DevOps Classroom Series – Packer – 04/Jan/2020

Provisioning in Packer

• Shell Provisioning:
  • Executes Linux commands or shell script(s) once the VM is created.
• Ansible Provisioning:
• Chef Provisioning

Applying Shell Provisioner with script

• Create a file called as installtomcat.sh in the same directory as aws.json
• Add the following content

#!/bin/bash
sudo apt-get update
sleep 10
sudo apt-get install openjdk-8-jdk -y
sleep 10
sudo apt-get install tomcat8 -y
sleep 10

• Change the shell provisioner from inline to script as shown below

{
    "builders": [
        {
            "type": "amazon-ebs",
            "ami_name": "tomcatfrompacker",
            "ami_description": "tomcat from packer",
            "access_key": "AKIA3TXJQGAJFDVFHD7C",
            "secret_key": "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",
            "region": "us-west-2",
            "instance_type": "t2.micro",
            "source_ami": "ami-06d51e91cea0dac8d",
            "ssh_username": "ubuntu"

    }],
    "provisioners": [
        {
            "type": "shell",
            "script": "./installtomcat.sh"
        }
    ]
}

• Note: Refer Here for complete info on shell provisioner.

Variables in Packer

• Variables in Packer give the flexibility of changing values used in builders/provisioners
• For variables a section called as varaibles is available in Packer.
• Variables defined in the Packer Template are called as user variables
• Basic Structure of packer template with variables is as shown below

{
    "variables": {

    },
    "builders": [],
    "provisioners": []
}

• To define a variables simple add a key pair/name pair to json

{
    "variables": {
        "myvar": "hello"
    },
    "builders": [],
    "provisioners": []
}

• To use myvar variable in bulders or provisioners section use the following syntax

"{{user `myvar`}}"

• To the above packer template if we add variables for access, secret keys and region, source ami the template looks as follows

{
    "variables": {
        "aws_access_key": "",
        "aws_secret_key": "",
        "source_image_id": "ami-06d51e91cea0dac8d",
        "image_region": "us-west-2"

    },
    "builders": [
        {
            "type": "amazon-ebs",
            "ami_name": "tomcatfrompacker",
            "ami_description": "tomcat from packer",
            "access_key": "{{user `aws_access_key`}}",
            "secret_key": "{{user `aws_secret_key`}}",
            "region": "{{user `image_region`}}",
            "instance_type": "t2.micro",
            "source_ami": "{{user `source_image_id`}}",
            "ssh_username": "ubuntu"

    }],
    "provisioners": [
        {
            "type": "shell",
            "script": "./installtomcat.sh"
        }
    ]
}

• To validate the template use the -var argument

packer validate -var 'aws_access_key=<accesskey>' -var 'aws_secret_key=<secretkey>' .\aws.json

• To build the image from template

packer build -var 'aws_access_key=<accesskey>' -var 'aws_secret_key=<secretkey>' .\aws.json

• If you are using many variables -var-file option is available. Create a Json file with all variable names and values and use that file rather than individual -var parameters

packer validate -var-file myvariables.json ./aws.json

packer build -var-file myvariables.json ./aws.json