Getting Started for Airship Developers¶
Airship uses many foundational concepts that should be understood by developers wanting to get started. This documentation attempts to provide a survey of those topics.
Airship is, at its core, intended to be used in a containerized fashion.
Dockerfile resources exist in each of the project repositories that are used by
the build process to generate Docker images. Images are hosted on quay.io
Each main component is responsible for generating one or more images (E.g.: Shipyard produces a Shipyard image and an Airflow image).
When running, nearly every aspect of Airship runs as a container, and Airship (primarily Promenade + Armada) sets up many of the other foundational components as containers, including many Kubernetes components, etcd, Calico, and Ceph.
Each Airship component that runs as a service provides a RESTful API. Some API Conventions exist explaining the basic format of requests and responses and required endpoints that are exposed, such as health check and and design validation.
Security is a consideration from the ground-up for Airship components. Some technologies in this space are TLS and Keystone auth. Airship APIs are protected by RBAC policies implemented with oslo.policy (with some exceptions for basic health checking and listing of API versions). Keystone middleware serves as a layer in the pipeline of service layers for each component, providing lookup of authenticated users, resolving their roles, which are then checked. Access enforcement is within the Airship components, using a decorator for each API that requires limited access.
Airship components are deployed into Kubernetes using Armada, which in turn uses the Tiller component of Helm. Helm charts are used to generate the Kubernetes artifacts (deployments, jobs, configmaps, etc…).
Airship is thoroughly intertwined with Kubernetes:
Airship depends on Kubernetes as the orchestrator of the containers that make up the platform.
Airship sets up a single node Kubernetes instance during the Promenade genesis process, with the necessary configuration to become the seed of a resilient Kubernetes cluster during later stages of Airship.
Airship’s components run as containers inside the Kubernetes cluster.
Airship is targeted to a Linux platform. There are significant elements of Airship that use shell scripts to drive processes.
Further information is available in Code and Project Conventions.
Airship is primarily a combination of Python 3 and shell scripting. There are several Python libraries that are used in common across many components:
Falcon: A service framework providing the API endpoints.
uWSGI: The service container.
oslo_config: Provides per-deployment, configuration file configurability.
oslo_policy: Provides RBAC support for API endpoints (and more).
Requests: A framework for making HTTP requests and receiving responses.
Click: A CLI framework used to provide component-level Command Line Interfaces.
Each component also brings in their own dependencies as needed.
Several of the Airship components require some data persistence. Some data persistence is achieved by utilizing Kubernetes provided mechanisms, and the Keystone software uses a MariaDB instance, but most is accomplished using a containerized PostgreSQL database.
Interaction with PostgreSQL uses the following:
SQLAlchemy: A python library providing most of the needed database functionality.
Alembic: Version management for database schemas and data.
oslo_db: An OpenStack layer providing additional functionality over SQLAlchemy.
Unit and functional tests are used in the gating of changes before merging code. Unit tests utilize combinations of pytest and stestr. Functional tests utilize Gabbi. These tools are not exclusive of others, but are the primary tools being used for unit and functional tests.
Integration testing is orchestrated in the merge gates, and uses various means of testing.