My application boot time is slow and leaves the app unavailable during dyno restarts.
For zero downtime deploys and restarts we recommend using Preboot https://devcenter.heroku.com/articles/preboot for Common Runtime apps. There are some apps that aren't compatible with Preboot so please be sure to check the documentation carefully.
It can also help to make sure that your
web process only runs commands that are necessary to start a web server. For example, any asset compilation or build steps (e.g.
webpack for Node apps) should be moved to the build phase. For Node JS applications specifically, we have some guidance on this here: https://devcenter.heroku.com/articles/node-best-practices#hook-things-up