![]() ![]() One example is using Ruby’s rack-timeout gem and setting the timeout value to lower than the router’s 30 second timeout, such as 15 seconds. In addition to server level timeouts you can use other request timeout libraries. The timer will begin once Unicorn starts processing the request, if 15 seconds pass, then the master process will send a SIGKILL to the worker but no exception will be raised. In Unicorn you can set a timeout in config/unicorn.rb like this: timeout 15 Subsequent requests may then be routed to the same process which will be unable to respond (depending on the concurrency behavior of the application’s language/framework) causing further degradation.ĭepending on your language you may be able to set a timeout on the app server level. The web dyno that was processing the request is left untouched – it will continue to process the request, even though it won’t be able to send any response. When a connection is terminated, an error page will be issued to the client. If the server keeps the connection open for 55 seconds without sending any data, you’ll see a request timeout. If you’re sending a streaming response, such as with server-sent events, you’ll need to detect when the client has hung up, and make sure your app server closes the connection promptly. If no data is sent during the 55 second window, the connection will be terminated. ![]() However, each byte transmitted thereafter (either received from the client or sent by your application) resets a rolling 55 second window. An application has an initial 30 second window to respond with a single byte back to the client. Heroku supports HTTP 1.1 features such as long-polling and streaming responses. This pattern frees your web processes up to do more work, and decreases overall application response times. If your server requires longer than 30 seconds to complete a given request, we recommend moving that work to a background task or worker to periodically ping your server to see if the processing request has been finished. ![]() You can read more about this below in Timeout behavior. Unlike the routing timeout, these timers will begin when the request begins being processed by your application. To avoid this situation Heroku recommends setting a timeout within your application and keeping the value well under 30 seconds, such as 10 or 15 seconds. While the router has returned a response to the client, your application will not know that the request it is processing has reached a time-out, and your application will continue to work on the request. When a timeout is detected the router will return a customizable error page to the client and an H12 error is emitted to your application logs. The request must then be processed in the dyno by your application, and a response delivered back to the router, within 30 seconds to avoid the timeout. The countdown for this 30 second timeout begins after the entire request (all request headers and, if applicable, the request body) has been sent from the router to the dyno. When this happens the router will terminate the request if it takes longer than 30 seconds to complete. Occasionally a web request may hang or take an excessive amount of time to process by your application. Best practice is to get the response time of your web application to be under 500ms, this will free up the application for more requests and deliver a high quality user experience to your visitors. These requests are intended to be served by your application quickly. Web requests processed by Heroku are directed to your dynos via a number of Heroku routers. Learn more: Optimizing Dyno Usage and Preventing H12 Errors. Tuning your applications’ dynos may help to prevent timeouts and generally improve performance.
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