Add redirector worker

[alexgibson]

• Add redirector worker for Direct traffic at CRO sandbox versions of pages mozilla/bedrock#7652.
• Add unit tests.
• Update readme.

[alexgibson]

@jgmize r?

[pmac]

It seems possible to return the bedrock response directly instead of redirecting. Would that be desirable, or do we for analytics and/or SEO reasons not want to do that?

[alexgibson]

It seems possible to return the bedrock response directly instead of redirecting. Would that be desirable, or do we for analytics and/or SEO reasons not want to do that?

I think the answer here is that shadowing could confuse Google since the content would keep changing, but let me double check with Raphael.

[alexgibson]

Ok, I double checked with Raphael and he says as long as our experimental pages have a canonical that points to the original URLs (which they do), then a 302 is fine. Shadowing is also ok, but only as long as experiments aren't drastically changing the page. Shadowing is a little more risky, since copy changes could essentially get indexed.

[bookshelfdave]

wow, never thought I'd see dollarshaveclub in a PR :-)

[alexgibson]

@jgmize I pushed a commit with some review fixes, plus a couple of other small details. Here's a summary:

• Removed origin as a variable (switching to relative paths in the config).
• Set sample rate for /en-US/firefox/new/ to 6%.
• Added an additional unit test that checks query params are being preserved on redirect URLs.
• Unit tests now use https://bedrock-stage.gcp.moz.works/ for an origin, so they won't conflict with a real worker running on www-dev etc.
• Added ESLint config check to CI.
• Added .editorconfig file.

I've set the updated worker script running on https://www.allizom.org/en-US/firefox/new/ and done some manual testing. It still seems to be working as expecte 👍

[jgmize]

Nice work @alexgibson!