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Web Servers

11. What are Server Side Includes (SSI)?

When you need to patch a small section of on-the-fly content into an otherwise static page, CGI is a heavy-handed solution. An alternative almost as widely supported as CGI is server-side includes (SSI), which allow you to "include" dynamic content into web pages using special HTML tags.

SSI tags have the form:

<!--#command argument="value" -->

Details of the command set and syntax are documented online in the original NCSA tutorial. Apacheweek also maintains a good how-to article.

Performance impact. Unlike standard HTML, which is parsed and rendered by a web browser after the page has been served, SSI tags are parsed on the server (hence, "server-side includes"). Finding and parsing these tags can slow server response, so webmasters typically specify which files contain SSI tags by using a unique file extension, such as .shtml or .shtm. This is done by adding a line to the MIME content type definition:

AddType text/x-server-parsed-html .shtml

Only files with this MIME type will be parsed by the server.

Note: Like CGI, SSI is a first-generation Web technology and suffers many of the same drawbacks. It is best used to implement simple page dynamics on Unix servers. Sites built on Microsoft Internet Information Server (IIS) should consider using its bundled scripting technology, ASP.