Merge pull request #2500 from mitchellh/docs-amazon-creds

Updated docs on how AWS credentials are resolved

website/source/docs/builders/amazon-chroot.html.markdown

@@ -57,10 +57,7 @@ can be configured for this builder.
 
 ### Required:
 
-* `access_key` (string) - The access key used to communicate with AWS.
+* `access_key` (string) - The access key used to communicate with AWS. [Learn how to set this.](/docs/builders/amazon.html#specifying-amazon-credentials)
-  If not specified, Packer will search the standard [credentials](http://docs.aws.amazon.com/cli/latest/userguide/cli-chap-getting-started.html#cli-config-files) file using environment variable `AWS_PROFILE` as the profile name, will use the `[default]` entry,
-  or will fall back to environment variables `AWS_ACCESS_KEY_ID` or `AWS_ACCESS_KEY`. 
-  Finally, if Packer is running on an EC2 instance it will check the instance metadata for IAM role keys.
 
 * `ami_name` (string) - The name of the resulting AMI that will appear
   when managing AMIs in the AWS console or via APIs. This must be unique.
@@ -68,7 +65,7 @@ can be configured for this builder.
   [configuration templates](/docs/templates/configuration-templates.html) for more info)
 
 * `secret_key` (string) - The secret key used to communicate with AWS.
-  Lookup behavior is as above for `access_key` except the variables are `AWS_SECRET_ACCESS_KEY` or `AWS_SECRET_KEY`.
+  [Learn how to set this.](/docs/builders/amazon.html#specifying-amazon-credentials)
 
 * `source_ami` (string) - The source AMI whose root volume will be copied
   and provisioned on the currently running instance. This must be an

website/source/docs/builders/amazon-ebs.html.markdown

@@ -37,10 +37,7 @@ can be configured for this builder.
 
 ### Required:
 
-* `access_key` (string) - The access key used to communicate with AWS.
+* `access_key` (string) - The access key used to communicate with AWS. [Learn how to set this.](/docs/builders/amazon.html#specifying-amazon-credentials)
-  If not specified, Packer will search the standard [credentials](http://docs.aws.amazon.com/cli/latest/userguide/cli-chap-getting-started.html#cli-config-files) file using environment variable `AWS_PROFILE` as the profile name, will use the `[default]` entry, 
-  or will fall back to environment variables `AWS_ACCESS_KEY_ID` or `AWS_ACCESS_KEY`.
-  Finally, if Packer is running on an EC2 instance it will check the instance metadata for IAM role keys.
 
 * `ami_name` (string) - The name of the resulting AMI that will appear
   when managing AMIs in the AWS console or via APIs. This must be unique.
@@ -53,8 +50,7 @@ can be configured for this builder.
 * `region` (string) - The name of the region, such as "us-east-1", in which
   to launch the EC2 instance to create the AMI.
 
-* `secret_key` (string) - The secret key used to communicate with AWS.
+* `secret_key` (string) - The secret key used to communicate with AWS. [Learn how to set this.](/docs/builders/amazon.html#specifying-amazon-credentials)
-  Lookup behavior is as above for `access_key` except the variables are `AWS_SECRET_ACCESS_KEY` or `AWS_SECRET_KEY`
 
 * `source_ami` (string) - The initial AMI used as a base for the newly
   created machine.

website/source/docs/builders/amazon-instance.html.markdown

@@ -42,10 +42,7 @@ can be configured for this builder.
 
 ### Required:
 
-* `access_key` (string) - The access key used to communicate with AWS.
+* `access_key` (string) - The access key used to communicate with AWS. [Learn how to set this.](/docs/builders/amazon.html#specifying-amazon-credentials)
-  If not specified, Packer will search the standard [credentials](http://docs.aws.amazon.com/cli/latest/userguide/cli-chap-getting-started.html#cli-config-files) file using environment variable `AWS_PROFILE` as the profile name, will use the `[default]` entry,
-  or will fall back to environment variables `AWS_ACCESS_KEY_ID` or `AWS_ACCESS_KEY`.
-  Finally, if Packer is running on an EC2 instance it will check the instance metadata for IAM role keys.
 
 * `account_id` (string) - Your AWS account ID. This is required for bundling
   the AMI. This is _not the same_ as the access key. You can find your
@@ -65,9 +62,7 @@ can be configured for this builder.
 * `s3_bucket` (string) - The name of the S3 bucket to upload the AMI.
   This bucket will be created if it doesn't exist.
 
-* `secret_key` (string) - The secret key used to communicate with AWS.
+* `secret_key` (string) - The secret key used to communicate with AWS. [Learn how to set this.](/docs/builders/amazon.html#specifying-amazon-credentials)
-  Lookup behavior is as above for `access_key` except the variables are `AWS_SECRET_ACCESS_KEY` or `AWS_SECRET_KEY`
-
 
 * `source_ami` (string) - The initial AMI used as a base for the newly
   created machine.

website/source/docs/builders/amazon.html.markdown

@@ -31,6 +31,35 @@ AMI. Packer supports the following builders at the moment:
 [amazon-ebs builder](/docs/builders/amazon-ebs.html). It is
 much easier to use and Amazon generally recommends EBS-backed images nowadays.
 
+<div id="specifying-amazon-credentials">## Specifying Amazon Credentials</div>
+
+When you use any of the amazon builders, you must provide credentials to the API in the form of an access key id and secret. These look like:
+
+    access key id:     AKIAIOSFODNN7EXAMPLE
+    secret access key: wJalrXUtnFEMI/K7MDENG/bPxRfiCYEXAMPLEKEY
+
+If you use other AWS tools you may already have these configured. If so, packer will try to use them, *unless* they are specified in your packer template. Credentials are resolved in the following order:
+
+1. Values hard-coded in the packer template are always authoritative.
+2. *Variables* in the packer template may be resolved from command-line flags or from environment variables. Please read about [User Variables](https://packer.io/docs/templates/user-variables.html) for details.
+3. If no credentials are found, packer falls back to automatic lookup.
+
+### Automatic Lookup
+
+If no AWS credentials are found in a packer template, we proceed on to the following steps:
+
+1. Lookup via environment variables.
+    - First `AWS_ACCESS_KEY_ID`, then `AWS_ACCESS_KEY`
+    - First `AWS_SECRET_ACCESS_KEY`, then `AWS_SECRET_KEY`
+2. Look for [local AWS configuration files](http://docs.aws.amazon.com/cli/latest/userguide/cli-chap-getting-started.html#cli-config-files)
+    - First `~/.aws/credentials`
+    - Next based on `AWS_PROFILE`
+3. Lookup an IAM role for the current EC2 instance (if you're running in EC2)
+
+~> **Subtle details of automatic lookup may change over time.** The most reliable way to specify your configuration is by setting them in template variables (directly or indirectly), or by using the `AWS_ACCESS_KEY_ID` and `AWS_SECRET_ACCESS_KEY` environment variables.
+
+Environment variables provide the best portability, allowing you to run your packer build on your workstation, in Atlas, or on another build server.
+
 ## Using an IAM Instance Profile
 
 If AWS keys are not specified in the template, Packer will consult the [credentials](http://docs.aws.amazon.com/cli/latest/userguide/cli-chap-getting-started.html#cli-config-files) file, try the standard AWS environment variables, and then