V2: Server Sent Events from Flask to Caddy via Gunicorn

[kittymagician]

1. My Caddy version (caddy version):

v2.0.0-rc.3

2. How I run Caddy:

caddy start

a. System environment:

Ubuntu 18.04LTS

b. Command:

gunicorn --bind 0.0.0.0:5000 wsgi:app --daemon

d. My complete Caddyfile or JSON config:

demo.domain.com {
    root * /var/www/Project
    tls email@domain.com
    reverse_proxy localhost:5000 {
        header_up Host {http.request.host}
        header_up X-Real-IP {http.request.remote.host}
        header_up X-Forwarded-For {http.request.remote.host}
        header_up X-Forwarded-Port {http.request.port}
        header_up X-Forwarded-Proto {http.request.scheme}
    }
    header {
        X-Content-Type-Options nosnif
        X-Frame-Options DENY
        Referrer-Policy no-referrer-when-downgrade
   }
}

3. The problem I’m having:

I have developed a flask application that relies on Server Sent Events. The application works fine with gunicorn if I connect to the application directly and via flask as well but connecting via Caddy results in no SSE events being sent and no communication made to the /stream endpoint. I’ve seen in v1 of Caddy there was a suggestion to disable gzip. Not sure if I’m doing anything wrong with my configuration file.

4. Error messages and/or full log output:

127.0.0.1 - - [03/May/2020 00:59:30] “GET /stream/1 HTTP/1.1” 200 -

root@VirtQueue:/var/www/VirtQueue# caddy run
2020/05/03 01:25:18.099 INFO using adjacent Caddyfile
2020/05/03 01:25:18.101 INFO admin admin endpoint started {“address”: “tcp/localhost:2019”, “enforce_origin”: false, “origins”: [“localhost:2019”, “[::1]:2019”, “127.0.0.1:2019”]}
2020/05/03 01:25:18.101 INFO http enabling automatic HTTP->HTTPS redirects {“server_name”: “srv0”}
2020/05/03 01:25:18.102 INFO tls cleaned up storage units
2020/05/03 01:25:18.102 INFO http enabling automatic TLS certificate management {“domains”: [“domain.com”]}
2020/05/03 01:25:18.114 INFO autosaved config {“file”: “/root/.config/caddy/autosave.json”}
2020/05/03 01:25:18.114 INFO serving initial configuration
2020/05/03 01:25:18 [INFO][cache:0xc00059f130] Started certificate maintenance routine

5. What I already tried:

Consulted documentation. Looked on GitHub. Chatted to some people in the Discord Server. Still unable to get Caddy to comply.

6. Links to relevant resources:

How to proxy Server Sent Events? · Issue #677 · caddyserver/caddy · GitHub - I can’t see the config example provided as it’s been removed

[matt (Matt Holt)]

Welcome @kittymagician -

As per the docs, try setting flush_interval -1 and see what happens.

I think you can also get rid of:

        header_up Host {http.request.host}
        header_up X-Forwarded-For {http.request.remote.host}
        header_up X-Forwarded-Proto {http.request.scheme}

You can get rid of the others too unless gunicorn actually needs them.

[kittymagician]

Posting up my config in case others get stuck.

Thank you so much for your help and speed @matt That kept me up until the early hours of the morning disabling buffering worked a charm.

demo.domain.com {
    root * /var/www/Project
    tls email@domain.com
    reverse_proxy localhost:5000 {
        flush_interval -1
    }
    header {
        X-Content-Type-Options nosnif
        X-Frame-Options DENY
        Referrer-Policy no-referrer-when-downgrade
   }
}

Thanks again!

[matt (Matt Holt)]

Great!

FYI your nosniff is missing an f.