dguardado/Procfile

## README.md

      
    Raw
  

              README.md
            
          
    Starting an app with a shell script in Elastic Beanstalk

Situation


You need to use some environment variables in the command called by the Procfile used to start your app,
but environment variables are not supported in the Procfile
Naturally, you move the command into a shell script where the environment variables are accessible
Now, any time you restart the app (deploys, etc), the running application no longer shuts down,
and the new app process cannot start. You see a spew of messages in the logs about being unable to bind
to the application port because it is already used.

Solution

You should prefix your app launch command inside your shell script with the exec command. So if your app
launch command is my_server config.yaml, you should rewrite it to exec my_server config.yaml
Why this works

When stopping/restarting the application, Beanstalk will send kill signals to the process specified to in the Procfile.
However, when we launch the application with a shell script, our app is spawned as a child process. The original
script process now receives the kill signals, but our app never hears those signals and keeps running.
eg

PID: 123 - start_server.sh <-- receives kill signals

PID: 124 - my_server <-- does not receive kill signals


Prefixing the command with exec makes it so our app will take over the original process of the script, including PID,
environment, etc. When this happens, OUR app will receive the kill signals.

PID: 123 - start_server.sh ==> (exec) my_server <-- our app takes over the original process, and now receives kill signals

Scope

This issue affects the AWS Elastic Beanstalk Java platform, and the fix has been demonstrated to work on that platform.
It may also affect the Go platform, and the fix may work there but has not been verified. I am not sure if this problem
is relevant to other beanstalk platforms.

  
## Procfile
web: ./start_server.sh # would like to use environment variables here, but it is not supported

## start_server.sh
#!/bin/bash

# We want to use environment variables here, but can't use them in the procfile
JAVA_OPTS="-Xmx768m -XX:+HeapDumpOnOutOfMemoryError -XX:-OmitStackTraceInFastThrow -XX:MaxJavaStackTraceDepth=-1 -Dnewrelic.environment=$MONITOR_ENV -javaagent:$PWD/newrelic.jar"

# exec here will make our application take over the process of this shell script
exec java $JAVA_OPTS -jar app.jar server config.yaml
	#!/bin/bash

	# We want to use environment variables here, but can't use them in the procfile
	JAVA_OPTS="-Xmx768m -XX:+HeapDumpOnOutOfMemoryError -XX:-OmitStackTraceInFastThrow -XX:MaxJavaStackTraceDepth=-1 -Dnewrelic.environment=$MONITOR_ENV -javaagent:$PWD/newrelic.jar"

	# exec here will make our application take over the process of this shell script
	exec java $JAVA_OPTS -jar app.jar server config.yaml