Managing App Processes
8 minute read
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 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 an API.
By using a Procfile, either checked into your application or provided via the CLI, you can specify the name of the process type and the application command that should run. To spawn other process types, use drycc scale <ptype>=<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
Theweb process type is special as it 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 asrake 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 PTYPE READY RESTARTS STARTED
steely-mainsail-sleeper-76c45b967c-4qm6w v3 up sleeper 1/1 0 2023-12-08T02:25:00UTC
steely-mainsail-web-c4f44c4b4-7p7dh v3 up web 1/1 0 2023-12-08T02:25:00UTC
Note
Only process types ofweb 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 PTYPE READY RESTARTS STARTED
steely-mainsail-web-c4f44c4b4-7p7dh v3 up web 1/1 0 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 PTYPE READY RESTARTS STARTED
iciest-waggoner-web-c4f44c4b4-7p7dh v3 up web 1/1 0 2023-12-08T02:25:00UTC
iciest-waggoner-web-c4f44c4b4-8p7dh v3 up web 1/1 0 2023-12-08T02:25:00UTC
iciest-waggoner-web-c4f44c4b4-9p7dh v3 up web 1/1 0 2023-12-08T02:25:00UTC
iciest-waggoner-web-c4f44c4b4-1p7dh v3 up web 1/1 0 2023-12-08T02:25:00UTC
iciest-waggoner-web-c4f44c4b4-2p7dh v3 up web 1/1 0 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 processes 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 PTYPE READY RESTARTS STARTED
scenic-icehouse-web-3291896318-7lord v3 up web 1/1 0 2023-12-08T02:25:00UTC
scenic-icehouse-web-3291896318-jn957 v3 up web 1/1 0 2023-12-08T02:25:00UTC
scenic-icehouse-web-3291896318-rsekj v3 up web 1/1 0 2023-12-08T02:25:00UTC
scenic-icehouse-web-3291896318-vwhnh v3 up web 1/1 0 2023-12-08T02:25:00UTC
scenic-icehouse-web-3291896318-vokg7 v3 up web 1/1 0 2023-12-08T02:25:00UTC
scenic-icehouse-web-3291896318-vokg7 v3 up web 1/1 0 2023-12-08T02:25:00UTC
scenic-icehouse-background-3291896318-yf8kh v3 up background 1/1 0 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 PTYPE READY RESTARTS STARTED
scenic-icehouse-web-3291896318-vwhnh v2 up web 1/1 0 2023-12-08T02:25:00UTC
scenic-icehouse-web-3291896318-vokg7 v2 up web 1/1 0 2023-12-08T02:25:00UTC
scenic-icehouse-web-3291896318-vokg9 v2 up web 1/1 0 2023-12-08T02:25:00UTC
scenic-icehouse-background-3291896318-yf8kh v2 up background 1/1 0 2023-12-08T02:25:00UTC
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
PTYPE PERCENT MIN MAX
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.
Fetch Container Logs
List the containers:
$ drycc ps
NAME RELEASE STATE PTYPE READY RESTARTS STARTED
python-getting-started-web-69b7d4bfdc-kl4xf v2 up web 1/1 0 2023-12-08T02:25:00UTC
=== python-getting-started Processes
--- web:
python-getting-started-web-69b7d4bfdc-kl4xf up (v2)
Fetch the container logs:
$ drycc ps logs -f python-getting-started-web-69b7d4bfdc-kl4xf
[2024-05-24 07:14:39 +0000] [1] [INFO] Starting gunicorn 20.1.0
[2024-05-24 07:14:39 +0000] [1] [INFO] Listening at: http://0.0.0.0:8000 (1)
[2024-05-24 07:14:39 +0000] [1] [INFO] Using worker: gevent
[2024-05-24 07:14:39 +0000] [8] [INFO] Booting worker with pid: 8
[2024-05-24 07:14:39 +0000] [9] [INFO] Booting worker with pid: 9
[2024-05-24 07:14:39 +0000] [10] [INFO] Booting worker with pid: 10
[2024-05-24 07:14:39 +0000] [11] [INFO] Booting worker with pid: 11
Get Container Information
List the containers:
$ drycc ps describe python-getting-started-web-69b7d4bfdc-kl4xf
Container: python-getting-started-web
Image: drycc/python-getting-started:latest
Command:
Args:
- gunicorn
- -c
- gunicorn_config.py
- helloworld.wsgi:application
State: running
startedAt: "2024-05-24T07:14:39Z"
Ready: true
Restart Count: 0
Delete a Container
Delete the containers. Due to the set number of replicas, a new container will be launched to meet the quantity requirement.
$ drycc ps delete python-getting-started-web-69b7d4bfdc-kl4xf
Deleting python-getting-started-web-69b7d4bfdc-kl4xf from python-getting-started... done
Get a Shell to a Running Container
Verify that the container is running:
$ drycc ps
NAME RELEASE STATE PTYPE READY RESTARTS STARTED
python-getting-started-web-69b7d4bfdc-kl4xf v2 up web 1/1 0 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 options (applies to all commands).
Restarting 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 PTYPE READY RESTARTS STARTED
scenic-icehouse-web-3291896318-vokg7 v2 up web 1/1 0 2023-12-08T02:25:00UTC
scenic-icehouse-web-3291896318-rsekj v2 up web 1/1 0 2023-12-08T02:50:21UTC
scenic-icehouse-web-3291896318-vokg7 v2 up web 1/1 0 2023-12-08T02:25:00UTC
scenic-icehouse-background-3291896318-yf8kh v2 up background 1/1 0 2023-12-08T02:25:00UTC
$ drycc ps restart scenic-icehouse-background
NAME RELEASE STATE PTYPE READY RESTARTS STARTED
scenic-icehouse-web-3291896318-vokg7 v2 up web 1/1 0 2023-12-08T02:25:00UTC
scenic-icehouse-web-3291896318-rsekj v2 up web 1/1 0 2023-12-08T02:50:21UTC
scenic-icehouse-web-3291896318-vokg7 v2 up web 1/1 0 2023-12-08T02:25:00UTC
scenic-icehouse-background-3291896318-yf8kh v2 starting background 1/1 0 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.
Use “drycc ps –help” for a list of ps command-line options (process info).
List Application Process Types
$ drycc pts
NAME RELEASE READY UP-TO-DATE AVAILABLE GARBAGE STARTED
web v2 3/3 1 1 true 2023-12-08T02:25:00UTC
background v2 1/1 1 1 false 2023-12-08T02:25:00UTC
Clean Process Types
Clean up non-existent process types; it is usually executed automatically when autodeploy is set to true.
$ drycc pts clean background
Get Deployment Info of Application Process Type
$ drycc pts describe web
Container: python-getting-started-web
Image: drycc/python-getting-started:latest
Command:
Args:
- gunicorn
- -c
- gunicorn_config.py
- helloworld.wsgi:application
Limits:
cpu 1
ephemeral-storage 2Gi
memory 1Gi
Liveness: http-get headers=[] path=/geo/ port=8000 delay=120s timeout=10s period=20s #success=1 #failure=3
Readiness: http-get headers=[] path=/geo/ port=8000 delay=120s timeout=10s period=20s #success=1 #failure=3
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