Deploying a high traffic web app without downtime - getting 404 for files from the previous version

Support
,
#1

Scripts in my app are in chunks, some are being loaded immediately, some shortly after everything else was loaded and the others based on user actions. I have a problem where users are requesting files that no longer exists because they loaded an app with version X and then there was a deployment of the new one.

I use a build script that auto-generates file name so it looks like this: 3.eebedef8.chunk.js
In theory, I could make them look always the same but then I risk that a user would run code from two versions at the same time.

An article that nicely explains the problem:
https://www.rea-group.com/blog/static-assets-in-an-eventually-consistent-webapp-deployment/

#2

Hi @Pentiado, looks like you are changing your filename on each deploy. Have you checked out the following post about that? [Common Issue] Making the most of Netlify's CDN cache

#3

Hey @Dennis!

What you’re suggesting I don’t think is a direct solution to the problem I’m facing but it could change it.
If I keep the filenames on each deploy then people using my app will end up having scripts from two different versions running at the same time.

An example:
When user opens root page it pulls index.js and vendor.js (with all packages). Then once the user goes to /video page it dynamically requests video.js. If I deployed changes when a user was on root page that involved extra library then going to /video is going to crash because that library was never loaded.
So the strategy you’re suggesting makes sense only if every js chunk is fully independent.

#4

What Dennis was attempting to suggest was that you will likely need to change your app architecture since indeed, we don’t keep a copy of the old stuff around - only what you have just built is pushed live. This is probably a more straightforward description of the problem and possible changes:

You could of course push the “old” files to cache at the end of the old build, and restore them during new build using something like https://www.npmjs.com/package/cache-me-outside - but then, how will you ever get your visitors updated to the new code if you allow them to use the old? Tis a problem you’ll have to solve somehow :slight_smile: