packer-cn/website/source/intro/getting-started/build-image.html.markdown

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Build an Image

With Packer installed, let's just dive right into it and build our first image. Our first image will be an Amazon EC2 AMI with Redis pre-installed. This is just an example. Packer can create images for many platforms with anything pre-installed.

If you don't have an AWS account, create one now. For the example, we'll use a "t1.micro" instance to build our image, which qualifies under the AWS free-tier, meaning it will be free. If you already have an AWS account, you may be charged some amount of money, but it shouldn't be more than a few cents.

Note that if you're not using an account that qualifies under the AWS free-tier, you may be charged to run these examples. The charge should only be a few cents, but we're not responsible if it ends up being more.

Packer can build images for many platforms other than AWS, but AWS requires no additional software installed on your computer and their free-tier makes it free to use for most people. This is why we chose to use AWS for the example. If you're uncomfortable setting up an AWS account, feel free to follow along as the basic principles apply to the other platforms as well.

The Template

The configuration file used to define what image we want built and how is called a template in Packer terminology. The format of a template is simple JSON. JSON struck the best balance between human-editable and machine-editable, allowing both hand-made templates as well as machine generated templates to easily be made.

We'll start by creating the entire template, then we'll go over each section briefly. Create a file example.json and fill it with the following contents:

{
  "variables": {
    "aws_access_key": "",
    "aws_secret_key": ""
  },
  "builders": [{
    "type": "amazon-ebs",
    "access_key": "{{user `aws_access_key`}}",
    "secret_key": "{{user `aws_secret_key`}}",
    "region": "us-east-1",
    "source_ami": "ami-de0d9eb7",
    "instance_type": "t1.micro",
    "ssh_username": "ubuntu",
    "ami_name": "packer-example {{timestamp}}"
  }]
}

When building, you'll pass in the aws_access_key and aws_secret_key as a user variable, keeping your secret keys out of the template. You can create security credentials on this page. An example IAM policy document can be found in the Amazon EC2 builder docs.

This is a basic template that is ready-to-go. It should be immediately recognizable as a normal, basic JSON object. Within the object, the builders section contains an array of JSON objects configuring a specific builder. A builder is a component of Packer that is responsible for creating a machine and turning that machine into an image.

In this case, we're only configuring a single builder of type amazon-ebs. This is the Amazon EC2 AMI builder that ships with Packer. This builder builds an EBS-backed AMI by launching a source AMI, provisioning on top of that, and re-packaging it into a new AMI.

The additional keys within the object are configuration for this builder, specifying things such as access keys, the source AMI to build from, and more. The exact set of configuration variables available for a builder are specific to each builder and can be found within the documentation.

Before we take this template and build an image from it, let's validate the template by running packer validate example.json. This command checks the syntax as well as the configuration values to verify they look valid. The output should look similar to below, because the template should be valid. If there are any errors, this command will tell you.

$ packer validate example.json
Template validated successfully.

Next, let's build the image from this template.

An astute reader may notice that we said earlier we'd be building an image with Redis pre-installed, and yet the template we made doesn't reference Redis anywhere. In fact, this part of the documentation will only cover making a first basic, non-provisioned image. The next section on provisioning will cover installing Redis.

Your First Image

With a properly validated template. It is time to build your first image. This is done by calling packer build with the template file. The output should look similar to below. Note that this process typically takes a few minutes.

$ packer build \
    -var 'aws_access_key=YOUR ACCESS KEY' \
    -var 'aws_secret_key=YOUR SECRET KEY' \
    example.json
==> amazon-ebs: amazon-ebs output will be in this color.

==> amazon-ebs: Creating temporary keypair for this instance...
==> amazon-ebs: Creating temporary security group for this instance...
==> amazon-ebs: Authorizing SSH access on the temporary security group...
==> amazon-ebs: Launching a source AWS instance...
==> amazon-ebs: Waiting for instance to become ready...
==> amazon-ebs: Connecting to the instance via SSH...
==> amazon-ebs: Stopping the source instance...
==> amazon-ebs: Waiting for the instance to stop...
==> amazon-ebs: Creating the AMI: packer-example 1371856345
==> amazon-ebs: AMI: ami-19601070
==> amazon-ebs: Waiting for AMI to become ready...
==> amazon-ebs: Terminating the source AWS instance...
==> amazon-ebs: Deleting temporary security group...
==> amazon-ebs: Deleting temporary keypair...
==> amazon-ebs: Build finished.

==> Builds finished. The artifacts of successful builds are:
--> amazon-ebs: AMIs were created:

us-east-1: ami-19601070

At the end of running packer build, Packer outputs the artifacts that were created as part of the build. Artifacts are the results of a build, and typically represent an ID (such as in the case of an AMI) or a set of files (such as for a VMware virtual machine). In this example, we only have a single artifact: the AMI in us-east-1 that was created.

This AMI is ready to use. If you wanted you can go and launch this AMI right now and it would work great.

Note: Your AMI ID will surely be different than the one above. If you try to launch the one in the example output above, you will get an error. If you want to try to launch your AMI, get the ID from the Packer output.

Managing the Image

Packer only builds images. It does not attempt to manage them in any way. After they're built, it is up to you to launch or destroy them as you see fit. As a result of this, after running the above example, your AWS account now has an AMI associated with it.

AMIs are stored in S3 by Amazon, so unless you want to be charged about $0.01 per month, you'll probably want to remove it. Remove the AMI by first deregistering it on the AWS AMI management page. Next, delete the associated snapshot on the AWS snapshot management page.

Congratulations! You've just built your first image with Packer. Although the image was pretty useless in this case (nothing was changed about it), this page should've given you a general idea of how Packer works, what templates are, and how to validate and build templates into machine images.