» Amazon AMI Builder

Packer is able to create Amazon AMIs. To achieve this, Packer comes with multiple builders depending on the strategy you want to use to build the AMI. Packer supports the following builders at the moment:

  • amazon-ebs - Create EBS-backed AMIs by launching a source AMI and re-packaging it into a new AMI after provisioning. If in doubt, use this builder, which is the easiest to get started with.

  • amazon-instance - Create instance-store AMIs by launching and provisioning a source instance, then rebundling it and uploading it to S3.

  • amazon-chroot - Create EBS-backed AMIs from an existing EC2 instance by mounting the root device and using a Chroot environment to provision that device. This is an advanced builder and should not be used by newcomers. However, it is also the fastest way to build an EBS-backed AMI since no new EC2 instance needs to be launched.

  • amazon-ebssurrogate - Create EBS -backed AMIs from scratch. Works similarly to the chroot builder but does not require running in AWS. This is an advanced builder and should not be used by newcomers.

» Amazon EBS Volume Builder

Packer is able to create Amazon EBS Volumes which are preinitialized with a filesystem and data.

  • amazon-ebsvolume - Create EBS volumes by launching a source AMI with block devices mapped. Provision the instance, then destroy it, retaining the EBS volumes.

» Authentication

The AWS provider offers a flexible means of providing credentials for authentication. The following methods are supported, in this order, and explained below:

  • Static credentials
  • Environment variables
  • Shared credentials file
  • EC2 Role

» Static Credentials

Static credentials can be provided in the form of an access key id and secret. These look like:

{
    "access_key": "AKIAIOSFODNN7EXAMPLE",
    "secret_key": "wJalrXUtnFEMI/K7MDENG/bPxRfiCYEXAMPLEKEY",
    "region": "us-east-1",
    "type": "amazon-ebs"
}

» Environment variables

You can provide your credentials via the AWS_ACCESS_KEY_ID and AWS_SECRET_ACCESS_KEY, environment variables, representing your AWS Access Key and AWS Secret Key, respectively. Note that setting your AWS credentials using either these environment variables will override the use of AWS_SHARED_CREDENTIALS_FILE and AWS_PROFILE. The AWS_DEFAULT_REGION and AWS_SESSION_TOKEN environment variables are also used, if applicable:

Usage:

$ export AWS_ACCESS_KEY_ID="anaccesskey"
$ export AWS_SECRET_ACCESS_KEY="asecretkey"
$ export AWS_DEFAULT_REGION="us-west-2"
$ packer build packer.json

» Shared Credentials file

You can use an AWS credentials file to specify your credentials. The default location is $HOME/.aws/credentials on Linux and OS X, or "%USERPROFILE%.aws\credentials" for Windows users. If we fail to detect credentials inline, or in the environment, Packer will check this location. You can optionally specify a different location in the configuration by setting the environment with the AWS_SHARED_CREDENTIALS_FILE variable.

The format for the credentials file is like so

[default]
aws_access_key_id=<your access key id>
aws_secret_access_key=<your secret access key>

You may also configure the profile to use by setting the profile configuration option, or setting the AWS_PROFILE environment variable:

{
    "profile": "customprofile",
    "region": "us-east-1",
    "type": "amazon-ebs"
}

» IAM Task or Instance Role

Finally, Packer will use credentials provided by the task's or instance's IAM role, if it has one.

This is a preferred approach over any other when running in EC2 as you can avoid hard coding credentials. Instead these are leased on-the-fly by Packer, which reduces the chance of leakage.

The following policy document provides the minimal set permissions necessary for Packer to work:

{
  "Version": "2012-10-17",
  "Statement": [{
      "Effect": "Allow",
      "Action" : [
        "ec2:AttachVolume",
        "ec2:AuthorizeSecurityGroupIngress",
        "ec2:CopyImage",
        "ec2:CreateImage",
        "ec2:CreateKeypair",
        "ec2:CreateSecurityGroup",
        "ec2:CreateSnapshot",
        "ec2:CreateTags",
        "ec2:CreateVolume",
        "ec2:DeleteKeyPair",
        "ec2:DeleteSecurityGroup",
        "ec2:DeleteSnapshot",
        "ec2:DeleteVolume",
        "ec2:DeregisterImage",
        "ec2:DescribeImageAttribute",
        "ec2:DescribeImages",
        "ec2:DescribeInstances",
        "ec2:DescribeRegions",
        "ec2:DescribeSecurityGroups",
        "ec2:DescribeSnapshots",
        "ec2:DescribeSubnets",
        "ec2:DescribeTags",
        "ec2:DescribeVolumes",
        "ec2:DetachVolume",
        "ec2:GetPasswordData",
        "ec2:ModifyImageAttribute",
        "ec2:ModifyInstanceAttribute",
        "ec2:ModifySnapshotAttribute",
        "ec2:RegisterImage",
        "ec2:RunInstances",
        "ec2:StopInstances",
        "ec2:TerminateInstances"
      ],
      "Resource" : "*"
  }]
}

Note that if you'd like to create a spot instance, you must also add:

ec2:RequestSpotInstances,
ec2:CancelSpotInstanceRequests,
ec2:DescribeSpotInstanceRequests

If you have the spot_price parameter set to auto, you must also add:

ec2:DescribeSpotPriceHistory

» Troubleshooting

» Attaching IAM Policies to Roles

IAM policies can be associated with users or roles. If you use packer with IAM roles, you may encounter an error like this one:

==> amazon-ebs: Error launching source instance: You are not authorized to perform this operation.

You can read more about why this happens on the Amazon Security Blog. The example policy below may help packer work with IAM roles. Note that this example provides more than the minimal set of permissions needed for packer to work, but specifics will depend on your use-case.

{
    "Sid": "PackerIAMPassRole",
    "Effect": "Allow",
    "Action": "iam:PassRole",
    "Resource": [
        "*"
    ]
}

» Checking that system time is current

Amazon uses the current time as part of the request signing process. If your system clock is too skewed from the current time, your requests might fail. If that's the case, you might see an error like this:

==> amazon-ebs: Error querying AMI: AuthFailure: AWS was not able to validate the provided access credentials

If you suspect your system's date is wrong, you can compare it against http://www.time.gov/. On Linux/OS X, you can run the date command to get the current time. If you're on Linux, you can try setting the time with ntp by running sudo ntpd -q.

» exceeded wait attempts while waiting for tasks to complete

We use the AWS SDK's built-in waiters to wait for longer-running tasks to complete. These waiters have default delays between queries and maximum number of queries that don't always work for our users.

If you find that you are being rate-limited or have exceeded your max wait attempts, you can override the defaults by setting the following packer environment variables (note that these will apply to all aws tasks that we have to wait for):

AWS_MAX_ATTEMPTS - This is how many times to re-send a status update request. Excepting tasks that we know can take an extremely long time, this defaults to 40tries.

AWS_POLL_DELAY_SECONDS - How many seconds to wait in between status update requests. Generally defaults to 2 or 5 seconds, depending on the task.