# Managing Application Processes Drycc Workflow manages your application as a set of processes that can be named, scaled and configured according to their role. This gives you the flexibility to easily manage the different facets of your application. For example, you may have web-facing processes that handle HTTP traffic, background worker processes that do async work, and a helper process that streams from the Twitter API. By using a Procfile, either checked in to your application or provided via the CLI you can specify the name of the type and the application command that should run. To spawn other process types, use `drycc scale =` to scale those types accordingly. ## Default Process Types In the absence of a Procfile, a single, default process type is assumed for each application. Applications built using [Buildpacks][buildpacks] via `git push` implicitly receive a `web` process type, which starts the application server. Rails 4, for example, has the following process type: web: bundle exec rails server -p $PORT All applications utilizing [Dockerfiles][dockerfile] have an implied `web` process type, which runs the Dockerfile's `CMD` directive unmodified: $ cat Dockerfile FROM centos:latest COPY . /app WORKDIR /app CMD python -m SimpleHTTPServer 5000 EXPOSE 5000 For the above Dockerfile-based application, the `web` process type would run the Container `CMD` of `python -m SimpleHTTPServer 5000`. Applications utilizing [remote Container images][container image], a `web` process type is also implied, and runs the `CMD` specified in the Container image. !!! note The `web` process type is special as they’is the default process type that will receive HTTP traffic from Workflow’s routers. Other process types can be named arbitrarily. ## Declaring Process Types If you use [Buildpack][buildpacks] or [Dockerfile][dockerfile] builds and want to override or specify additional process types, simply include a file named `Procfile` in the root of your application's source tree. The format of a `Procfile` is one process type per line, with each line containing the command to invoke: : The syntax is defined as: * `` – a lowercase alphanumeric string, is a name for your command, such as web, worker, urgentworker, clock, etc. * `` – a command line to launch the process, such as `rake jobs:work`. This example Procfile specifies two types, `web` and `sleeper`. The `web` process launches a web server on port 5000 and a simple process which sleeps for 900 seconds and exits. ``` $ cat Procfile web: bundle exec ruby web.rb -p ${PORT:-5000} sleeper: sleep 900 ``` If you are using [remote Container images][container image], you may define process types by either running `drycc pull` with a `Procfile` in your working directory, or by passing a stringified Procfile to the `--procfile` CLI option. For example, passing process types inline: ``` $ drycc pull drycc/example-go:latest --procfile="web: /app/bin/boot" ``` Read a `Procfile` in another directory: ``` $ drycc pull drycc/example-go:latest --procfile="$(cat deploy/Procfile)" ``` Or via a Procfile located in your current, working directory: ``` $ cat Procfile web: /bin/boot sleeper: echo "sleeping"; sleep 900 $ drycc pull -a steely-mainsail drycc/example-go Creating build... done $ drycc scale sleeper=1 -a steely-mainsail Scaling processes... but first, coffee! done in 0s NAME RELEASE STATE TYPE STARTED steely-mainsail-sleeper-76c45b967c-4qm6w v3 up sleeper 2023-12-08T02:25:00UTC steely-mainsail-web-c4f44c4b4-7p7dh v3 up web 2023-12-08T02:25:00UTC ``` !!! note Only process types of `web` will be scaled to 1 automatically. If you have additional process types remember to scale the process counts after creation. To remove a process type simply scale it to 0: ``` $ drycc scale sleeper=0 -a steely-mainsail Scaling processes... but first, coffee! done in 3s NAME RELEASE STATE TYPE STARTED steely-mainsail-web-c4f44c4b4-7p7dh v3 up web 2023-12-08T02:25:00UTC ``` ## Scaling Processes Applications deployed on Drycc Workflow scale out via the [process model][]. Use `drycc scale` to control the number of [containers][container] that power your app. ``` $ drycc scale web=5 -a iciest-waggoner Scaling processes... but first, coffee! done in 3s NAME RELEASE STATE TYPE STARTED iciest-waggoner-web-c4f44c4b4-7p7dh v3 up web 2023-12-08T02:25:00UTC iciest-waggoner-web-c4f44c4b4-8p7dh v3 up web 2023-12-08T02:25:00UTC iciest-waggoner-web-c4f44c4b4-9p7dh v3 up web 2023-12-08T02:25:00UTC iciest-waggoner-web-c4f44c4b4-1p7dh v3 up web 2023-12-08T02:25:00UTC iciest-waggoner-web-c4f44c4b4-2p7dh v3 up web 2023-12-08T02:25:00UTC ``` If you have multiple process types for your application you may scale the process count for each type separately. For example, this allows you to manage web process independently from background workers. For more information on process types see our documentation for [Managing App Processes](managing-app-processes.md). In this example, we are scaling the process type `web` to 5 but leaving the process type `background` with one worker. ``` $ drycc scale web=5 Scaling processes... but first, coffee! done in 4s NAME RELEASE STATE TYPE STARTED scenic-icehouse-web-3291896318-7lord v3 up web 2023-12-08T02:25:00UTC scenic-icehouse-web-3291896318-jn957 v3 up web 2023-12-08T02:25:00UTC scenic-icehouse-web-3291896318-rsekj v3 up web 2023-12-08T02:25:00UTC scenic-icehouse-web-3291896318-vwhnh v3 up web 2023-12-08T02:25:00UTC scenic-icehouse-web-3291896318-vokg7 v3 up web 2023-12-08T02:25:00UTC scenic-icehouse-web-3291896318-vokg7 v3 up web 2023-12-08T02:25:00UTC scenic-icehouse-background-3291896318-yf8kh v3 up web 2023-12-08T02:25:00UTC ``` Scaling a process down, by reducing the process count, sends a `TERM` signal to the processes, followed by a `SIGKILL` if they have not exited within 30 seconds. Depending on your application, scaling down may interrupt long-running HTTP client connections. For example, scaling from 5 processes to 3: ``` $ drycc scale web=3 Scaling processes... but first, coffee! done in 1s NAME RELEASE STATE TYPE STARTED scenic-icehouse-web-3291896318-vwhnh v2 up web 2023-12-08T02:25:00UTC scenic-icehouse-web-3291896318-vokg7 v2 up web 2023-12-08T02:25:00UTC scenic-icehouse-web-3291896318-vokg9 v2 up web 2023-12-08T02:25:00UTC scenic-icehouse-background-3291896318-yf8kh v2 up web 2023-12-08T02:25:00UTC ``` ## Get a Shell to a Running Container Verify that the container is running: ``` # drycc ps NAME RELEASE STATE TYPE STARTED python-getting-started-web-69b7d4bfdc-kl4xf v2 up web 2023-12-08T02:25:00UTC === python-getting-started Processes --- web: python-getting-started-web-69b7d4bfdc-kl4xf up (v2) ``` Get a shell to the running container: ``` # drycc ps:exec python-getting-started-web-69b7d4bfdc-kl4xf -it -- bash ``` In your shell, list the root directory: ``` # Run this inside the container ls / ``` Running individual commands in a container ``` # drycc ps:exec python-getting-started-web-69b7d4bfdc-kl4xf -- date ``` Use "drycc ps --help" for a list of global command-line (applies to all commands). ## Autoscale Autoscale allows adding a minimum and maximum number of pods on a per process type basis. This is accomplished by specifying a target CPU usage across all available pods. This feature is built on top of [Horizontal Pod Autoscaling][HPA] in Kubernetes or [HPA][] for short. !!! note This is an alpha feature. It is recommended to be on the latest Kubernetes when using this feature. ``` $ drycc autoscale:set web --min=3 --max=8 --cpu-percent=75 Applying autoscale settings for process type web on scenic-icehouse... done ``` And then review the scaling rule that was created for `web` ``` $ drycc autoscale:list UUID TYPE PERCENT MIN MAX e916b333-53c1-4d4c-ac5a-23e6961fb544 web 75 3 8 ``` Remove scaling rule ``` $ drycc autoscale:unset web Removing autoscale for process type web on scenic-icehouse... done ``` For autoscaling to work CPU requests have to be specified on each application Pod (can be done via `drycc limits --cpu`). This allows the autoscale policies to do the [appropriate calculations][autoscale-algo] and make decisions on when to scale up and down. Scale up can only happen if there was no rescaling within the last 3 minutes. Scale down will wait for 5 minutes from the last rescaling. That information and more can be found at [HPA algorithm page][autoscale-algo]. ## Restarting an Application Processes If you need to restart an application process, you may use `drycc ps:restart`. Behind the scenes, Drycc Workflow instructs Kubernetes to terminate the old process and launch a new one in its place. ``` $ drycc ps NAME RELEASE STATE TYPE STARTED scenic-icehouse-web-3291896318-vokg7 v2 up web 2023-12-08T02:25:00UTC scenic-icehouse-web-3291896318-rsekj v2 up web 2023-12-08T02:50:21UTC scenic-icehouse-web-3291896318-vokg7 v2 up web 2023-12-08T02:25:00UTC scenic-icehouse-background-3291896318-yf8kh v2 up web 2023-12-08T02:25:00UTC $ drycc ps:restart scenic-icehouse-background-3291896318-yf8kh NAME RELEASE STATE TYPE STARTED scenic-icehouse-web-3291896318-vokg7 v2 up web 2023-12-08T02:25:00UTC scenic-icehouse-web-3291896318-rsekj v2 up web 2023-12-08T02:50:21UTC scenic-icehouse-web-3291896318-vokg7 v2 up web 2023-12-08T02:25:00UTC scenic-icehouse-background-3291896318-yf8kh v2 starting web 2023-12-08T02:25:00UTC ``` Notice that the process name has changed from `scenic-icehouse-background-3291896318-yf8kh` to `scenic-icehouse-background-3291896318-yd87g`. In a multi-node Kubernetes cluster, this may also have the effect of scheduling the Pod to a new node. [container]: ../reference-guide/terms.md#container [process model]: https://devcenter.heroku.com/articles/process-model [buildpacks]: ../applications/using-buildpacks.md [dockerfile]: ../applications/using-dockerfiles.md [container image]: ../applications/using-container-images.md [HPA]: https://kubernetes.io/docs/tasks/run-application/horizontal-pod-autoscale/ [autoscale-algo]: https://github.com/kubernetes/community/blob/master/contributors/design-proposals/horizontal-pod-autoscaler.md#autoscaling-algorithm