Allow multiple hosts to work around firewall blocks

[aldenquimby]

Background

• Most of our customers are government agencies, who tend to have very restrictive firewalls
• For about 5% of our users, api.knock.com gets blocked, so Knock does not work
• We've been fixing this historically by getting customer IT on the phone and having them add Knock to their allowlist
• But this slows down our implementation, and leads to poor initial UX (notifications don't work at first)

Reverse Proxy

• The existing KnockOption.host let's us work around this, which is great
• We've setup mysite.com/tunnel/knock as a reverse proxy to api.knock.com, and now the firewall blocks are gone
• But this adds latency for 100% of our users to fix a problem that only 5% have

Ask

• We'd like a way to say "use my reverse proxy host, but only if the default host is failing"
• Example React API:

  <KnockProvider hosts={['https://api.knock.app', 'https://mysite.com/tunnel/knock']} ...

• This mirrors how Algolia's javascript client works
  • by default they cycle through 5 domains to ensure high availability of search
  • but you can also add your own, which we've leveraged to solve this exact same problem with Algolia in our app
  • their lib has a lot more complexity (read-only vs write-only hosts, caching host status in local storage, etc) than what we'd need here

Implementation Ideas

• it looks like this logic could be entirely contained to ApiClient
• in the catch of makeRequest (so after 3 failures), if there are multiple hosts, we could re-create axiosClient and socket using the next host in the list, and then try again
• I'd be glad to try a PR with this if it sounds ok

[connorlindsey]

Hey @aldenquimby, thanks for the detailed issue! This would definitely be a nice improvement to the api client but not something we can immediately tackle. If you'd be willing to open a PR, that would be amazing! One note is that we'd prefer to update the host param to accept a string or array rather than introduce an additional property.

[aldenquimby]

Thanks @connorlindsey , I'll give it a shot!