I duunno exactly what Craigslist is running on today, but some slides from 2012[1] include items like running MongoDB over "3 shards across 3 node replica sets" with "duplicate config in 2nd data center"; a "sharded multi-node" redis cluster; multiple "vertically partitioned" MySQL clusters; the actual application stack on top of that being mod_perl on Apache, and it was all operated by a 'small but growing' dedicated team.

It might or might not be notable that the growth of that tech team included, one year later, hiring Larry Wall[2].

Given that, I'm not sure how to apply 'if Craigslist doesn't need it, I probably don't' as a general principle....

[1] https://www.slideshare.net/jzawodn/living-with-sql-and-nosql... [2] http://blog.craigslist.org/2013/10/15/artist-formerly-known/

I see language as a personal choice, and while I wouldn't run perl today (I'm partial to Python, myself), I think there stack is fairly simple - tried & true language (however quirky it may be), no virtualization, simple metal hardware stack, and yet they serve an incredible number of users. In that sense, I'm sure hiring Larry was a no-brainer.

They are no FB, but they're bigger than almost anything else on the web [0]. I doubt most people will build anything bigger in their careers. I certainly won't.

A huge caveat might be app features. Clearly running something like travelocity could require more pieces, and something like a BI app in a fortune 100 company would have many more connectors to data sources. But in general, they've done pretty well using only newer versions of what worked way back in 1999, and to me, that's just incredible.

[0] - https://www.semrush.com/blog/most-visited-websites/