Every time an application is redeployed on Porter (through a Github action, configuration change, etc), a new set of application instances will replace the old application instances. While your existing instances will not be replaced until the new instances are up and running, there is no way to guarantee that the process inside the application instance is up and running before the original instances are replaced. Health checks can be configured to prevent any downtime during deployment updates:. When your Web service is configured with health checks, Porter will ensure that no traffic is routed to your service unless the specified endpoints return a 200 status code. Health checks can be configured in the Advanced tab: Health Check Configuration For example, in the screenshot above, no traffic will be routed to the web service until the /healthz endpoint returns a 200 status code. This is useful for Zero Downtime Deployments. When you push a new update to your application, the old version of your application will not be spun down until the new version passes all health checks.