pyentrypoint

pyentrypoint is a tool written in Python to manage 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
• Reload service when configuration has changed

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']

FROM        alpine
# Installing git for example
RUN         apk add --update py-pip git
# 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']

Using docker-image

FROM    goldy/pyentrypoint:python3

# ONBUILD statement add entrypoint-config.yml in current directories

Available with many flavours:

• goldy/pyentrypoint:python2
• goldy/pyentrypoint:python3
• goldy/pyentrypoint:python2-alpine
• goldy/pyentrypoint:python3-alpine

Working examples

• Tor hidden service

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.
# Note: if config files end with ".tpl", the extension will be removed.
config_files:
    - /etc/gitconfig
    - .ssh/config.tpl # Will apply to ".ssh/config"
    - /tmp/id_rsa: .ssh/id_rsa # Will apply "/tmp/id_rsa" template to ".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
    - '*' # Support globbing, all environment will be wiped

# 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
# This is not supported when using docker network or docker-compose v2.
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

post_run_commands:
    - echo run commands after started service

# Reload service when configuration change by sending a signal to process
reload:
    signal: SIGHUP # Optional, signal to send, default is SIGHUP
    pid: 1 # Optional, pid to send signal, default is 1
    watch_config_files: true # Optional, watch defined config files, default True
    files: # Optional, list of files to watch
        - /etc/conf/to/watch
        - /file/support/*.matching
# can also be enabled like this:
reload: true


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

# Enable debug to debug
debug: true

# Do not output anything except error
quiet: false

Config templates

You can generate configuration for your service with jinja2 template.

links and containers are not supported with docker network and docker-compose v2.

Here is an example for an hypothetical ssh config file:

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

Templates will 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 %}

Accessing environment in template.

{% if 'SSHKEY in env' %}
{{env['SSHKEY']}}
{% endfor %}

Accessible objects

You have 4 available objects in your templates.

• config
• links
• containers
• environ
• yaml
• json

config

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

(see config.py)

links

Not supported with docker network and docker-compose v2

Links handles Link objects. You can identify links using wildcard 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

Not supported with docker network and docker-compose v2

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, empty string else)
• links
  • Tuple of link objects related to this container

environ

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

env is an alias to environ.

yaml and json

yaml and json objects are respectively an import of PyYAML and json modules.

They are useful to load and dump serialized data from environment.

# Here yaml is present in SETUP_YAML environment variable
{% set data = yaml.load(env['SETUP_YAML'])%}
{{data['param']}}

# Here json is present in SETUP_JSON environment variable
{% set data = json.loads(env['SETUP_JSON'])%}
{{data['param']}}

Setup

Some setups can be overridden using environment variables.

• ENTRYPOINT_CONFIG overrides path of entrypoint-config.yml file.
• ENTRYPOINT_FORCE is applying configuration and runs pre and post conf commands even if the command provided is not handled.
• ENTRYPOINT_PRECONF_COMMAND run an extra pre conf shell command after all pre conf commands.
• ENTRYPOINT_POSTCONF_COMMAND run an extra post conf shell command after all post conf commands.
• ENTRYPOINT_DEBUG enables debug logs.
• ENTRYPOINT_RAW does not use logging to display pre and post conf commands. This can be useful if output is serialized.
• ENTRYPOINT_DISABLE_RELOAD disable reload system even if it is enabled in entrypoint-config.yml.
• ENTRYPOINT_USER overrides user in config.
• ENTRYPOINT_GROUP overrides group in config.
• ENTRYPOINT_DISABLE_SERVICE exits container with 0 before doing anything. Useful to disable container using environement.

Running Tests

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

$ make test