Monitoring & control

Control

DARC is controlled by a master service, DARCMaster. This service controls all other services and takes care of starting/stopping observations. It also holds the Python queues that connect different services together. The darc_service starts the master service. However, the user is advised to use one of the supplied scripts to start DARC (see scripts).

The master service listens for commands on a network port. DARC includes an executable to handle communication with the master service (see command line interface), but this can also be done from Python. For example:

>>> from darc.control import send_command
>>> output = send_command(timeout=5, service='processor', host='arts001', command='status')
status: Success
message: {'processor': 'running'}
>>> output
{'status': 'Success', 'message': {'processor': 'running'}}

send_command returns a dictionary, unless something failed in which case it returns None.

Command line interface

The user can interact with DARCMaster through the darc executable. All options can be listed by running darc -h. A few examples:

arts@arts041:~$ darc --service all status
status: Success
message: {'offline_processing': 'running', 'status_website': 'running', 'voevent_generator': 'running', 'lofar_trigger': 'running', 'processor': 'running'}

arts@arts041:~$ darc --service lofar_trigger get_attr log_file
status: Success
message: {'lofar_trigger': "{'LOFARTrigger.log_file': /home/arts/darc/log/lofar_trigger.arts041.log}"}

arts@arts041:~$ darc lofar_status
status: Success
message: LOFAR triggering is enabled

arts@arts041:~$ darc --host arts001 --service amber_clustering restart
status: Success
message: {'amber_clustering': {'stop': 'stopped', 'start': 'started'}}

arts@arts041:~$ darc --host nonexistent --service all status
Failed to connect to DARC master: [Errno -2] Name or service not known

arts@arts041:~$ darc stop_master
status: Success
message: Stopping master

Note

The start_observation and stop_observation commands are normally executed by ARTSSurveyControl and should not be executed by the user.

Scripts

DARC comes with several scripts to make control of the pipeline easier:

• darc_start_master: Starts the master service on the current node and checks whether it starts up properly. It also redirects the output to a log file located at $HOME/darc/log/darc_master.<hostname>.log.

• darc_stop_master: Stops the master service an by extension all other services, also aborting any running observations.

• darc_start_all_services: Starts all services, including DARC Master if it is not running.

• darc_start_stop_all_services: Stops all services except the master service. Aborts any running observation.

• darc_kill_all: Kill master service and all other services. Use when DARC fails to exit using the normal stop command.

In addition, the following two commands are available on the ARTS cluster:

• start_full_pipeline: Starts all DARC services on all nodes

• stop_full_pipeline: Stops DARC services, including master service, on all nodes.

Monitoring

Status website

This is handled by the StatusWebsite service, which runs on the master node. It generates a simple web page showning whether or not the DARC services are online on each node of the ARTS cluster. If a node cannot be reached, it turns grey. Otherwise each service on the node is checked and shown in green if it is running, and in red if it is not.

Logging

Each service has its own log file, by default located at $HOME/darc/log/<service>.<hostname>.log. The log files include timestamps, allowing the user to check what happened at some point in the past.