CODEWITHSUNDEEP
proxyjetty
chuckd
chuckd

Reputation: 158

What's the right way to retry a proxy request that failed

I have a proxy servlet that is implemented using Jetty's AsyncProxyServlet.Transparent (Jetty 9). Proxied requests are occasionally failing with EarlyEOF exceptions because of the way the remote server sometimes closes connections. In these cases, I would like the proxy to retry the request on behalf of the client instead of returning a 502 status response. What is the correct way to do this?

I assume I need to override AbstractProxyServlet's onProxyResponseFailure method and implement my own error handling, but I'm not sure how to create and send a new proxy request and associate it with the original request from the client.

Upvotes: 2

Views: 1996

Answers (1)

Joakim Erdfelt
Joakim Erdfelt

Reputation: 49515

Proxy retry with AsyncProxyServlet isn't feasible.

The Async nature of both the browser HTTP exchange and the proxied HTTP exchange means they are tied at the hip to each other.

If one fails, both fail, automatically. Its very difficult to retry, as the browser HTTP exchange is already committed and partially completed as well.

In essence, the browser HTTP exchange would need to be suspended, and then the proxy HTTP exchange would need to be restarted, from scratch, then you'll need to "catch up" the exchange on the proxy side to the point where you are on the browser side. Once you are caught up, you'll have to adapt the proxy response to match the techniques for the browser response (things like known content-length, gzip state, chunking, etc..)

This is further complicated if the proxy response changes between requests, even in minor ways (response headers, sizes, compression, content, etc..)

The only way you can accomplish retry is to NOT use async, but use full caching of the proxy response BEFORE you send the response to the client (but this is actually more difficult to implement than the Async proxy techniques, as you have to deal with complex memory, http caching, and timeout concerns)

Upvotes: 2

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