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Components Architecture

There are two major components in pipelines - the orchestrator and the executor. The orchestrator determines the jobs to be executed and the executor actually executes the jobs and makes any necessary updates in AWS.

Orchestrator​

The orchestrator identifies each infrastructure change in a pull request or git commit, classifies the type of infrastructure change it is (e.g. AccountsAdded, ModuleChanged, EnvCommonChanged), and determines the right pipelines actions (e.g., terragrunt plan, apply, or destroy) to run based on that infrastructure change.

Executor​

The executor takes a pipeline action and infra change as input then performs the action on the infra change. In some cases, like responding to AccountsAdded events on merge, the executor will create a subsequent pull request in the infrastructure-live-root repository with additional IaC code to baseline the account(s) that were just added.

Execution Flow​

Pipelines starts with an event in GitHub - a pull request being created, updated, or re-opened, and a PR being merged to main (or any other push to main). From there, the orchestrator determines the infra-change set and appropriate action to run for each infra-change. For each change in the infra-change set, the executor runs the appropriate action. The executor then logs the results of the action back in GitHub on the pull request that initiated the flow.

Trust Boundaries​

Vital to the architecture of Pipelines is understanding of the trust model inherent to the system. Pipelines is designed to be run in a CI/CD system, which means that it has privileged access to your AWS accounts.

One principle to keep in mind is that anyone with trust to edit code on the main branch of your repositories is trusted to make the corresponding changes in your AWS accounts. This is why we recommend that you follow the Repository Access guidelines to ensure that only the right people have the right access to your repositories.

In addition, each AWS IAM role provisioned as part of DevOps Foundations only trusts a single repository (and for apply roles, only a single branch). If you find that you are expanding the permissions of a given role too wide, you should consider creating a new role that has more granular permissions for the specific use-case. Utilize the infrastructure-live-access-control repository to support that need.