chain proxy in case of error

[temsa]

Something I try to do with node-http-proxy for some days now, is chaining proxies in case of error : I have multiple middle server. During a delivery, at least one server will be down for a while, so I'd like, if I get an ECONNREFUSED (or a hangup, but it happens for now in about 240s, I guess 2x 120s timeout, and I didn't get how to change this), I'd like my proxy to try another host instead of returning an error I could avoid<

I've created a first proxy, I listen to the "proxyError" event, which is fired, then I ask a second proxy to handle that request and try another equivalent host), it tries to handle the request then I have a "start" event as well for it, but it never writes to my response. My response is writable because I can write to it then call res.end().

I didn't get why for now. Is it possible to do?

[indexzero]

Are you buffering the request? You need to be doing buffering because you will need to re-emit the data and end events so that it gets written to the second response.

Can you provide a code sample? I can probably help you quickly; if you're not familiar with event buffering it can be tricky to get right.

[temsa]

I haven't the code with me and my implementation is pretty naive with no buffering, just chaining 2 RoutingProxy (tried also with RoutingProxy + create a HttpProxy in case of error).

I'm not familiar with event buffering yet (or maybe; but I didn't know it is called like this), so I'll just post here an example tomorrow (it's >2:00am here) and hope for help ;)

[bearnard]

I'm also looking into getting this working, would buffering the request cause significant performance issues?

Charlie, If you have some pointers on where to start re the event buffering that would be great.

[bearnard]

Hi, I'm trying to do something like this:

var buffer = httpProxy.buffer(req);
var buffer2 = httpProxy.buffer(req);

var primary_backend = "10.0.0.1";
var failover_backend = "10.0.0.2";

    proxy.on('proxyError', function(err, req, res){
        proxy.proxyRequest(req, res, {
            host: failover_backend,
            port: 80,
            buffer: buffer2
        });
    });

    proxy.proxyRequest(req, res, {
        host: primary_backend,
        port: 80,  
        buffer: buffer
    }); 

});

while this works for the 1st fe hundred requests, after about 300 or so I see a whole bunch of these errors:

response.resume error: Cannot resume() closed Socket.

Clearly I'm doing something wrong.

I wonder if it would be a nice feature to have proxyRequest accept multiple backends to try.

var primary_backend = ["10.0.0.1","80]
var failover_backend = ["10.0.0.2","80]
proxy.proxyRequest(req, res, {
        backends: [primary_backend, failover_backend] 
        buffer: buffer
    }); 

or something along those lines?

So to get back to my problem, what is the correct way to go about achieving this desired "failover"?.

Bearn.

[bearnard]

any suggestions on this?

[indexzero]

@bearnard I'm not sure there is a workable solution here. The proxyError event may be raised after the response has been partially written to or closed.

Consider the scenario when the first backend fails midway through the response. It is impossible for the proxy to know at what point of the response the reverse proxy request errored.

My suggestion would be to pass a mock response object to proxy.proxyRequest which buffers the response into memory and when it ends then writes it back to the actualy res. This way you can discard the entirety of the data returned from the backend that failed and try all over again.

[indexzero]

This should be fixed by #374 since the proxyError event is only raised once now.

[ntdunglc]

Is there any workaround for this problem after 2 years?