Wrangler: Bug: Downtime on Site update

[ashleymichal]

When we publish a site worker, often the worker and its accompanying asset manifest make it to the edge ahead of the new KV keys, and/or the "old" KV keys are removed before the worker is updated. This causes a window of downtime when a page is updated. We need to somehow delay removing "old" assets from KV until everything is live. There are a few ways to implement this, will update this issue with possible strategies soon.

[ashleymichal]

community report: https://community.cloudflare.com/t/brief-period-of-unavailability-when-publishing-workers-sites/121929

[dmitryyankowski]

Any updates on this? :) @ashleygwilliams @ashleymichal

[ashleymichal]

hey @lolcoolkat I'll likely be investigating this on Friday, and will comment here with my conclusions.

[dmitryyankowski]

Thank you! @ashleymichal

[ashleymichal]

so here's what happens.

Say i have an asset /sweet-blog-post.html. The first time Wrangler uploads it, it hashes the content and inserts it between the file stem and the extension, e.g. /sweet-blog-post.abcdef1234567890.html, and adds the following entry to the asset manifest:

"/sweet-blog-post.html": "/sweet-blog-post.abcdef.html"

If I update my sweet blog post, the next time Wrangler goes to upload, the content hash changes (e.g. /sweet-blog-post.fedcba.html. Wrangler then compares the local content with the remote content, and deletes the old version, updating the asset manifest to reflect the changes.

Unfortunately, the old version is deleted before the new asset manifest is uploaded with the worker, and so there is a window during which the old worker is trying to reference the deleted asset. This is sub-optimal.

We can reduce this window significantly by delaying deletes until after the worker has been published.

[ashleymichal]

i'm going to defer work on this until the work on Multi-Route support has been approved and merged, there's a lot of changes to the publish command there, and there will be here as well.

My proposed solution implementation:

• wee refactor to separate logic for publishing a site vs publishing a vanilla workers project. this just helps with cognitive load.
• rename kv::bucket::sync to kv::bucket::diff, modify to return tuple (exclude_keys, delete_keys), and have function publish_site call upload before worker publish, and delete after.
• (bonus) refactor to keep bucket logic specific to sites; at the moment only sites have buckets, and i'm not sure we plan to change that; at the moment it's sort of confusing that we have a bucket config on site but also on all kv namespaces.

[ashleymichal]

status update: i've got a good amount of work done locally, but the number of in flight PRs, releases, and feature work being done coupled with a CI bug has me a little nervous about going much further with this, given the number of potential merge conflicts. will resume work once 1.7.0 is out.

[AngusMorton]

@ashleymichal are there any updates for this? This issue is a massive blocker for us, so, if the fix is going to take time then maybe we need to get a smaller interim fix in (e.g. an option to never delete resources from the KV store?).

If I can contribute to getting this solved let me know.