Your likings, read the comments-they’re quite good. Usually located at /etc/nginx/nf, so place it there, and tweak it to We’ll grab the nf exampleĬonfiguration shipped with Unicorn, the nginx configuration file is Start by installing nginx via your favorite package manager. We’re going to set up nginx in front of Unicorn. Without any significant speed drop since children are slowly restarted. Github has shared their init for Unicorn, which sends the appropriate signalsĪccording to the spec for various actions. Unicorn’s signal handling is described here. #Run rails unicorn https upgradeWe can also use this process to upgrade Unicorn itself. So nginx doesn’t have to even care about the transition. Without any downtime: the old and new workers all share the Unix Domain Socket Have a fresh version of our app, fully loaded and ready to receive requests, Once all the workers have finished serving requests, it dies. When the old master receives the QUIT, it starts gracefully shutting down its The first workerįorked notices there is still an old master and sends it a QUIT signal. Master is fully loaded it forks all the workers it needs. This tells it toīegin starting a new master process, reloading all our app code. The Unicorn master and worker processes respond to Unix signals.įirst we send the existing Unicorn master a USR2 SIGNAL. You can upgrade Unicorn, your entire application, libraries and even your Ruby interpreter without dropping clients. With Unicorn one can deploy with zero downtime. Instead, you willīe taken off the long queue quickly and slow requests will fail in isolation. Were unlucky enough to end up behind a slow request.īecause of Unicorn’s long queue model, this will not happen. Easily, a lot ofįast requests can end up behind slow requests, because they are distributedĮssentially randomly, which means your request can timeout simply because you To push the request, you have many short queues at each worker. In the conventional web server using the busyness heuristic to determine where Presented with an adorable whale just because you landed in the wrong queue atĪnd then they continue to talk about supermarket queues, read the whole thing. Individual worker’s line gets too long, we have to drop requests. Unusually long, and everyone waiting behind that request suffers. Quickly, but large systems have outliers. This is unnoticeable to users when the queue is short and we handle requests Welcome to Unicorn’s world of evented I/O: We respond by putting those requests in a queue. Their blog post on why they moved to Unicorn:Įvery server has a fixed number of workers that handle incoming requests.ĭuring peak hours, we may get more simultaneous requests than available Twitter has shed some light on this issue in This solves the problems mentioned above. Thus requests are always handled by a worker which can handle request Requests are initially queued at the master on a Unix socket, workersĪccept(2) (pull) requests off the queue (shared Unix socket) when they are Unicorn solves this problem with a pull-model rather than a push-model. The common load balancer does not account for this, queueing clients at
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