express-graceful-exit
A component in having zero downtime deploys for Node.js with Express. It was developed for Express 3.X, so it may need work to be compatible with Express 2.X
This module was originally developed for Frafty, a Daily Fantasy Sports site.
Installation
$ cd /path/to/your/project
$ npm install express-graceful-exit
Compatibility
v0.X.X versions are backwards API compatible, with the caveate that process exit is called in a setTimeout
block from v0.2.0 forward, so the timing is slightly different between v0.1.0 to v0.2.x+.
Usage
The following two components must both be used to enable fully graceful exits.
middleware
This middleware should be the very first middleware that gets setup with your Express app.
var express = require('express');
var app = express();
var gracefulExit = require('express-graceful-exit');
app.use(gracefulExit.middleware(app));
gracefulExitHandler
This function tells express to accept no new requests and gracefully closes the http server. It can be attached to a signal, or used as a normal function call if another tool is used (such as naught).
// Example for naught
process.on('message', function(message) {
if (message === 'shutdown') {
gracefulExit.gracefulExitHandler(app, server, {
socketio: app.settings.socketio
});
}
});
Options
Middleware
There are no options available currently.
Exit Handler
The following options are available:
Option | Description | Default |
---|---|---|
log | Print status messages and errors to the logger | false |
logger | Function that accepts a string to output a log message | console.log |
callback | Optional function that is called with the exit status code once express has shutdown, gracefully or not Use in conjunction with exitProcess: false when the caller handles process shutdown |
no-op |
exitProcess | If true, the module calls process.exit() when express has shutdown, gracefully or not |
true |
exitDelay | Wait timer duration in the final internal callback (triggered either by gracefulExitHandler or the suicideTimeout) if exitProcess: true |
10ms |
suicideTimeout | How long to wait before giving up on graceful shutdown, then returns exit code of 1 | 2m 10s (130s) |
socketio | An instance of socket.io , used to close all open connections after timeout |
none |
force | Instructs the module to forcibly close sockets once the suicide timeout elapses. For this option to work you must call gracefulExit.init(server) when initializing the HTTP server |
false |
Details
To gracefully exit this module will do the following things:
- Close the http server so no new connections are accepted
- Mark that the server will gracefully exit, so if a connection that is using the Keep-Alive header is still active, it will be told to close the connection
The HTTP status code of 502 is returned, so nginx, ELB, etc will try again with a working server - If a socket.io instance is passed in the options, it enumerates all connected clients and disconnects them
The client should have code to reconnect on disconnect - Server fully disconnects or the hard exit timer runs
- Once all connected clients are disconnected, the exit handler returns
0
- OR If there are any remaining connections after
suicideTimeout
ms, the handler returns1
- Once all connected clients are disconnected, the exit handler returns
- In either case, if exitProcess is set to true the exit handler waits exitDelay ms and calls
process.exit
Zero Downtime Deploys
This module does not give you zero downtime deploys on its own. It enables the http server to exit gracefully, which when used with a module like naught can provide zero downtime deploys.