Software that takes advantage of what the cloud has to offer must take on a new shape. Applications deployed to the cloud need to show resilience in the face of VMs or server instances going down or not behaving as expected. Applications deployed to cloud infrastructures also tend to need to scale temporarily to keep costs reasonable and automatic based on patterns of usage. Learning faster than your competition is of utmost importance to many who deploy software into a cloud therefore deploying updates on a continuous basis becomes critical. There is an approach to developing and deploying applications into the cloud, The Twelve-Factor App.
The Twelve Factors of this approach are:I. Codebase – One codebase tracked in revision control, many deploys
II. Dependencies – Explicitly declare and isolate dependencies
III. Config – Store config in the environment
IV. Backing Services – Treat backing services as attached resources
V. Build, release, run – Strictly separate build and run stages
VI. Processes – Execute the app as one or more stateless processes
VII. Port binding – Export services via port binding
VIII. Concurrency – Scale out via the process model
IX. Disposability – Maximize robustness with fast startup and graceful shutdown
X. Dev/prod parity – Keep development, staging, and production as similar as possible
XI. Logs – Treat logs as event streams
XII. Admin processes – Run admin/management tasks as one-off processes
These factors tend to drive highly cohesive applications and services that also exhibit low coupling with their dependencies. Each application or service should be in a single repository that can be built and deployed on its own. Rather than branching or forking to create multiple deployable versions of the application, we should externalize configuration so that the maintenance costs are not exponentially growing to support all versions of the application. These applications should also have understandable boundaries and implement a single concept or responsibility to increase their disposability. Creating stateless applications and services enables horizontal scaling and redundancy across multiple nodes in a cloud. Deploying multiple instances of an application or service results in multiple ports that can load balanced and registered for use by others.
Some of these factors are no brainers for many experienced developers and some are not as easy to implement due to access restrictions to configuration management and flexible operating platforms. For those of us fortunate enough to use “real” cloud infrastructure, today’s cloud vendors are starting to provide services that enable Twelve-Factor Apps. The Cloud Foundry Foundation officially launched this week as part of the Linux Foundation Collaborative Projects. Cloud Foundry is the most robust and mature open source Platform-as-a-Service (PaaS) offering in the market. With Cloud Foundry it has become much easier to apply The Twelve-Factor App approach to applications and services. Buildpacks enable the use of polyglot software development across applications and services yet still deploy into a single PaaS. Software can be deployed using a single command to a PaaS: `cf push <appname>`. Zero scheduled downtime deployments can be performed using a Blue/Green Deployment approach, described well by Martin Fowler here, that keeps existing versions of the software (Blue) up while deploying and testing new versions (Green) that can run alongside or replace the old version (Blue) when validated as ready. And binding to dependent services, such as DB clusters and message queues, can be simplified to create a named service deployment with `cf create-service mongodb cluster my-mongo-cluster` and then binding it to your application with `cf bind-service my-app-1 my-mongo-cluster`. It is incredible how Cloud Foundry can make creating and continuously delivering a Twelve-Factor App orders of magnitude easier than constructing and managing your own infrastructure or in an Infrastructure-as-a-Service (IaaS) platform. When you need to optimize the deployment environment you can always take a single application or service and adjust it to deploy into your own data center or an IaaS platform but since they take The Twelve-Factor Approach you don’t have to do it for all of your applications and services.
I hope this article provides awareness around The Twelve-Factor App approach and how a PaaS, such as Cloud Foundry, can enable effective use of the approach. I recommend clicking the links provided in this article to read more details about the approach and how to take advantage of what Cloud Foundry has to offer. It is imminent that in the next few years that Twelve-Factor Apps will become more the norm in software development shops and PaaS will be a common deployment platform. Take the time to read and experiment with Cloud Foundry to get a leg up on this imminent acceleration of PaaS and The Twelve-Factor Apps approach.