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AWS Elastic Beanstalk
Developer Guide (API Version 2010-12-01)

Configuring the Application Process with a Procfile

To specify custom commands to start a Go application, include a file called Procfile at the root of your source bundle. The file name is case sensitive. Use the following format for the Procfile:

<process_name>: <command>

Each line in your Procfile must conform to the following regular expression: ^[A-Za-z0-9_]+:\s*.+$.

Elastic Beanstalk expects processes run from the Procfile to run continuously. Elastic Beanstalk monitors these applications and restarts any process that terminates. For short-running processes, use a Buildfile command.

You can use any name for your Go application, as long as it conforms to the aforementioned regular expression. You must call the main application web.

web: bin/server
queue_process: bin/queue_processor
foo: bin/fooapp

Elastic Beanstalk exposes the main web application on the root URL of the environment; for example, http://my-go-env.elasticbeanstalk.com.

Elastic Beanstalk configures the nginx proxy to forward requests to your application on the port number specified in the PORT environment variable for your application. Your application should always listen on that port. You can access this variable within your application by calling the os.Getenv("PORT") method.

Elastic Beanstalk uses the port number specified in the PORT option setting for the port for the first application in the Procfile, and then increments the port number for each subsequent application in the Procfile by 100. If the PORT option is not set, Elastic Beanstalk uses 5000 for the initial port.

In the preceding example, the PORT environment variable for the web application is 5000, the queue_process application is 5100, and the foo application is 5200.

You can specify the initial port by setting the PORT option with the aws:elasticbeanstalk:application:environment namespace, as shown in the following example.

option_settings:
  - namespace:  aws:elasticbeanstalk:application:environment
    option_name:  PORT
    value:  <first_port_number>

For more information about setting environment variables for your application, see Option Settings.

Elastic Beanstalk also runs any application whose name does not have the web_ prefix, but these applications are not available from outside of your instance.

Standard output and error streams from processes started with a Procfile are captured in log files named after the process and stored in /var/log. For example, the web process in the preceding example generates logs named web-1.log and web-1.error.log for stdout and stderr, respectively.

All paths in the Procfile are relative to the root of the source bundle. If you know in advance where the files reside on the instance, you can include absolute paths in the Procfile.