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Designing an API for Mobile - SocialRadar

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Designing an API for mobile - Lessons we've learned at SocialRadar. Given at API Craft DMV meetup in April 2014.

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Designing an API for Mobile - SocialRadar

  1. 1. Victor Quinn @victorquinn Lead Node.js Engineer Designing an API for Mobile API Craft DMV Meetup, April 28 2014
  2. 2. Download Gives you real-time information on the people around you ! It’s free!! ! This will be pretty fast-paced More About SocialRadar
  3. 3. Special considerations for a Mobile API • Speed really matters • Battery usage - minimize • Maximizing network utilization • Response size matters • Minimize number of requests • Stateless
  4. 4. Speed: Problems • Only one thing on screen at a time, perception change • On desktop other things can distract • Best Case: ~400ms latency for round trip on cell network • We tested at SocialRadar using a basic ping no-op endpoint • Verizon LTE, iPhone 5S • Device doesn’t maintain active connection • Average case much worse, ~1000ms round trip
  5. 5. Ideal round trip iPhone 5S on Verizon LTE User's Phone API 200ms 200ms 200ms Total round trip time 800ms 200ms bit of hand waving, I’m not a network expert
  6. 6. Likely round trip iPhone 4S on Verizon 3G User's Phone API 500ms 500ms 200ms Total round trip time 1600ms 400ms
  7. 7. Speed: Solutions • Cache anything humanly possible • Respond as quickly as possible, deferring anything that doesn’t need to be done immediately • Queue most things • Make sure your API can handle high concurrency (we settled on Node.js to accomplish this, WhatsApp uses Erlang)
  8. 8. Minimize battery usage ! • Brief note about cell battery and network usage (more) • Response size matters • Minimize number of requests Maximize network utilization
  9. 9. Response Size: Problems • At SocialRadar, we tested responses of different sizes • Optimal was largest response that would fit into a single TCP packet on the cell network. • Around 128KB. Differs based on client device and network • Any longer would jump response time significantly
  10. 10. Response Size: Solutions • Paging sizes — largest that fit within TCP packet window • Contrast with Desktop, paging more dependent on server response time and UI
  11. 11. User's Phone API 200ms 200ms 200ms Total round trip time 800ms 200ms Page size of 20 users To retrieve 100 users, ~4s Paging Size: 20 (Ideal)
  12. 12. Paging Size: 50 (Ideal) User's Phone API 200ms 200ms 500ms Total round trip time 1100ms 200ms Page size of 50 users To retrieve 100 users, ~2.2s
  13. 13. Paging Size: 20 (Likely) User's Phone API 500ms 500ms 200ms Total round trip time 1600ms 400ms To retrieve 100 users, ~8s
  14. 14. Paging Size: 50 (Likely) User's Phone API 500ms 500ms 500ms Total round trip time 1900ms 400ms To retrieve 100 users, ~3.8s
  15. 15. Number of Requests: Problems • Traditionally parallelized, not (well) on mobile • Battery life is of great concern and every network request eats into that • Spinning up the cell modem, making request, waiting for it drains the battery • So if you make 5 requests instead of 1, draining battery, leaving user waiting
  16. 16. Number of Requests: Solutions • Paging size as mentioned above, try to maximize response that will fit in a packet to minimize the number of requests • So one request with 20KB much better than 5 with 4KB each • Batch multiple requests into a single one
  17. 17. Batch Request Library • Finding no great existing batch request library for Node.js, we rolled our own open source library • http://batch-request.socialradar.com • Allows you to send a single request that represents multiple • No need to compromise on RESTful principles and move to a SOA • Handles complex dependencies
  18. 18. Batch Request Library (2) 1. npm install batch-request 2. Add one line of code to your API:
 app.post('/batch', batch.validate, batch);! 3. Send batch request as single POST:
 {
 "myRequest1": {
 "method": "GET",
 "uri": "http://api.mysite.com/users/1/first_name"
 },
 "myRequest2": {
 "method": "GET",
 "uri": "http://api.mysite.com/users/1/email"
 }
 }
  19. 19. Batch Request Library (3) 4. Receive single response:
 {
 "myRequest1": {
 “statusCode": 200,
 “body": “Victor”,
 “headers”: {…}
 },
 "myRequest2": {
 “statusCode": 200,
 “body": “victor@socialradar.com”,
 “headers”: {…}
 }
 }
  20. 20. When you pull to refresh, Batch Request to: • Update user location with latest GPS reading • Retrieve current City/State • Retrieve most recent stat numbers • Get some user lists to cache them
  21. 21. Stateless • Cell networks are spotty • For performance, want load balance among multiple servers • Solution: Assign access token to device rather than relying on sessions for user access • We have an access token which is an encrypted string containing user_id and some other stuff
  22. 22. Victor Quinn @victorquinn Lead Node.js Engineer ! Download our App Questions?

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