http://e26whn2524322mkxb3cbyk27ev2ihhq2biz35hty7gzgsyrwrygq27yd.onion/posts/documentation/linux/745-allowing-your-internal-search-engine-to-index-gitlab-issues-commits-and-wiki-pages.html
You can have a bunch of read-only viewers hit GILS pages without needing to worry too much about Gitlab's RAM noshing ways. Each page links out to it's Gitlab equivalent, so users that do need to complete actions can trivially do so. Almost more importantly that being able to index your issues though, is being able to index your wiki pages.