树莓派3部署Flask-SSE示例无法连接事件流但Redis有活动

在树莓派3上运行Flask-SSE官方示例代码，网站可正常加载，但页面会弹出提示：Failed to connect to event stream. Is Redis running?。Redis已处于运行状态，通过redis-cli monitor查看有如下活动记录（多次刷新页面产生，始终未收到消息）：

1676659598.612265 [0 [::1]:58788] "SUBSCRIBE" "sse"
1676659616.141010 [0 [::1]:39662] "SUBSCRIBE" "sse"
1676659624.109693 [0 [::1]:54564] "SUBSCRIBE" "sse"
1676659627.603954 [0 [::1]:54578] "PUBLISH" "sse" "{\"data\": {\"message\": \"Hello!\"}, \"type\": \"greeting\"}"
1676659627.614501 [0 [::1]:58788] "UNSUBSCRIBE" "sse"
1676659627.621229 [0 [::1]:39662] "UNSUBSCRIBE" "sse"
1676659651.509510 [0 [::1]:53316] "SUBSCRIBE" "sse"

启动服务的命令：

$ sudo systemctl start nginx
$ redis-server --daemonize yes
$ gunicorn sse:app --worker-class gevent --workers=3 --bind 127.0.0.1:8000 --daemon

Python代码：

from flask import Flask, render_template
from flask_sse import sse

app = Flask(__name__)
app.config["REDIS_URL"] = "redis://localhost"
app.register_blueprint(sse, url_prefix='/stream')

@app.route('/')
def index():
    return render_template("index.html")

@app.route('/hello')
def publish_hello():
    sse.publish({"message": "Hello!"}, type='greeting')
    return "Message sent!"

index.html代码：

<!DOCTYPE html>
<html>
<head>
  <title>Flask-SSE Quickstart</title>
</head>
<body>
  <h1>Flask-SSE Quickstart</h1>
  <script>
    var source = new EventSource("{{ url_for('sse.stream') }}");
    source.addEventListener('greeting', function(event) {
        var data = JSON.parse(event.data);
        alert("The server says " + data.message);
    }, false);
    source.addEventListener('error', function(event) {
        alert("Failed to connect to event stream. Is Redis running?");
    }, false);
  </script>
</body>
</html>

1. 修复Nginx反向代理配置 #

Nginx默认的缓冲配置会中断SSE长连接，需在对应location块中添加SSE支持配置：

location / {
    proxy_pass http://127.0.0.1:8000;
    proxy_set_header Host $host;
    proxy_set_header X-Real-IP $remote_addr;
    # 关键：禁用缓冲，保持长连接
    proxy_buffering off;
    proxy_cache off;
    proxy_set_header Connection '';
    proxy_http_version 1.1;
    chunked_transfer_encoding off;
}

location /stream {
    proxy_pass http://127.0.0.1:8000/stream;
    proxy_set_header Host $host;
    proxy_set_header X-Real-IP $remote_addr;
    proxy_buffering off;
    proxy_cache off;
    proxy_set_header Connection '';
    proxy_http_version 1.1;
    chunked_transfer_encoding off;
}

修改完成后重启Nginx：sudo systemctl restart nginx

2. 调整Gunicorn Worker数量 #

使用gevent多worker时，每个worker会独立订阅Redis，发布的消息只会被其中一个worker接收，其他worker的订阅会因超时而断开。测试阶段建议将worker数改为1：

gunicorn sse:app --worker-class gevent --workers=1 --bind 127.0.0.1:8000 --daemon

若需多worker支持，需使用Redis pub/sub的共享连接机制，或采用集群模式部署。

3. 验证EventSource请求状态 #

打开浏览器开发者工具（F12），切换到Network标签，查看EventSource对应的请求：

• 确认请求URL是否正确匹配/stream路径
• 检查响应状态码是否为200
• 确认响应头包含Content-Type: text/event-stream

4. 确认Redis连接有效性 #

通过redis-cli ping测试本地Redis连接，若返回PONG则连接正常。若Redis设置了密码，需修改Flask配置中的Redis URL：app.config["REDIS_URL"] = "redis://:your_password@localhost"

内容的提问来源于stack exchange，提问作者Adam