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Open WhatsApp →Open Chat (Slack-style) →

WhatsApp vs Chat (Slack-style)

WhatsApp

WhatsApp

Persistent connections, message queues, delivery.

Components (8)

  • Sender
  • WS Gateway
  • Chat Service
  • Presence
  • Cassandra
  • Kafka
  • APNs / FCM
  • Recipient

Headline numbers

  • Messages / sec (avg)~1.2M/sec
  • Cassandra writes / sec~2.4M/sec
  • Storage / day~12 TB
Chat (Slack-style rooms)

Chat (Slack-style rooms)

Room-based pub/sub fanout across gateway instances.

Components (6)

  • Sender
  • Recipient
  • WS Gateway
  • Chat Service
  • Postgres
  • Redis Pub/Sub

Headline numbers

  • WebSocket connections~10M concurrent
  • Messages / sec~3K avg, ~15K peak
  • Fan-out writes / sec~30K

Key differences

Only in WhatsApp
  • Presence
  • APNs / FCM
In both
  • Client
  • Api Gateway
  • Service
  • Database
  • Queue
Only in Chat (Slack-style)
None.

Flow shape

WhatsApp flows
  • Send message (recipient online)6 steps
  • Send message (recipient offline)7 steps
  • ⚠ APNs / FCM is down7 steps
  • ⚠ WS Gateway box dies3 steps
Chat (Slack-style) flows
  • Send to a room6 steps
  • Reconnect and catch up4 steps
  • ⚠ Redis Pub/Sub is down5 steps