Process Types and the Procfile¶

A Procfile is a mechanism for declaring what commands are run by your application’s containers on the Deis platform. It follows the process model. You can use a Procfile to declare various process types, such as multiple types of workers, a singleton process like a clock, or a consumer of the Twitter streaming API.

Process Types as Templates¶

A Procfile is a text file named Procfile placed in the root of your application that lists the process types in an application. Each process type is a declaration of a command that is executed when a container of that process type is started.

All the language and frameworks using Heroku’s Buildpacks declare a web process type, which starts the application server. Rails 3 has the following process type:

web: bundle exec rails server -p $PORT

All applications using Dockerfile deployments have an implied cmd process type, which spawns the default process of a Docker image:

$ cat Dockerfile
FROM centos:latest
COPY . /app
WORKDIR /app
CMD python -m SimpleHTTPServer 5000
EXPOSE 5000

For applications using Docker image deployments, a cmd process type is also implied and spawns the default process of the image.

Declaring Process Types¶

Process types are declared via a file named Procfile, placed in the root of your app. Its format is one process type per line, with each line containing:

<process type>: <command>

The syntax is defined as:

<process type> – an 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.

Note

The web and cmd process types are special as they’re the only process types that will receive HTTP traffic from Deis’s routers. Other process types can be named arbitrarily.

Deploying to Deis¶

A Procfile is not necessary to deploy most languages supported by Deis. The platform automatically detects the language and supplies a default web process type to boot the server.

Creating an explicit Procfile is recommended for greater control and flexibility over your app.

For Deis to use your Procfile, add the Procfile to the root of your application, then push to Deis:

$ git add .
$ git commit -m "Procfile"
$ git push deis master
...
-----> Procfile declares process types: web, worker
Compiled slug size is 10.4MB

       Launching... done, v2

-----> unisex-huntress deployed to Deis
       http://unisex-huntress.example.com

For Docker image deployments, a Procfile in the current directory or specified by deis pull --procfile will define the default process types for the application.

Use deis scale web=3 to increase web processes to 3, for example. Scaling a process type directly changes the number of Containers running that process.

Web vs Cmd Process Types¶

When deploying to Deis using a Heroku Buildpack, Deis boots the web process type to boot the application server. When you deploy an application that has a Dockerfile or uses Docker images, Deis boots the cmd process type. Both act similarly in that they are exposed to the router as web applications. However, The cmd process type is special because it is equivalent to running the Container without any additional arguments. Every other process type is equivalent to running the relevant command that is provided in the Procfile.

When migrating from Heroku Buildpacks to a Docker-based deployment, Deis will not convert web process types to cmd. To do this, you’ll have to manually scale down the old process type and scale the new process type up.