3-tier architecture
More variations
Application server
For the web, the middle tier is a web server.
Most often, the web server invokes code in some other language:
- .cgi: Code in another process via
the cgi interface, (obsolete).
- PHP
- Other languages via Apache modules E.g., python
Alternative approach:
- Instead of a web server with a language grafted in, some applications are built
with an application server.
- An application server is a general-purpose server, that can also
work as a web server, i.e., support HTTP.
The most common application servers are written in Java:
- Weblogic: Goes back to the 90s, acquired by Oracle.
- Websphere: IBM.
- Jetty: Open source.
Outside the scope of this course.
But relevant because so much database access is done from application servers.
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