slfan1989 commented on code in PR #8697:
URL: https://github.com/apache/hadoop/pull/8697#discussion_r3888831756
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hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-web-proxy/src/main/java/org/apache/hadoop/yarn/server/webproxy/WebAppProxyServlet.java:
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@@ -310,7 +310,10 @@ private void proxyLink(final HttpServletRequest req,
base.setHeader(name, value);
}
}
-
+ // Tell the AM/history server to close the connection after the response
+ // so that the proxied connection is not left in CLOSE_WAIT state on the
+ // proxy side (YARN-11845).
+ base.setHeader("Connection", "close");
Review Comment:
This also changes the client-facing connection behavior.
`proxyLink()` copies every header from the upstream response into `resp`, so
when the AM/history server responds with `Connection: close`, that hop-by-hop
header is forwarded to the browser/API client as well.
I verified this by checking `proxyConn.getHeaderField("Connection")` in the
new test, and the client-facing response contains `close`.
Consequently, every proxied request loses keep-alive between the client and
WebAppProxy, contrary to the PR description that only the internal connection
is affected. RFC 9110 Section 7.6.1 also requires intermediaries to remove
`Connection` and other connection-specific fields before forwarding.
Could we instead close the locally created
`CloseableHttpClient/CloseableHttpResponse` with try-with-resources, which
directly addresses the resource lifecycle? If the request header is retained,
the response path should filter hop-by-hop headers and the test should verify
that the client-facing connection is not forced closed.
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