The Modulus images are a set of Docker images designed to run arbitrary applications with a standardized external interface. The Modulus image convention enforces a high degree of security and control required by PaaS environments and might not be suitable for small, more focused, deployments.
The Modulus base image creates a mop user, under which all external software is run. The mop user does not have write access to anywhere on the Docker volume. Instead it can only write to a volume externally mounted from the host system.
/mnt
The volume mounted at /mnt requires the follow subdirectories to be created by the host system and accessible by the mop user/group.
/mnt/tmpTemporary storage. The TEMP_DIR environment variable is defined to here./mnt/homeThe mop user's home directory. The HOME environment variable is defined to here./mnt/logApplication stdout/stderr is placed in this directory with the filenameapp.log./mnt/appThe application itself is placed in this directory./mnt/notificationsCrash and other notifications, generated by supervisor, are placed here./mnt/app-storagePersistent storage is mounted here. It's also mounted to /app-storage at runtime./mnt/supervisor.confThe supervisor daemon is run with this configuration file.
The Modulus run image standard requires there to be an executable somewhere in the PATH named start. This executable should not block and should redirect any logging to stdout. In most Modulus run images the start script does much more than simply run the customer application. For example in the Node.js run image it is also responsible for reading the package.json and initilializing the correct version of Node.js.
Modulus makes use of Supervisor for process monitoring. The base run image provides a common supervisor configuration file that loads an application specific configuration file from /mnt/supervisor.conf. Modulus generates this file as a way to provide arbitrary environment variables and redirect stdout to /mnt/log/app.log. It also provides log rotation and crash notifications.
The base run image is not meant to be run directly. It's designed to be inherited by an application specific image, for example the Node.js run image.
FROM: onmodulus/run-base
# Customizations
# The base image extends phusion/baseimage so it's important to run
# the init system as the CMD.
CMD ["/sbin/my_init"]
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