The documentation for enabling fastly on Platform.sh is not entirely correct : https://docs.platform.sh/frameworks/ez/fastly.html#set-credentials-on-platformsh

Currently, you also need to set the "HTTPCACHE_PURGE_SERVER" environment variable.. However,  instead of changing the doc, I think we should make it not required to set that environment variable.

I'll also update our fastly installation doc accordingly:

https://doc.ezplatform.com/en/1.13/guide/http_cache/