Backing Services
- A backing service is any service the app consumes over the network as part of its normal operation. Examples include datastores (such as MySQL or CouchDB), messaging/queueing systems (such as RabbitMQ or Beanstalkd), SMTP services for outbound email (such as Postfix), and caching systems (such as Memcached).
- Your code will talk to many services, like a database, a cache, an email service, a queueing system, etc. These should all be referenced by a simple endpoint (URL) and maybe a username and password. They might be running on the same machine, or they might be on a different host, in a different datacenter, or managed by a cloud SaaS company. The point is, your code shouldn’t know the difference.
- This is another case where defining your dependencies cleanly keeps your system flexible and each part is abstracted from the complexities of the others…a core tenet of good architecture.
- The code for a twelve-factor app makes no distinction between local and third party services. To the app, both are attached resources, accessed via a URL or other locator/credentials stored in the config. A deploy of the twelve-factor app should be able to swap out a local MySQL database with one managed by a third party (such as Amazon RDS) without any changes to the app’s code. Likewise, a local SMTP server could be swapped with a third-party SMTP service (such as Postmark) without code changes. In both cases, only the resource handle in the config needs to change.
Importance: High