You can use IAM Roles for Amazon EC2 to optionally skip credentials configuration all together: if an agent happens to run on an EC2 instance started with an instance profile (IAM role), the tasks can be configured to facilitate those credentials. Of course, the underlying IAM role needs to have a sufficient policy attached to grant the the required permissions for the task at hand.
This feature requires the Amazon EC2 instance running the agent to be started with an EC2 instance profile. There are three different scenarios:
local agents - requires the hosting Bamboo server itself to run on EC2
remote/elastic agents - requires the remote agent to run on EC2
elastic agents - requires the elastic agent to run on EC2
As of release 2.4, you can optionally specify the ARN of another role that the agent's IAM role for EC2 should assume via the EC2 instance profile credentials - this enables various scenarios, notably switching to roles across your own AWS accounts and third-party.AWS accounts (cross-account IAM roles).
Elastic Bamboo only supports configuring elastic images with an instance profile as of Bamboo 5.6.