Next.jsでproductionビルド後に`Couldn't find a `pages` directory. というエラーが出る

現象

next.js/examples/custom-server-typescript at canary · zeit/next.js

上記のcustom-server-typescriptに近い環境。

Docker内で.nextや.distをコピーして元のpagesやsrcはない状態。

起動すると以下のようなエラーが発生する。

frontend_1  | /node_modules/next/dist/lib/find-pages-dir.js:3
frontend_1  | if(existsSync(_path.default.join(dir,'..','pages'))){throw new Error('> No `pages` directory found. Did you mean to run `next` in the parent (`../`) directory?');}throw new Error("> Couldn't find a `pages` directory. Please create one under the project root");}
frontend_1  |                                                                                                                                                                    ^
frontend_1  | 
frontend_1  | Error: > Couldn't find a `pages` directory. Please create one under the project root
frontend_1  |     at findPagesDir (/node_modules/next/dist/lib/find-pages-dir.js:3:170)
frontend_1  |     at new DevServer (/node_modules/next/dist/server/next-dev-server.js:1:3830)
frontend_1  |     at Object.createServer [as default] (/node_modules/next/dist/server/next.js:2:105)
frontend_1  |     at Object.<anonymous> (/dist/server/server.js:11:27)
frontend_1  |     at Module._compile (internal/modules/cjs/loader.js:1158:30)
frontend_1  |     at Object.Module._extensions..js (internal/modules/cjs/loader.js:1178:10)
frontend_1  |     at Module.load (internal/modules/cjs/loader.js:1002:32)
frontend_1  |     at Function.Module._load (internal/modules/cjs/loader.js:901:14)
frontend_1  |     at Function.executeUserEntryPoint [as runMain] (internal/modules/run_main.js:74:12)
frontend_1  |     at internal/main/run_main_module.js:18:47

解決

NODE_ENV=production が必要。指定すると解決。