Turn export service into a Vercel serverless function #3095

taneliang · 2020-12-29T11:12:12Z

Context

Stacked on #3092. Part of #3098, work to dedockerize NUSMods to streamline our deployment processes.

Observations

Cold startup time can take a while (~6s?), but I think it's well worth it.
No docs, but I think we should just update all the docs at once go once we've removed Docker.
Not sure if local dev environment is working. I couldn't get vercel dev to work locally, but I think that may just be because I'm using WSL. We could just fix this in a future PR.
The /export project has quite a bit of code that's not used, specifically the PM2 deployment and ability to load timetable data from the filesystem. With the move to serverless, all the router stuff will also not be needed anymore. I've left all the old code untouched in case this serverless stuff doesn't work out.
If we do decide to keep this serverless setup for good, we'll want to consider inlining the /export project into /website. This will allow us to have a working export button in every deploy 😍

Biggest risks

Not sure if we'll hit any pricing limits, but I guess we'll find out once real traffic comes in with the semester starting.

Test URLs

Image export
PDF export
422 page: https://nusmods-export-git-eliang-vercel-export.nusmodifications.vercel.app/api/export/pdf
404 page: just visit any random path

TODO after this PR

Set up export.nusmods.com DNS records
Update /website to use https://export.nusmods.com/api/export as the export base URL
Point nusmods.com to Vercel 🎉
Docs

vercel · 2020-12-29T11:12:14Z

This pull request is being automatically deployed with Vercel (learn more).
To see the status of your deployments, click below or on the icon next to each commit.

nusmods-website – ./website

🔍 Inspect: https://vercel.com/nusmodifications/nusmods-website/dhkenhm8x
✅ Preview: https://nusmods-website-git-eliang-vercel-export.nusmodifications.vercel.app

nusmods-export – ./export

🔍 Inspect: https://vercel.com/nusmodifications/nusmods-export/r3ub9qji4
✅ Preview: https://nusmods-export-git-eliang-vercel-export.nusmodifications.vercel.app

codecov · 2020-12-29T11:15:18Z

Codecov Report

Merging #3095 (071d895) into master (a76344a) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #3095   +/-   ##
=======================================
  Coverage   55.58%   55.58%           
=======================================
  Files         255      255           
  Lines        5311     5311           
  Branches     1218     1218           
=======================================
  Hits         2952     2952           
  Misses       2359     2359

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nusmods-deploy-bot · 2020-12-29T11:16:19Z

Deployment preview for 071d895b ready at http://5fec891decca618e5b7df837--nusmods-deploy-preview.netlify.app

ZhangYiJiang

Looks good as a direct port, but you might want to restructure the code a bit more since the code looks like it has a lot of copy-pasted chunks from the old Koa middleware code

ZhangYiJiang · 2020-12-29T18:37:00Z

export/api/export/image.ts

+    const dataCandidate = JSON.parse(request.query.data as never);
+    validateExportData(dataCandidate);
+    data = dataCandidate;


What is that as never cast? Isn't this the same as

data = JSON.parse(request.query.data); validateExportData(data);

Nope:

Figured we should cast to never instead of the ideal string type since we aren't actually sure.

ZhangYiJiang · 2020-12-29T18:39:29Z

export/api/export/image.ts

+const handler: NowApiHandler = async (request, response) => {
+  try {
+    await main(request, response);
+  } catch (e) {
+    const eventId = Sentry.captureException(e.original || e);
+
+    console.error(e);
+
+    if (e instanceof HttpError) {
+      if (e.code === 422) {
+        response.status(422).send(render422());
+        return;
+      }
+    }
+    response.status(500).send(render500(eventId));
+  }
+};


This should definitely be lifted to a higher order function, and we can probably deduplicate most of the two main functions - right now they are very similar

Hmm okay.

I originally decided against that because I thought we'll want the handler file itself to perform all the response sending and error throwing, so that it's easier to see what's sent back to the client and also to trace the thrown error and where they're caught. So almost all the duplicated code just throws errors and creates responses.

But I drafted a hof and I think it'll still be easy to trace, so let's do that:

function makeHandler<T>( validateData: (request: NowRequest) => T, performExport: (page: Page, data: T, response: NowResponse) => void, ): NowApiHandler { // ... }

ZhangYiJiang · 2020-12-29T18:45:42Z

export/yarn.lock

@@ -286,6 +291,15 @@
  dependencies:
    "@types/node" "*"

+"@vercel/[email protected]":


Man, vercel node bundling it's own TypeScript is super awkward, especially when it diverge from our own version. It seems they forked ts-node for some reason https://github.com/vercel/vercel/blob/master/packages/now-node/src/typescript.ts

Hmm this could be problematic if they use their version of TS in prod

Okay, thankfully they don't.

From the build log (internal-only):

... 22:02:42.582 Using TypeScript 4.1.2 (local user-provided) ...

ZhangYiJiang · 2020-12-29T18:54:31Z

export/api/export/image.ts

+    if (e.message.includes('ERR_CONNECTION_REFUSED')) {
+      throw new HttpError(
+        500,
+        `Could not open the page located at process.env.PAGE (${url}). Try opening it in your browser?`,
+        e,
+      );
+    }


Is this just for local development? If so a local env check + logger log might be better

Not necessarily, if the function was wrongly configured in prod or if nusmods.com goes down for some reason this will be shown too. But it sounds like we can improve this error message so that it'll make more sense in prod

I'm going to leave this message as is because I expect this to only be encountered if the function isn't set up properly. nusmods.com shouldn't ever have downtime unless Vercel goes down, and if that ever happens the serverless functions will probably be dead too.

taneliang · 2020-12-30T04:05:47Z

@ZhangYiJiang Yeah, there's quite a lot of copy pasted code in this PR 😆

I think apart from the handler code duplication discussed above, the other big copy paste is the render.ts -> render-serverless.ts file. I decided to fork it so that our handlers don't import puppeteer, and also so that it'll be easy to delete if/when we decide to drop the old Koa implementation.

I think part of this quick and dirty approach is also just to deploy it to prod and see how well it functions (pun not intended, but ha), before we really clean it up for real.

ZhangYiJiang

Fair - let's go for the MVP then and see how well this works. We should also think of some way of testing this in prod just to see if anything comes up, maybe route a small amount of traffic to this

taneliang · 2020-12-30T04:52:42Z

I think we don’t need progressive rollout for this one. Since the new Vercel-hosted /website will be deployed by a DNS change, we can just change the DNS record back if export (or website) fails. Should be pretty painless. Also, yolo :D

public/styles.css is necessary for the static 404.html.

taneliang · 2020-12-30T14:25:29Z

Rebased on master and added 071d895 (#3095).

taneliang added the export label Dec 29, 2020

vercel bot deployed to Preview – nusmods-export December 29, 2020 12:47 View deployment

vercel bot deployed to Preview – nusmods-website December 29, 2020 12:47 View deployment

vercel bot deployed to Preview – nusmods-export December 29, 2020 12:50 View deployment

vercel bot deployed to Preview – nusmods-website December 29, 2020 12:50 View deployment

vercel bot deployed to Preview – nusmods-website December 29, 2020 14:00 View deployment

vercel bot deployed to Preview – nusmods-export December 29, 2020 14:00 View deployment

vercel bot deployed to Preview – nusmods-website December 29, 2020 14:08 View deployment

vercel bot deployed to Preview – nusmods-export December 29, 2020 14:09 View deployment

vercel bot deployed to Preview – nusmods-website December 29, 2020 14:29 View deployment

vercel bot deployed to Preview – nusmods-export December 29, 2020 14:29 View deployment

taneliang requested a review from a team December 29, 2020 14:42

taneliang marked this pull request as ready for review December 29, 2020 14:42

taneliang mentioned this pull request Dec 29, 2020

Set up /website Vercel deployment #3092

Merged

6 tasks

ZhangYiJiang reviewed Dec 29, 2020

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ZhangYiJiang approved these changes Dec 30, 2020

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Base automatically changed from eliang/vercel to master December 30, 2020 13:29

taneliang added 8 commits December 30, 2020 21:33

Quick and dirty implementation of Vercel serverless export function

026dfee

Fix a bunch of types, improve code flow

088236a

Try to fix headers

f4e8313

Implement image export and clean up code

ee320a2

Use public/styles.css over views/styles.css

5ad68a8

public/styles.css is necessary for the static 404.html.

Try to use our 404.html to replace directory index and /api 404s

658b6a2

Fix styles.css link URL

7739721

Extract export handler creator hof

071d895

taneliang force-pushed the eliang/vercel-export branch from 3c93b58 to 071d895 Compare December 30, 2020 14:01

vercel bot deployed to Preview – nusmods-website December 30, 2020 14:01 View deployment

vercel bot deployed to Preview – nusmods-export December 30, 2020 14:01 View deployment

taneliang merged commit 43c45cf into master Dec 30, 2020

taneliang deleted the eliang/vercel-export branch December 30, 2020 14:07

taneliang mentioned this pull request Dec 30, 2020

Migrate /website and /export from Docker to Vercel #3098

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Turn export service into a Vercel serverless function #3095

Turn export service into a Vercel serverless function #3095

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Turn export service into a Vercel serverless function #3095

Turn export service into a Vercel serverless function #3095

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taneliang commented Dec 29, 2020 • edited Loading

Context

Observations

Biggest risks

Test URLs

TODO after this PR

vercel bot commented Dec 29, 2020 • edited Loading

nusmods-website – ./website

nusmods-export – ./export

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Codecov Report

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