Name that architecture

A full system diagram, four options. Spot the parts that give it away, pick the system, then see which details decided it.

Each diagram is a typical interview design for a service like the one named, not the company's real architecture.

UserLoad balancerLink serviceanswers 302 redirectsID generator7-char base62 codesCachehot codesKey-value storecode → long URLClick queueClick counterclicks per code

Which kind of system is this?

CreatorUpload serviceresumable, in chunksRaw video storagefiles up to many GBTranscoding queueTranscoders240p … 4KVideo storageevery resolutionCDNadaptive bitrateViewerAPIMetadata DBtitles, channelsSearch indextitles, captions

Which kind of system is this?

Phone appprefetches next 3 clipsUpload serviceclips up to 60 sTranscodersVideo storageCDNFeed serviceFor You feedRecommendation serviceranks candidatesFeature storeuser + clip featuresEvent streamwatch time, swipes, likesModel trainingdeploys the ranking model

Which kind of system is this?

Streamerstreaming softwareIngest serversRTMP stream inLive transcodersreal time, several bitratesEdge / CDN2–6 s HLS segmentsViewersthousands per channelRecorderoptional replayReplay storageChat gatewayWebSocketPub/subone topic per channel

Which kind of system is this?

Appcan download for offlineAPI gatewayCatalogue servicerights per countryMetadata DBtracks, albums, artistsAudio storage3–10 MB per track, 3bitratesCDNLicence serviceDRM keys for offlinePlaylist servicePlay eventsRoyalty countingplays per rights holder

Which kind of system is this?

UserLoad balancerPost servicePosts DBFan-out workerspush post ids to followersFollow graphwho follows whomTimeline cacheone list per userTimeline servicemerges celebrity posts atread timeSearch indexSearch service

Which kind of system is this?

Driver appsends GPS every ~4 sRider appsees the driver approachLocation gatewayWebSocketLocation serviceGeospatial indexin memory, by area cellMatching servicenearest available driverTrip serviceTrips DBPricing servicesurge by supply and demandPayments

Which kind of system is this?

Sender's phoneConnection gatewaypersistent WebSocket perphoneChat serviceroutes by recipient; sentand delivered receiptsUndelivered messageskept until deliveredRecipient's phonePresence serviceonline, last seenPush notificationswakes offline phonesKey directorypublic keys for end-to-endencryptionMedia storageencrypted; recipientdownloads by linkConnection gatewayrecipient's WebSocket

Which kind of system is this?

Done

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