Packer

Testing HashiCorp's Packer - a tool for building Golden Images.

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Use cases

1. Create golden images across platforms and environments
2. Automate patching for workloads
3. Creating immutable infrastructure

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Starting a Packer build:

# First prettify packer files
packer fmt Jenkins-AMI/

# Validate that the syntax is correct 
packer validate Jenkins-AMI/

# Start the build 
packer build Jenkins-AMI/

# Build all templates in a directory
packer build <directory>

# Convert old JSON format packer files to new HCL format
packer hcl2_upgrade <file>

Building Consul AMI

# Select whether it's a client or server machine 
packer build -var is_server=true consul/

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Builders

• Responsible for creating machines and generating images from them for various platforms
• One or more builder blocks can be specified in a template
• Each builder block can specify one or more source blocks

Variables

Contextual variables

• Metadata about the build that was executed
• All special build variables are stored in the build variable

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Provisioners

File

• Used for copying files from local machine to the machine being built by Packer
• Common pattern is to copy files to /tmp directory in the Packer machine as it can be freely modified

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• Some issues were faced as a result of running as ec2-user instead of root

• To become root execute_command is used with the provisioner

Becoming root with shell provisioner

  // Configure AMI as NAT Instance
  provisioner "shell" {
    /* 
    - execute_command changes the default user from ec2-user to root
    - sysctl commands aren't allowed to be run under the default ec2-user as they modify the kernel 
    */
    execute_command = "echo 'packer' | sudo -S env {{ .Vars }} {{ .Path }}"
    inline = [
      # https://www.kabisa.nl/tech/cost-saving-with-nat-instances/
      "sysctl -w net.ipv4.ip_forward=1 >> /etc/sysctl.conf",
      "/sbin/iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE",
      "iptables-save > /etc/iptables.conf",
      "echo 'iptables-restore < /etc/iptables.conf' >> /etc/rc.local"
    ]
  }

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Resources

1. UDEMY - Building Automated Machine Images with HashiCorp Packer