Please confirm whether SSI or ESI is supported on AEMaaCS.
As mod_include is not listed on 1, the tutorial in 2 may not be applicable for AEMaaCS.
Currently, ESI is not supported with the OOTB CDN (Fastly) on AEM as a Cloud Service. This feature would require a way to disable
gzip compression on the parent resources for ESI to work. Some of the challenges can be found in 1 for your information.
Regarding SSI, the Apache module
'mod_include' 2 is loaded by default and can be used for SSI using SDI (Sling Dynamic Includes), which works on both local SDK and AEM CS. Please see the community article at 3 for more information.