Tuesday 19 September 2017

Crash on app launch for users running iOS 11

Medium Engineering
Oct 6, 2017 · 1 min read

On September 19, 2017, version 3.3 of the Medium iOS app was released to the App Store. Apple released the official version of iOS 11 earlier that same day. Through a combination of factors, the app started crashing on launch for users running iOS 11.


Timeline

  • September 19, 3:22pm: Version 3.3 was released to the App Store.
  • 4:16pm: iOS engineers received an alert from Crashlytics about a crash affecting a large percentage of users on iOS 11 only.
  • 6:03pm: A fix for the crash was submitted in version 3.4 of the app with an expedited review request.
  • September 20, 11:00pm: Version 3.4 of the app was approved and released.

Root cause

The crash was caused by a runtime type mismatch between what type an object was declared to be and what type it was at runtime. This type mismatch was introduced a while ago, but didn’t start causing crashes until iOS 11.


The Medium Engineering team have committed to publishing a technical postmortem for serious outages to Medium core services, in order to build trust and hold us accountable to our users. More background on this program.

Postmortems

In pursuit of transparency, we will publish a public postmortem for any serious outage on core Medium services.

Thanks to Xiao Ma

Medium Engineering

Written by

We are the @Medium engineering team

Postmortems

In pursuit of transparency, we will publish a public postmortem for any serious outage on core Medium services.

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