Postmortem: outage after upgrading to Next.js 5

[mrtnzlml]

Deploy failed, the website returns Internal Server Error, monitoring reports:

Unable to Connect at 2/5/2018 3:14:21 PM (UTC-06:00) Central Time (US & Canada)

CloudWatch log:

2018-02-05T21:10:19.952Z	f80e5830-0ab8-11e8-bdeb-a910c6df6046	{ Error: Cannot find module '/home/travis/build/mrtnzlml/zlml.cz/node_modules/next/dist/pages/_error.js'
at Function.Module._resolveFilename (module.js:469:15)
at Function.Module._load (module.js:417:25)
at Module.require (module.js:497:17)
at require (internal/module.js:20:19)
at Object.398 (/var/task/.next/dist/bundles/pages/_error.js:86:18)
at __webpack_require__ (/var/task/.next/dist/bundles/pages/_error.js:23:31)
at Object.397 (/var/task/.next/dist/bundles/pages/_error.js:78:18)
at __webpack_require__ (/var/task/.next/dist/bundles/pages/_error.js:23:31)
at /var/task/.next/dist/bundles/pages/_error.js:70:18
at Object.<anonymous> (/var/task/.next/dist/bundles/pages/_error.js:73:10) code: 'MODULE_NOT_FOUND' }

Deleted CI cache, restarted last CI job, same error. Works on a local machine.

Reverting last changes (back to version ^4). Problem fixed:

Connection Successful at 2/5/2018 3:32:11 PM (UTC-06:00) Central Time (US & Canada) after being down for 17 minutes, 50 seconds

Further investigation needed - see testing https://adeira.cz/ (same problem). Possibly related issue: vercel/next.js#3533