Application of twelve factors (4)

IV The back-end service

Treat back-end services as pluggable resources

A back-end service is any service consumed when an application is running normally on the network . Include database （ Such as MySQL or CouchDB）, news / Queue system （ Such as RabbitMQ or Beantalkd）, Email SMTP service （ Such as Postfix）, Cache system （ Such as Memcached）.

Database, a back-end service, is traditionally managed by the same system administrator as application runtime deployment . In addition to these locally managed services , Applications also have services managed by third parties . Such as SMTP service （Postmark）, Measurement data collection services （ Such as New Relic or Loggly）, Binary storage service （ Such as Amazon S3）, even to the extent that API Access service （Twitter,GoogleMap, or Last.fm）.

12 The code of the factor application makes no difference between these local and third-party services . Application end , Are pluggable resources , adopt URL Or other configured positioning / Authentication services . One copy 12 The deployment of factor application can be implemented locally without any code modification MySQL Replace the database with a third-party service （ Such as Amazon RDS）. alike , Local SMTP Services can be replaced by third parties SMTP service （ Such as Postmark） Without changing the code . Between the two case, Only the configuration file for processing resources needs to be changed .

Every back-end service is a resource . Such as MySQL It's a resource , Two MySQL database （ At the application layer sharding） Two independent resources .12 Factor applications see these databases as pluggable resources , It is loosely coupled when deployed .

Resources can be plugged in and out at deployment as desired . Such as , If the application database fails due to hardware problems , Application administrators can quickly recover from a recent backup . The current production library can be unloaded , The new database is mounted – No code changes are required .

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