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 <type>=<n> 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 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 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, 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 or 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:

<process type>: <command>

The syntax is defined as:

• <process type> – a lowercase alphanumeric string, is a name for your command, such as web, worker, urgentworker, clock, etc.
• <command> – 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, 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 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.

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 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 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.

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.