Modulus Base Docker Runtime Image

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 mop user

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.

Volumes

/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/tmp Temporary storage. The TEMP_DIR environment variable is defined to here.
/mnt/home The mop user's home directory. The HOME environment variable is defined to here.
/mnt/log Application stdout/stderr is placed in this directory with the filename app.log.
/mnt/app The application itself is placed in this directory.
/mnt/notifications Crash and other notifications, generated by supervisor, are placed here.
/mnt/app-storage Persistent storage is mounted here. It's also mounted to /app-storage at runtime.
/mnt/supervisor.conf The supervisor daemon is run with this configuration file.

The Start script

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.

Supervisor

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.

Usage

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"]

License

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.