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NethServer 8

Module agent

Base actions

Agent task processing is defined by actions. An action is a directory containing one ore more executable scripts called steps. See the agent README for the complete story.

The core provides a set of base actions defined in /usr/local/agent/actions and inherited by module agents.

  • create-module: executed upon installation, it automatically downloads the module image and all images listed inside org.nethserver.images label.
  • destroy-module: executed on module removal; modules can add here scripts to clean up configuration, like Traefik routes, Firewalld, system-wide Systemd units…
  • get-status: used by the UI, it returns the current module status, like the node where the application is running, used images and volumes, systemd units status. This action works correctly only for rootless modules.
  • list-service-providers: Look up provider information for a given service name and other filtering criteria. See also Service providers

Every agent has also a builtin list-actions action. This command lists the actions provided by the agent of module/traefik1:

api-cli run --agent module/traefik1 list-actions | jq

As a convention, all modules with a UI should also implement the following actions:

  • configure-module: it validates the user input and applies the configuration, see Dokuwiki example
  • get-configuration: it should return current configuration, the output should be equal or similar to configure-module input, see Dokuwiki example

Agent environment

Environment variables are copied to Redis at module/<module_id>/environment.

Each action has access to environment variables. They are:

  1. initialized by add-module
  2. changed by the agent at run time
  3. inherited from the agent environment

Main environment variables are:

  • MODULE_ID: the ID of the instance, i.e. myapp1
  • NODE_ID: the node ID where the action is running, i.e. 1
  • <name>_IMAGE: see Image download
  • TCP_PORT, TCP_PORTS, TCP_PORTS_RANGE: see Port allocation

Other available variables:

  • AGENT_COMFD: the file descriptor to talk to the agent via action commands
  • AGENT_TASK_ID: the unique ID of current task, i.e. c0b8b976-9444-42d5-a40b-142a6a483a84
  • AGENT_TASK_ACTION: the name of executed action, i.e.: create-module
  • AGENT_INSTALL_DIR
  • AGENT_STATE_DIR
  • AGENT_ID
  • IMAGE_ID
  • IMAGE_URL
  • IMAGE_DIGEST
  • IMAGE_REPODIGEST

Environment variables added by the add-module and defined at run time are saved inside /home/<module_id>/.config/state/environment, e.g. /home/myapp1/.config/state/environment.

To run a command within an agent environment, use the runagent wrapper. For instance this command prints the agent environment of the rootfull module promtail1.

runagent -m promtail1 env

Agent commands

During the action execution, action steps can talk to the agent using a simple protocol. It is possible to set/unset environment variables, dump the environment to a well known file, etc.

See all available action commands.

The protocol is implemented by the Python agent package.

Python example:

import agent

agent.set_env('MYVAR', 'value')
agent.dump_env()

Validation

See validation framework.