated communications with the server.

PULL Based Configuration Management.

• Agent:
  • Agent has to installed on all the nodes.
  • Agent will have information about server
  • Agent will communicate with the Server
  • This agent needs to verified by server, we will have some security mechanism.
  • Once Agent is authorized, the conversation might look like

    Do i have any work to be done
    

• Bootstrap:
  • Process of installing agent on node is called as Boot-straping
• Convergence:
  • Is the time (periodic) when agent communicates to the server and gets the CM done.
• Configuration Drift:
  • Deviation between desired state and actual state on the node.