It depends on your speed requirements and whether calls are being sent async or not. Also keep in mind that even with internal apis, an api call is usually multiple network boundaries (service1 --> service2 (potential DNS lookup) --> WAF/security proxy --> Firewall --> Load balancer --> SSL handshake --> server/container firewall --> server/container). Then you get into whether the service you're calling calls other apis etc. You can quickly burn 50ms or more with multiple hops. If you're trying to return responses within 200ms you now have very little margin.