Varnish Cache v4：不正确的后端健康检查响应

Question

我在我的 CMS 前设置了 Varnish Cache (4) 来帮助缓存请求。如果我的 CMS 出现故障，我想在设定的宽限期内交付缓存的项目。我遵循了许多在线提供的示例，但运行遇到了 Varnish 无法识别我的后端已关闭的问题。当我手动关闭 CMS 时，std.health(req.backend_hint)) 继续 return true 并尝试从后端检索项目，然后 return 返回 503 响应。

问题：我是否错误地假设 std.health(req.backend_hint)) 会识别出我的 CMS 已关闭？

这是我用来测试的 VCL 脚本：

sub vcl_recv {
  # Initial State
  set req.http.grace = "none";
  set req.http.x-host = req.http.host;
  set req.http.x-url = req.url;

  return(hash);
}

sub vcl_backend_response {
    set beresp.ttl = 10s;
    set beresp.grace = 1h;
}

sub vcl_deliver {
    # Copy grace to resp so we can tell from client
    set resp.http.grace = req.http.grace;

    # Add debugging headers to cache requests
    if (obj.hits > 0) {
        set resp.http.X-Cache = "HIT";
    }
    else {
        set resp.http.X-Cache = "MISS";
    }
}

sub vcl_hit {
    if (obj.ttl >= 0s) {
        # normal hit
        return (deliver);
    }
    # We have no fresh content, lets look at the cache
    elsif (std.healthy(req.backend_hint)) {
        # Backend is healthy. Limit age to 10s.
        if (obj.ttl + 10s > 0s) {
            set req.http.grace = "normal(limited)";
            return (deliver);
        } else {
            # No candidate for grace. Fetch a fresh object.
            return(fetch);
        }
    } else {
        # backend is sick - use full grace
        if (obj.ttl + obj.grace > 0s) {
            set req.http.grace = "full";
            return (deliver);
        } else {
            # no graced object.
            return (fetch);
        }
    }
}

同样，当我关闭 CMS 时，std.healthy(req.backend_hint)) 仍然报告后端正常并且从不跳转到最后的 else 语句。

感谢观看。

Answer 1

要正确使用 std.healthy，您当然需要配置后端探测。因此，在 VCL 文件的顶部，您首先要配置一个探测器：

probe site_probe {
    .request =
        "HEAD / HTTP/1.1"
        "Host: example.com"
        "Connection: close";
        .interval  = 5s; # check the health of each backend every 5 seconds
        .timeout   = 3s;  # timing out after 1 second by default.
        .window    = 5;  # If 3 out of the last 5 polls succeeded the backend is considered healthy, otherwise it will be marked as sick
        .threshold = 3;
 }

确保将 example.com 替换为您的主要网站域名。放置（或省略）www. 前缀很重要，这样探测器就不会被重定向并标记为失败。

当然，您的后端定义应该配置为使用定义的探测器：

backend default {
    .host = "127.0.0.1";
    .port = "8080";
    .probe = site_probe;
}

Varnish Cache v4：不正确的后端健康检查响应

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