etcd is adistributedkey-valuestore, used asshared clusterconfigurationbackend. Itautomaticallyelects a masterserver, allowsdynamic configdata withoptional TTLs,provides a JSONAPI over HTTPwith TLS andlong polling,uses the Raftprotocol fordistribution.It's thebasis forCoreOS,integrates withfleet/systemd,and thus alsoprovidesservicediscovery.
Varnish Cacheis a webapplicationacceleratoralso known as acaching HTTPreverse proxy.You install itin front of anyserver thatspeaks HTTP andconfigure it tocache thecontents.Varnish Cacheis really,really fast. Ittypicallyspeeds updelivery with afactor of 300 -1000x,depending onyourarchitecture.
EmbedthisAppweb is afast, littleembedded Webserver. It isunmatched inefficiency andserves pages atnative speed,using anevent-driven,non-blockingcore to servemultiplerequests usingminimalresources. Ithas integratedcaching and theESP"C"Web framework.Withoutcompromisingperformance, ithas extensivesecuritycontrols and arigoroussecuritysandbox thathelps protectthe server andmitigatedenial-of-serviceattacks. It isone of the mostwidely deployedembedded Webservers