The data tier
In our case, the database is implemented with the PostgreSQL database system. PostgreSQL is a relational database management system. While arguably not as common as MySQL installations, larger enterprises might prefer Oracle databases. PostgreSQL is, in any case, a robust system, and our example organization has chosen PostgreSQL for this reason.
From a DevOps point of view, the three-tier pattern looks compelling, at least superficially. It should be possible to deploy changes to each of the three layers separately, which would make it simple to propagate small changes through the servers.
Tip
In practice, though, the data tier and logic tier are often tightly coupled. The same might also be true for the presentation tier and logic tier. To avoid this, care must be taken to keep the interfaces between the tiers lean. Using well-known patterns isn't necessarily a panacea. If we don't take care while designing our system, we can still wind up with an undesirable monolithic system...
