Although ESI is not supported by OLS, the following description may encourage you to use LiteSpeed Enterprise instead of OLS. OLS and LSWS are similar if not identical in many ways. In terms of performance, there are certainly few disadvantages to OLS. This also applies if you use a CMS where private content does not play a role. This is especially true when displaying, for example, the login status and especially in an online shop that displays the current shopping cart everywhere on one page. You can overcome the deficit of a page cache using client side scripting, but not every CMS supports this. In such a case, you need ESI because it is only possible with ESI to assign different cache rules to certain content areas. To make it more understandable, LScache and thus a Page Cache creates 1 cache copy of 1 URL. With ESI you can punch an unlimited number of holes in the page cache and each hole gets its own cache rules regardless of the overall cache rules. So if a page has a public cache, then an ESI hole can have a private cache with a separate TTL of the cache. The main advantage of ESI is that every ESI hole does not generate a new HTTP request, as is essential with client side scripting, for example. ESI is server based and therefore works independently of client-dependent functions.
ESI is available both inline and include. The result is the same, but the respective CMS requires either one or the other ESI version. To illustrate what ESI is good for, the two examples should help. If something is unclear, just ask.
esi:inline:
https://www.dev.cachecrawler.com/esi/
esi:include
https://www.dev.cachecrawler.com/esi/include.php
ESI is available both inline and include. The result is the same, but the respective CMS requires either one or the other ESI version. To illustrate what ESI is good for, the two examples should help. If something is unclear, just ask.
esi:inline:
https://www.dev.cachecrawler.com/esi/
esi:include
https://www.dev.cachecrawler.com/esi/include.php