108: Peeling the Onion on Networking

iOhYes

Discussion

Testing normal networks (aka, not the US)

• 62.5% of the world’s 3.2 Billion internet users have 2G connections (or worse). That number is growing. LTE speeds aren’t going to catch up for at least a decade if not much longer.
• When building robust networking between your client apps and your services, the common case should be the default case. AKA: not WiFi and not LTE.
• Things that help a great deal:
  • Test on 2G and flaky networks
    • Helps to do real world testing in parking garages, elevators and in transit.
    • Simulation will be the highest reproducible ROI way to test
  • Fail fast and accurately. Timeouts play a part in this.
  • Be dynamic with how you handle the network.
    • Slower speeds should have less networking
  • Use modern tech, like HTTP/2
  • Defer, defer, defer (and prioritize)
  • Robustly handle errors
    • If at first you don’t succeed, try again! And again and again. Retry policies can get you from one-9 of success to three-9s very simply.
  • Design your network API in a robust manner!
• Simulating bad connections:
  • Using Network Link Conditioner - iOS and Mac
  • Simulation over WiFi with router firmware
  • Simulation by throttling via your network services with custom headers
  • Simulation in your app by controlling the flow of data being received
    • Expert mode: drop down to the TCP level!

• Timeouts

  • List of timeouts:
    • TCP: connection timeout (TLS connection timeout too), SYN timeout, keepalive/idle timeout, retransmission timeout
    • NSURL: request timeout (max time between data being received in response - default is 60 seconds), resource timeout (time for entire transfer to complete - default is 7 days)
    • Custom timeouts: transaction timeouts (time from initiation to completion including redirects and retries), queue timeout (how long can the request be queued without starting before it times), idle timeout (how long can a request do nothing regarding upload or download before timeout)
  • NSURLSession has a problem with scale. Every different configuration setting requires another NSURLSession to be maintained and managed. Timeouts, different default headers, different TLS settings, different cookie settings, different NSURLCache, cellular vs non-cellular

• Robust API design

  • Transactional APIs
  • Robust error codes (not just HTTP status codes!)
• Retry policies to the rescue

Picks

Darryl

• Pain Free Constraints with Layout Anchors - A bit of follow-up from last week’s episode. I felt like John and I were having trouble explaining anchors, and I remembered this article from a few weeks back.

Nolan

• Performance Culture

Alternative show title suggestions

• Just remember: You’re wrong
• Not all requests are made equal
• Item potency