Access environment variables passed in docker run from supervisor child process - docker

Question

I'm running a docker container with the following command:
docker run -it -e CustomEnvVariable="val123" -p 80:80 imagename
The image has supervisor running with the following conf file for my app:
[program:myapp]
command=/usr/bin/dotnet /root/myapp/myapp.dll
directory=/root/myapp/
autostart=true
autorestart=true
stderr_logfile=/var/log/myapp.err.log
stdout_logfile=/var/log/myapp.out.log
environment=ASPNETCORE__ENVIRONMENT=Production
stopsignal=INT
user=root
How can I access CustomEnvVariable from within myapp after supervisor launches it?
I tried the following value in the conf file environment value:
environment=ASPNETCORE__ENVIRONMENT=Production,CustomEnvVariable=%(ENV_CustomEnvVariable)s
but I would received this error when restarting supervisor:
Restarting supervisor: Error:
Format string 'ASPNETCORE__ENVIRONMENT=Production,CustomEnvVariable="%(ENV_CustomEnvVariable)s"'
for 'environment' contains names which cannot be expanded
Some more information:
Using supervisor version: 3.0 (install via apt-get install supervisor -y).
I confirmed that the value of CustomEnvVariable is reaching the container by checking the output of echo $CustomEnvVariable.
I did a quick scan of all the environment variables available to from the app, here are the results:
{
"LC_ADDRESS": "",
"SUPERVISOR_PROCESS_NAME": "myapp",
"LC_MONETARY": "",
"LC_MESSAGES": "",
"LC_NAME": "",
"SUPERVISOR_ENABLED": "1",
"SUPERVISOR_SERVER_URL": "unix:///var/run/supervisor.sock",
"LC_COLLATE": "",
"ASPNETCORE__ENVIRONMENT": "Production",
"SUPERVISOR_GROUP_NAME": "myapp",
"LANG": "",
"LC_NUMERIC": "",
"LANGUAGE": "",
"LC_PAPER": "",
"LC_IDENTIFICATION": "",
"LC_CTYPE": "",
"LC_MEASUREMENT": "",
"TERM": "xterm",
"LC_TIME": "",
"LC_ALL": "",
"PATH": "/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin",
"LC_TELEPHONE": "",
"PWD": "/"
}

Answer 1

The syntax is correct, but environment expansion is only available in version > 3.2 of supervisor, as per this github issue.