In travel tech search engines are a different thing from common IT. In IT you store all the data inside your database, and then you need to create some index. For the aggregators in travel tech you can only fetch available hotels with prices through API in real time.

A simple solution can start as a IO bound service with classic key value storage like redis. Then you try to make a good HA multi master redis, but fail and switch to Aerospike. Later suppliers ask you to lower search requests to API, and you come with custom load balancing based on rendezvous hashing to group them. Some suppliers ask to have a white IP for ACL, but your bare-metal infrastructure does not have a NAT gateway as AWS and you need to fine-tune the HAProxy by hand.

So we will see how we evolutionary come to these and other decisions.