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PXP Agent

This is the agent for the PCP Execution Protocol (PXP), based on the the Puppet Communications Protocol (PCP). It enables the execution of actions on remote nodes, via PXP. The pxp-agent needs to be connected to a PCP broker in order to be used; please refer to the documentation below for how to do that.

Building from source

Build requirements

  • a C++11 compiler (clang/gcc 4.7)
  • gnumake
  • cmake
  • boost
  • ruby (2.0 and newer)

Build with make and make install

Starting the agent

pxp-agent should be configured in your system to be executed automatically as a service. In case you need to run it manually, you can invoke directly its executable file; after building from source, it is located in the ./build/bin directory; in case an installer was used, the default locations are:

  • *nix: /opt/puppetlabs/puppet/bin/pxp-agent
  • Windows: C:\Program Files\Puppet Labs\Puppet\pxp-agent\bin\pxp-agent.exe

Configuration options can be passed as command line arguments or by using a configuration file (see below).

The agent will execute as a background process by default; in that case, it prevents multiple instances running at the same time. Please refer to the following sections for platform-specific behavior.

*nix

In case --foreground is unflagged, pxp-agent will start as a daemon and its PID will be stored in /var/run/puppetlabs/pxp-agent.pid, or in another location if specified by --pidfile. pxp-agent will rely on such file to prevent multiple daemon instances from executing at once. The PID file will be removed if the daemon is stopped by using one of SIGINT, SIGTERM, or SIGQUIT signals.

Windows

pxp-agent relies on nssm to execute as a service. In case --foreground is unflagged, a mutex-based mechanism will prevent multiple instances of pxp-agent. Note that no PID file will be created.

Starting unconfigured

If no broker WebSocket URI, SSL key, ca or cert value is supplied, the agent will still be able to start in unconfigured mode. In this mode no connection will be established but the process will not terminate.

Exit code

On success, pxp-agent returns 0. In case of it fails to parse the command line options or the configuration file, it returns 2. For all other failures, including invalid options, it returns 1.

Modules

Actions are grouped in modules, by which they can be loaded and configured within pxp-agent. An example of module is given by the Puppet module.

Modules interface

A module is a file that provides the module metadata and an interface to execute its actions.

The module metadata is a JSON object containing the following entries:

  • configuration: an object that specifies options that may be included in a separate configuration file (see below);
  • actions: a JSON array containing specifications for the input and output of each action.

For a trivial example of module, please refer to the reverse module used for testing.

pxp-agent will execute a module to retrieve its metadata (by passing no argument) and to run a given action (by invoking the action with the input specified in the PXP request). Normally when pxp-agent calls a module it must be executable. When the interpreter field is specified in the configuration file (see below), pxp-agent will use this value to execute the module instead.

Note that the transaction status module is implemented natively; there is no external file for it. Also, status query requests must be blocking.

Modules configuration

Modules can be configured by placing a configuration file in the --modules-config-dir. Config options must be specified in the module metadata (see above). Module config files are named like module_name.conf.

Configuring the agent

The PXP agent is configured with a config file. The values in the config file can be overridden by supplying arguments on the command line.

The agent will look for the default config file in:

  • *nix: /etc/puppetlabs/pxp-agent/pxp-agent.conf
  • Windows: C:\ProgramData\PuppetLabs\pxp-agent\etc\pxp-agent.conf

A different config file can be specified by passing the --config-file option.

The config files use the JSON format. Options must be specified as entries of a single JSON object. Example:

{
    "broker-ws-uri" : "wss://127.0.0.1:8142/pcp/",
    "ssl-key" : "/etc/puppetlabs/puppet/ssl/private_keys/myhost.net.pem",
    "ssl-ca-cert" : "/etc/puppetlabs/puppet/ssl/certs/ca.pem",
    "ssl-cert" : "/etc/puppetlabs/puppet/ssl/certs/myhost.net.pem"
}

Note that you have to specify the WebSocket secure URL of the PCP broker in order to establish the WebSocket connection on top of which the PCP communication will take place.

Logging

By default, log messages will be written to:

  • *nix: /var/log/puppetlabs/pxp-agent/pxp-agent.log
  • Windows: C:\ProgramData\PuppetLabs\pxp-agent\var\log\pxp-agent.log.

You can specify a different file with the --logfile option.

When running in foreground mode, it is possible to display log messages on console by using an hyphen instead of a file path: --logfile -.

The default log level is info. You can specify a different log level by using the --loglevel option with one of the following strings: none, trace, debug, info, warning, error, fatal.

List of all configuration options

The PXP agent has the following configuration options

config-file (optional)

Specify which config file to use.

broker-ws-uri (required to connect)

The WebSocket URI of the PXP broker you wish to connect the agent to, example wss://192.168.0.1:8142/pxp/

ssl-ca-cert (required to connect)

The location of your SSL Certificate Authority certificate, example /etc/puppet/ssl/ca/ca_crt.pem

ssl-cert (required to connect)

The location of the pxp-agent SSL certificate, example /etc/puppet/ssl/certs/bob_crt.pem

ssl-key (required to connect)

The location of the pxp-agent's SSL private key, example /etc/puppet/ssl/certs/bob_key.pem

logfile (optional)

The path of the log file.

loglevel (optional)

Specify one of the following logging levels: none, trace, debug, info, warning, error, or fatal; the default one is info

modules-dir (optional)

Specify the directory where modules are stored

modules-config-dir (optional)

Specify the directory containing the configuration files of modules

spool-dir (optional)

The location where the outcome of non-blocking requests will be stored; the default location is:

  • *nix: /opt/puppetlabs/pxp-agent/spool
  • Windows: C:\ProgramData\PuppetLabs\pxp-agent\var\spool

foreground (optional flag)

Don't become a daemon and execute on foreground on the associated terminal.

*pidfile (optional; only on nix platforms)

The path of the PID file; the default is /var/run/puppetlabs/pxp-agent.pid