This chapter covers
- Application configuration requirements
- Difference between system and app configuration values
- Proper use of property files
- Proper use of environment variables
- Configuration servers
At the start of the preceding chapter, I presented the illustration repeated here in figure 6.1. This diagram shows that although it seems simple that the same inputs to any of a number of application instances would yield the same results, other factors are also influencing those results—namely, the request history, the system environment, and any application configuration. In chapter 5, you studied techniques for eliminating the impact of the first of these by ensuring that any state resulting from a sequence of requests would be stored in a shared backing service, and this allowed the app instances to be stateless.
Figure 6.1. The cloud-native app must ensure consistent outcomes despite differences in contextual influencers such as request history (different app instances have processed a different set of requests) and system environment values (such as IP addresses). Application configuration should be the same across instances but may differ at times.
