mirror of https://github.com/frappe/gunicorn.git synced 2026-07-01 18:21:30 +08:00

Benoit Chesneau 66d0880c74 Address PR #3468 review feedback

- Guard early_hints callback against calls after response started
- Fix :authority precedence over Host header per RFC 9113 section 8.3.1
- Add nginx early_hints documentation link
- Use standard port 443 in curl examples

2026-01-27 09:59:35 +01:00

8.0 KiB

Raw Blame History

HTTP/2 Support

!!! warning "Beta Feature" HTTP/2 support is a beta feature introduced in Gunicorn 25.0.0. While it has been tested, the API and behavior may change in future releases. Please report any issues on GitHub.

Gunicorn supports HTTP/2 (RFC 7540) for improved performance with modern clients. HTTP/2 provides multiplexed streams, header compression, and other optimizations over HTTP/1.1.

Quick Start

# Install gunicorn with HTTP/2 support
pip install gunicorn[http2]

# Run with HTTP/2 enabled (requires SSL)
gunicorn myapp:app \
    --worker-class gthread \
    --threads 4 \
    --certfile server.crt \
    --keyfile server.key \
    --http-protocols h2,h1

Requirements

HTTP/2 support requires:

SSL/TLS: HTTP/2 uses ALPN (Application-Layer Protocol Negotiation) which requires an encrypted connection
h2 library: Install with pip install gunicorn[http2] or pip install h2
Compatible worker: gthread, gevent, eventlet, or ASGI workers

Configuration

Enable HTTP/2

Enable HTTP/2 by setting the --http-protocols option:

gunicorn myapp:app --http-protocols h2,h1

Or in a configuration file:

# gunicorn.conf.py
http_protocols = ["h2", "h1"]

The order matters for ALPN negotiation - protocols are tried in order of preference.

Protocol	Description
`h2`	HTTP/2 over TLS
`h1`	HTTP/1.1 (fallback)

!!! note Always include h1 as a fallback for clients that don't support HTTP/2.

SSL/TLS Configuration

HTTP/2 requires SSL/TLS. Configure certificates:

gunicorn myapp:app \
    --certfile /path/to/server.crt \
    --keyfile /path/to/server.key \
    --http-protocols h2,h1

Or in a configuration file:

# gunicorn.conf.py
certfile = "/path/to/server.crt"
keyfile = "/path/to/server.key"
http_protocols = ["h2", "h1"]

HTTP/2 Settings

Fine-tune HTTP/2 behavior with these settings:

Setting	Default	Description
`http2_max_concurrent_streams`	100	Maximum concurrent streams per connection
`http2_initial_window_size`	65535	Initial flow control window size (bytes)
`http2_max_frame_size`	16384	Maximum frame size (bytes)
`http2_max_header_list_size`	65536	Maximum header list size (bytes)

Example configuration:

# gunicorn.conf.py
http_protocols = ["h2", "h1"]
http2_max_concurrent_streams = 200
http2_initial_window_size = 1048576  # 1MB

Worker Compatibility

Not all workers support HTTP/2:

Worker	HTTP/2 Support	Notes
`sync`	No	Single-threaded, cannot multiplex streams
`gthread`	Yes	Recommended for HTTP/2
`gevent`	Yes	Requires gevent
`eventlet`	Yes	Requires eventlet
`asgi`	Yes	For async frameworks
`tornado`	No	Tornado handles its own protocol

If you use the sync or tornado worker with HTTP/2 enabled, Gunicorn will log a warning and fall back to HTTP/1.1.

Recommended: gthread Worker

For HTTP/2, the gthread worker is recommended:

gunicorn myapp:app \
    --worker-class gthread \
    --threads 4 \
    --workers 2 \
    --http-protocols h2,h1 \
    --certfile server.crt \
    --keyfile server.key

HTTP 103 Early Hints

Gunicorn supports HTTP 103 Early Hints (RFC 8297), allowing servers to send resource hints before the final response. This enables browsers to preload CSS, JavaScript, and other assets in parallel.

WSGI Applications

Use the wsgi.early_hints callback in your WSGI application:

def app(environ, start_response):
    # Send early hints if available
    if 'wsgi.early_hints' in environ:
        environ['wsgi.early_hints']([
            ('Link', '</style.css>; rel=preload; as=style'),
            ('Link', '</app.js>; rel=preload; as=script'),
        ])

    # Continue with the actual response
    start_response('200 OK', [('Content-Type', 'text/html')])
    return [b'<html>...</html>']

ASGI Applications

Use the http.response.informational message type:

async def app(scope, receive, send):
    # Send early hints
    await send({
        "type": "http.response.informational",
        "status": 103,
        "headers": [
            (b"link", b"</style.css>; rel=preload; as=style"),
            (b"link", b"</app.js>; rel=preload; as=script"),
        ],
    })

    # Send the actual response
    await send({
        "type": "http.response.start",
        "status": 200,
        "headers": [(b"content-type", b"text/html")],
    })
    await send({
        "type": "http.response.body",
        "body": b"<html>...</html>",
    })

!!! note Early hints are only sent to HTTP/1.1+ clients. HTTP/1.0 clients silently ignore the callback since they don't support 1xx responses.

Production Deployment

With Nginx

Configure nginx to proxy HTTP/2 connections to Gunicorn:

upstream gunicorn {
    server 127.0.0.1:8443;
    keepalive 32;
}

server {
    listen 443 ssl;
    http2 on;
    server_name example.com;

    ssl_certificate /path/to/server.crt;
    ssl_certificate_key /path/to/server.key;
    ssl_protocols TLSv1.2 TLSv1.3;

    # Forward 103 Early Hints (requires nginx 1.29+)
    location / {
        proxy_pass https://gunicorn;
        proxy_http_version 1.1;
        proxy_ssl_verify off;

        early_hints $http2;

        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto $scheme;
    }
}

!!! note For nginx to forward 103 Early Hints from upstream, you need nginx 1.29+ and the early_hints directive.

Direct TLS Termination

For simpler deployments, Gunicorn can terminate TLS directly:

# gunicorn.conf.py
bind = "0.0.0.0:443"
worker_class = "gthread"
threads = 4
workers = 4

# SSL
certfile = "/etc/letsencrypt/live/example.com/fullchain.pem"
keyfile = "/etc/letsencrypt/live/example.com/privkey.pem"

# HTTP/2
http_protocols = ["h2", "h1"]
http2_max_concurrent_streams = 100

Recommended Settings

For production HTTP/2 deployments:

# gunicorn.conf.py
worker_class = "gthread"
workers = 4
threads = 4
keepalive = 120  # HTTP/2 connections are long-lived

# SSL/TLS
certfile = "/path/to/server.crt"
keyfile = "/path/to/server.key"
ssl_version = "TLSv1_2"  # Minimum TLS 1.2 for HTTP/2

# HTTP/2
http_protocols = ["h2", "h1"]
http2_max_concurrent_streams = 100
http2_initial_window_size = 65535

Troubleshooting

HTTP/2 not negotiated

If clients fall back to HTTP/1.1:

Verify SSL is configured correctly
Check that h2 is in --http-protocols
Ensure the h2 library is installed: pip install h2
Verify ALPN support: openssl s_client -alpn h2 -connect host:port

Worker doesn't support HTTP/2

If you see "HTTP/2 is not supported by the sync worker":

# Switch to gthread worker
gunicorn myapp:app --worker-class gthread --threads 4

Connection errors with large requests

Increase flow control window sizes:

http2_initial_window_size = 1048576  # 1MB
http2_max_frame_size = 32768  # 32KB

Too many concurrent streams

If clients report stream limit errors:

http2_max_concurrent_streams = 200  # Increase from default 100

Testing HTTP/2

Using curl

# Check HTTP/2 support
curl -v --http2 https://localhost:443/

# Force HTTP/2
curl --http2-prior-knowledge https://localhost:443/

Using Python

import httpx

with httpx.Client(http2=True, verify=False) as client:
    response = client.get("https://localhost:8443/")
    print(f"HTTP Version: {response.http_version}")

8.0 KiB Raw Blame History