如果 POST 数据很大，GCP HTTP 负载均衡器会返回 502 错误

Question

我们有一个 API 服务器并且正在使用 HTTP 负载均衡器。我们发现如果 HTTP 请求的数据很大，L7 负载均衡器会返回 502 错误。

我们已经确认它在没有负载均衡器的情况下访问 API 时有效（直接访问 API 服务器。）

这个问题可能是一个类似的问题。 HTTP Load Balancer cuts out part of a large request body

有人说使用 L4 网络负载均衡器是一种可能的解决方案，但由于某些原因我们不想使用它，例如基于 URL 的负载均衡和跨区域的负载均衡。

// Response OK (data size is 1024)
curl -H "Content-Type: application/json" -X POST -d '{"xx": "000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"}' https://xxxxxxxxxxxxxxx.com/xx/xxxxxxxxxxxx/xxxxxxxxx

// Response NG (data size is 1025)
curl -H "Content-Type: application/json" -X POST -d '{"xx": "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"}' https://xxxxxxxxxxxxxxx.com/xx/xxxxxxxxxxxx/xxxxxxxxx

似乎LB对post数据的大小有一些限制。测试表明限制在 1024 字节左右。

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更新1

@chaintng saved me。链接帖子上有人说如果帖子数据超过 1024 字节，curl 会添加 "Expect: 100-continue Header"。

// Response NG (data size is 1025. without "Expect: ")
curl -H "Content-Type: application/json" -X POST -d '{"xx": "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"}' https://xxxxxxxxxxxxxxx.com/xx/xxxxxxxxxxxx/xxxxxxxxx

// Response OK (data size is 1025. with "Expect: ")
curl -H "Expect: " -H "Content-Type: application/json" -X POST -d '{"xx": "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"}' https://xxxxxxxxxxxxxxx.com/xx/xxxxxxxxxxxx/xxxxxxxxx

Answer 1

来自这个问题Curl to Google Compute load balancer gets error 502的参考

这是因为 CURL 在请求大型 POST 正文定义标头为 Expect: 100-continue 时具有默认值

Google L7 负载平衡不支持哪些功能（在本文档中声明 https://cloud.google.com/compute/docs/load-balancing/http/）

您所要做的就是在执行 curl 之前通过设置标头来忽略此行为。

例如在 PHP 中 curl_setopt($ch, CURLOPT_HTTPHEADER, ['Expect:']);