Deis is a lightweight application platform that deploys and scales Twelve-Factor apps as Docker containers across a cluster of Kubernetes minions.
The Twelve-Factor App is a methodology for building modern applications that can be scaled across a distributed system.
We consider it an invaluable synthesis of much experience with software-as-a-service apps in the wild, especially on the Heroku platform.
Workflow is designed to run applications that adhere to Twelve-Factor App methodology and best practices.
[Kubernetes][] is an open-source cluster manager developed by Google and donated to the [Cloud Native Compute Foundation][cncf]. Kubernetes manages all the activity on your cluster. Including converging to a desired state, providing critical functions like stable service addresses, health monitoring, service discovery and DNS resolution.
Workflow builds upon Kubernetes abstractions like Services, Replication Controllers and Pods to provide a developer-friendly UX, source to image, log aggregation, etc.
Workflow is shipped as a Kubernetes-native application, installable via [Helm][helm]. So operators familiar with Kubernetes will feel right at home running Workflow.
For a detailed overview of Workflow components, see our [component][] break down.
Docker is an open source project to build, ship and run any application as a lightweight, portable, self-sufficient container.
Workflow uses Docker Images and the Docker Engine (via Kubernetes) to package and run your application respectively.
If you have not yet converted your application to containers, Workflow provides
a simple and straightforward "source to Docker image" capability. Supporting
multiple language runtimes via community buildpacks, building your application
in a container can be as easy as git push deis master.
Deis is designed around the concept of an application, or app. Applications live on a cluster where they use Containers to service requests.
Developers use applications to push code, change configuration, scale processes, view logs, run admin commands and much more.
The builder processes incoming git push requests and builds applications
inside ephemeral Docker containers, resulting in a new Docker image.
During the release stage, a build is combined with config to create a new numbered release. This release is then pushed to a Docker registry for later execution. The release stage is triggered any time a new build is created or config is changed, making it easy to rollback code and configuration changes.
The run stage dispatches containers to a scheduler and updates the router accordingly. The scheduler is in control of placing containers on hosts and balancing them evenly across the cluster. Containers are published to the router once they are healthy. Old containers are only collected after the new containers are live and serving traffic -- providing zero-downtime deploys.
Deis treats databases, caches, storage, messaging systems, and other backing services as attached resources, in keeping with Twelve-Factor best practices.
Applications are attached to backing services using environment variables. Because applications are decoupled from backing services, apps are free to scale up independently, to swap services provided by other apps, or to switch to external or third-party vendor services.