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Webflow Reverse-Proxy SSL Issue

Hi! We are using Webflow for our marketing site and we have a Nginx reverse-proxy that sits in front of the Webflow site. It’s a setup that is essentially based on this blog post:

This has been working fine but as of this morning, we’ve noticed the reverse proxy can no longer serve the Webflow site.

Upon investigation, these errors in our Nginx proxy seem like they are the culprit:

2021/11/07 04:27:55 [error] 33#33: *249 SSL_do_handshake() failed (SSL: error:14094438:SSL routines:ssl3_read_bytes:tlsv1 alert internal error:SSL alert number 80) while SSL handshaking to upstream, client: 10.104.9.10, server: , request: "GET /robots.txt HTTP/1.1", upstream: "https://34.218.6.194:443/robots.txt", host: "felt.com"

I’ve searched around, this seems like a common issue that’s generally solved by including the following in the Nginx config, but we already do have it:

proxy_ssl_server_name on;

As well as setting the correct host and everything. Again, our setup was working fine up until very recently and we had no changes on our end.

I should note that our reverse-proxy is actually hosted on Render (a Heroku-like PaaS) platform and their services are behind a Cloudflare server. We’ve however checked with Render, and they’ve noticed no issues on their end.

I’m curious if others have seen an issue come up recently. I’m wondering if Webflow changed how it does SSL or some certificate in the chain somewhere expired. Looking forward to hearing potential solutions from the community.