Using the NGINX JavaScript Module to Progressively Transition Clients to a New Server

progressive_transition.conf

upstream old {
    server 10.0.0.1;
    server 10.0.0.2;
}

upstream new {
    server 10.0.0.9;
    server 10.0.0.10;
}

js_import /etc/nginx/progressive_transition.js;
js_set $upstream progressive_transition.transitionStatus; # Returns "old|new" based on window pos

server {
    listen 80;

    location / {
        set $transition_window_start "Wed, 31 Aug 2016 17:00:00 +0100";
        set $transition_window_end   "Wed, 31 Aug 2016 19:00:00 +0100";

        proxy_pass http://$upstream;
        error_log /var/log/nginx/transition.log info; # Enable NJS logging
    }
}

# vim: syntax=nginx

progressive_transition.js

function fnv32a(str) {
  var hval = 2166136261;
  for (var i = 0; i < str.length; ++i ) {
    hval ^= str.charCodeAt(i);
    hval += (hval << 1) + (hval << 4) + (hval << 7) + (hval << 8) + (hval << 24);
  }
  return hval >>> 0;
}

function transitionStatus(req) {
  var vars, window_start, window_end, time_now, timepos, numhash, hashpos;

  // Get the transition window from NGINX configuration
  vars = req.variables;
  window_start = new Date(vars.transition_window_start);
  window_end = new Date(vars.transition_window_end);

  // Are we in the transition time window?
  time_now = Date.now();
  if ( time_now < window_start ) {
    return "old";
  } else if ( time_now > window_end ) {
    return "new";
  } else { // We are in the transition window
    // Calculate our position in the window (0-1)
    timepos = (time_now - window_start) / (window_end - window_start);

    // Get numeric hash for this client's IP address
    numhash = fnv32a(req.remoteAddress);

    // Calculate the hash's position in the output range (0-1)
    hashpos = numhash / 4294967295; // Upper bound is 32 bits
    req.log("timepos = " + timepos + ", hashpos = " + hashpos); //error_log [info]

    // Should we transition this client?
    if ( timepos > hashpos ) {
      return "new";
    } else {
      return "old";
    }
  }
}

export default { transitionStatus }

For a discussion of these files, see Using the NGINX JavaScript Module to Progressively Transition Clients to a New Server