pyentrypoint

pyentrypoint is a tool written in Python to manager Docker containers ENTRYPOINT.

This tool avoids writing shell scripts to:

• Handle commands and sub commands
• Identify linked containers
• Generate configuration using jinja2 templates
• Run commands before starting service

Usages

Install in container

All you need to do is to setup a yaml file called entrypoint-config.yml and to install pyentrypoint in your Dockerfile using pip.

FROM        debian
# Installing git for example
RUN         apt-get update && apt-get install git python-pip -y
# Install pyentrypoint
RUN         pip install pyentrypoint
# Copy config file in the current WORKDIR
COPY        entrypoint-config.yml .
# Set ENTRYPOINT
ENTRYPOINT  ['pyentrypoint']
# git will be the default command
CMD         ['git']

Setup entrypoint

This is an example of entrypoint-config.yml file.

# Entrypoint configuration example

# This entry should reflect CMD in Dockerfile
command: git

# This is a list with some subcommands to handle
# when CMD is not `git` here.
# By default, all args started with hyphen are handled.
subcommands:
    - "-*"
    - clone
    - init
    - ls-files
    # etc...

# User and group to run the cmd.
# Can be name or uid/gid.
# Affect only command handled.
# Dockerfile USER value by default.
user: 1000
group: 1000

# These files should exist (ADD or COPY)
# and should be jinja templated.
config_files:
    - /etc/gitconfig
    - .ssh/config
    - .ssh/id_rsa

# These environment variables will be wiped before
# exec command to keep them secret
# CAUTION: if the container is linked to another one,
# theses variables will passed to it anyway
secret_env:
    - SSHKEY

# Links are handled here
# Port, name, protocol or env variable can be used to identify the links
# Raise an error if the link could not be identified
links:
    'ssh':
        port: 22
        name: 'ssh*'
        protocol: tcp
        # env can be list, dictionary or string
        env:
            FOO: bar
        # Single doesn't allow multiple links for this ID
        # false by default
        single: true
        # Set to false to get optional link
        # true by default
        required: true

# Commands to run before applying configuration
pre_conf_commands:
    - echo something > to_this_file

# commands to run after applying configuration
post_conf_commands:
    - echo "something else" > to_this_another_file

# Cleanup environment from variables created by linked containers
# before running command (True by default)
clean_env: True

# Enable debug to debug
debug: true

Config templates

You can generate configuration for your service with jinga2 template.

Here an example for an hypothetical ssh config file:

host server:
    hostname {{links.ssh.ip}}
    port {{links.ssh.port}}

Templates with be replaced with ip address and port of the identified link. All links can be accessed from links.all, this is a tuple of links you can iterate on it.

{% for link in links.all %}
host {{link.names[0]}}
    hostname {{link.ip}}
    port {{links.port}}
{% endfor %}

If you change the option single to false in the entrypoint-config.yml, the identified link ssh will become a tuple of links. You must iterate on it in the jinja template.

{% for link in links.ssh %}
host {{link.names[0]}}
    hostname {{link.ip}}
    port {{links.port}}
{% endfor %}

Accessible object

You have 4 available objects in your templates.

• config
• links
• containers
• environ

config

Config reflect the config file. You can retrieve any setup in this object.

(see config.py)

links

Links handles Link objects. You can identify links using globing patterns in the configuration file.

link is related to one physical link (one ip and one port).

link handles the following attributes:

• ip
  • link ip
• port
  • link port (integer)
• environ
  • related container environment
• protocol
  • link protocol (tcp or udp)
• uri
  • link uri (example: tcp://10.0.0.3:80)
• names
  • tuple of related container names

containers

containers handles a tuple of container object.

container handles the following attributes:

• ip
  • container ip
• environ
  • container environment
• names
  • List of containers names
    • Names are sorted by length, but container ID will be the last element.
• id
  • Hexadecimal container ID (if available, else empty string)
• links
  • Tuple of link object related to this container

environ

environ is the environment of the container (os.environ).

Setup

Some setups can be overridden using environment variables.

ENTRYPOINT-CONFIG overrides entrypoint-config.yml file.

Running Tests

To run tests, ensure that docker-compose and make are installed and run

$ make test