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Customization(5) | Geodesic
Nuru
March 2019

NAME

Customization - How to customize Geodesic at launch time

SYNOPSIS

Several features of Geodesic can be customized at launch time (rather than during the build of the Docker image) so that people can share an image yet still have things set up the way they like. This document describes how to configure the customization.

DESCRIPTION

A great deal of customization can be implemented by placing shell scripts on the host computer, to be read either at the start of bash profile script processing or at the end of it. These shell scripts can set up environment variables, command aliases, shell functions, etc. and through setting environment variables, can cause Geodesic to enable or disable certain features.

Due to technical limitations, there are a small number of options that can only be controlled via command line options or corresponding (exported) shell environment variables set in the user's shell before launching Geodesic via the wrapper script (which is the default and recommended way to launch Geodesic).

Users can also choose whether to have a single bash history file for all containers or to have separate history files.

Command line options (also environment variables)

Geodesic accepts a small number of command line options, which can also be set by corresponding (exported) shell environment variables. In all cases, the command line options must be introduced with double dashes and be set via =. Boolean options can be set =true with no argument on the command line. Command line options are lower case with words separated by dashes, while environment variables are upper case with words separated by underscores.

Valid:

geodesic --env-file=~/.geodesic/extra-envs
ENV_FILE=~/.geodesic/extra_envs geodesic
geodesic --geodesic-host-bindfs-enabled

Not valid:

geodesic --env-file ~/.geodesic/extra-envs
env-file=~/.geodesic/extra-envs
ENV-FILE=~/.geodesic/extra-envs
GEODESIC_HOST_BINDFS_ENABLED= geodesic

At the moment, underscores are accepted instead of dashes in command line arguments, but this behavior should not be relied on:

Works, but not officially supported:

geodesic --env-file=~/.geodesic/extra_envs

TODO: Document all the command line options in geodesic(1)

Root directory for configuration

All configuration files are stored under $GEODESIC_CONFIG_HOME, which defaults to /localhost/.geodesic. At this time, /localhost is mapped to the host $HOME directory and this cannot be configured yet, so all configuration files must be under $HOME, but within that limitation they can be placed anywhere. So if you set $GEODESIC_CONFIG_HOME to /localhost/work/config/geodesic, then files would go in ~/work/config/geodesic/ and below on your Docker host machine.

Resources

There are currently 5 Resources used for configuration:

  • Preferences, which are shell scripts loaded very early in the launch of the Geodesic shell.
  • Overrides, which are shell scripts loaded very late in the launch of the Geodesic shell.
  • bash history files, which store bash command line history.
  • A file of environment variable settings passed to docker --env-file
  • Command-line options (which can also be set by correspondingly named shell environment variables)

Additionally, when Geodesic exits normally, it will run the host command geodesic_on_exit if it is available. This is intended to be a script that you write and install anywhere on your PATH to do whatever cleanup you want. For example, change the window title.

Preferences and Overrides

Both preferences and overrides can be either a single file, named preferences and overrides respectively, or can be a collection of files in directories named preferences.d and overrides.d. If they are directories, all the visible files in the directories will be sourced, except for hidden files and files with names matching the GEODESIC_AUTO_LOAD_EXCLUSIONS regex, which defaults to (~|.bak|.log|.old|.orig|.disabled)$.

History files

bash history is always stored in a single file named history, never a directory of files nor files with any other name. If you want to use a separate history file for one Geodesic-based Docker image not shared by other Geodesic-based Docker images, you must create an empty history file in the image-specific configuration directory (see below).

Environment file

Geodesic passes a single argument to Docker's --env-file option when launching via the installed wrapper script. By default, that file is ~/.geodesic/env but that file name can be set via the --geodesic-default-env-file command line option or the GEODESIC_DEFAULT_ENV_FILE environment variable.

A second environment file can be specified in addition to the default via the --env-file command line option or ENV_FILE

Configuration by file placement

Resources can be in several places, and will be loaded from most general to most specific, according to the name of the docker container image.

  • The most general resources are the ones directly in $GEODESIC_CONFIG_HOME. These are applied first. To keep the top-level directory less cluttered and to avoid name clashes, you can put them in a subdirectory named defaults. If that subdirectory exists, then GEODESIC_CONFIG_HOME itself is not searched.
  • The DOCKER_IMAGE name is then parsed. Everything before the final / is considered the "company" name and everything after is, following the Cloudposse reference architecture, referred to as the "stage" name. So for the DOCKER_IMAGE name cloudposse/geodesic, the company name is cloudposse and the stage name is geodesic
  • The next place searched for resources is the directory with the same name as the "company". In our example, that would be ~/.geodesic/cloudposse. Resources here would apply to all containers from the same company.
  • The next place searched for resources is the directory with the same name as the "stage", which is generally the name of the project. In our example, that would be ~/.geodesic/geodesic. Resources here would apply to all containers with the same base name, perhaps various forks of the same project.
  • The final place searched is the directory with the full name of the Docker image: $GEODESIC_CONFIG_HOME/$DOCKER_IMAGE, i.e. ~/.geodesic/cloudposse/geodesic. Files here are the most specific to this container.

By loading them in this order, you can put your defaults at one level and then override/customize them at another, minimizing the amount of duplication needed to customize a wide range of containers.

Usage details

Preferences and Overrides are loaded in the order specified above and all that are found are loaded. For history files, only the last one found is used. To start keeping separate history, just create an empty history file in the appropriate place.

While Preferences and Override files themselves must be bash scripts and will be directly loaded into the top-level Geodesic shell, they can of course call other programs. You can even use them to pull configurations out of other places.

Symbolic links must be relative if you want them to work both inside Geodesic and outside of it. Symbolic links that reference directories that are not below $HOME on the host will not work.

When possible, Geodesic mounts the host $HOME directory as /localhost and creates a symbolic link from $HOME to /localhost so that files under $HOME on the host can be referenced by the exact same absolute path both on the host computer and inside Geodesic. For example, if the host $HOME is /Users/fred, then /Users/fred/src/example.sh will refer to the same file both on the host and from inside the Geodesic shell.

In general, you should put most of your customization in the Preferences files. Geodesic (usually) takes care to respect and adapt to preferences set before it starts adding on top of them. The primary use for overrides is if you need the results of the initialization process as inputs to your configuration, or if you need to undo something Geodesic does not yet provide a configuration option for not doing in the first place.

WARNING

One of the key benefits of Geodesic is that it provides a consistent environment for all users regardless of their local machine. It eliminates the "it works on my machine" excuse. While these customization options can be great productivity enhancements as well as provide the opportunity to install new features to try them out before committing to installing them permanently, they can also create the kind of divergence in environments that brings back the "it works on my machine" problem.

Therefore, we have included an option to disable the customization files: the preferences, the overrides, and the docker environment files. Simply set and export the host environment variable $GEODESIC_CUSTOMIZATION_DISABLED to any value other than "false" before launching Geodesic.

TROUBLESHOOTING

If customizations are not being found or are not working as expected, you can set the host environment variable $GEODESIC_TRACE to "custom" before launching Geodesic and a trace of the customization process will be output to the console.