Nginx upstream prematurely closed connection while reading response header from upstream, for large requests

I am using nginx and node server to serve update requests. I get a gateway timeout when I request an update on large data. I saw this error from the nginx error logs :

2016/04/07 00:46:04 [error] 28599#0: *1 upstream prematurely closed connection while reading response header from upstream, client: 10.0.2.77, server: gis.oneconcern.com, request: "GET /update_mbtiles/atlas19891018000415 HTTP/1.1", upstream: "http://127.0.0.1:7777/update_mbtiles/atlas19891018000415", host: "gis.oneconcern.com"

I googled for the error and tried everything I could, but I still get the error.

My nginx conf has these proxy settings:

    ##
    # Proxy settings
    ##

    proxy_connect_timeout 1000;
    proxy_send_timeout 1000;
    proxy_read_timeout 1000;
    send_timeout 1000;

This is how my server is configured

server {
listen 80;

server_name gis.oneconcern.com;
access_log /home/ubuntu/Tilelive-Server/logs/nginx_access.log;
error_log /home/ubuntu/Tilelive-Server/logs/nginx_error.log;

large_client_header_buffers 8 32k;
location / {
    proxy_pass http://127.0.0.1:7777;
    proxy_redirect off;

    proxy_http_version 1.1;
    proxy_set_header Upgrade $http_upgrade;
    proxy_set_header Connection 'upgrade';
    proxy_set_header Host $http_host;
    proxy_cache_bypass $http_upgrade;
}

location /faults {
    proxy_pass http://127.0.0.1:8888;
    proxy_http_version 1.1;
    proxy_buffers 8 64k;
    proxy_buffer_size 128k;
    proxy_set_header Upgrade $http_upgrade;
    proxy_set_header Connection 'upgrade';
    proxy_set_header Host $host;
    proxy_cache_bypass $http_upgrade;
}

}

I am using a nodejs backend to serve the requests on an aws server. The gateway error shows up only when the update takes a long time (about 3-4 minutes). I do not get any error for smaller updates. Any help will be highly appreciated.

Node js code :

app.get("/update_mbtiles/:earthquake", function(req, res){
var earthquake = req.params.earthquake
var command = spawn(__dirname + '/update_mbtiles.sh', [ earthquake, pg_details ]);
//var output  = [];

command.stdout.on('data', function(chunk) {
//    logger.info(chunk.toString());
//     output.push(chunk.toString());
});

command.stderr.on('data', function(chunk) {
  //  logger.error(chunk.toString());
 //   output.push(chunk.toString());
});

command.on('close', function(code) {
    if (code === 0) {
        logger.info("updating mbtiles successful for " + earthquake);
        tilelive_reload_and_switch_source(earthquake);
        res.send("Completed updating!");
    }
    else {
        logger.error("Error occured while updating " + earthquake);
        res.status(500);
        res.send("Error occured while updating " + earthquake);
    }
});
});

function tilelive_reload_and_switch_source(earthquake_unique_id) {
tilelive.load('mbtiles:///'+__dirname+'/mbtiles/tipp_out_'+ earthquake_unique_id + '.mbtiles', function(err, source) {
    if (err) {
        logger.error(err.message);
        throw err;
    }
    sources.set(earthquake_unique_id, source); 
    logger.info('Updated source! New tiles!');
});
}

Thank you.

I think that error from Nginx is indicating that the connection was closed by your nodejs server (i.e., "upstream"). How is nodejs configured?