aws_mqtt_client - bruno-beloff/scs_dev GitHub Wiki
docs > software repositories > scs_dev > commands > subscribing to / publishing live data
DESCRIPTION
The aws_mqtt_client utility is used to subscribe or publish using the South Coast Science / AWS messaging infrastructure.
Documents for publication are gained from stdin by default, otherwise from the specified Unix domain socket (UDS). Likewise, documents gained from subscription are written to stdout, or a specified UDS.
Subscriptions can be specified either by a project channel name, or by an explicit messaging topic path. Documents gained by subscription may be delivered either to stdout, or to a specified Unix domain socket.
In order to operate effectively in environments with unreliable communications, the aws_mqtt_client buffers messages prior to publication. The size of the buffer is set by the scs_mfr/mqtt_conf utility.
An explanation of the LED colour patters generated by the aws_mqtt_client utility are detailed in the Wiki entry Praxis LED colours.
The aws_mqtt_client utility requires AWS client authorisation to operate.
Only one MQTT client should run at any one time, per TCP/IP host.
SYNOPSIS
aws_mqtt_client.py [-p UDS_PUB] [-s] { -c { C | G | P | S | X } (UDS_SUB_1) | [SUB_TOPIC_1 (UDS_SUB_1) .. SUB_TOPIC_N (UDS_SUB_N)] } [-e] [-l LED_UDS] [-v]
| Options | |
|---|---|
| --version | show program's version number and exit |
| -h, --help | show this help message and exit |
| -p UDS_PUB_ADDR, --pub-addr=UDS_PUB_ADDR | read publications from UDS instead of stdin |
| -s, --sub | write subscriptions to UDS instead of stdout |
| -c CHANNEL, --channel=CHANNEL | subscribe to channel |
| -e, --echo | echo input to stdout (if not writing subscriptions to stdout) |
| -l LED_UDS, --led=LED_UDS | send LED commands to LED_UDS |
| -v, --verbose | report narrative to stderr |
EXAMPLES
( cat < /home/scs/SCS/pipes/mqtt_publication_pipe & ) | /home/scs/SCS/scs_dev/src/scs_dev/aws_mqtt_client.py -v -cX -l /home/scs/SCS/pipes/scs_led_control.uds > /home/scs/SCS/pipes/control_subscription_pipe
FILES
~/SCS/aws/aws_client_auth.json
~/SCS/aws/certs/NNNNNNNNNN-certificate.pem.crt
~/SCS/aws/certs/NNNNNNNNNN-private.pem.key
~/SCS/aws/certs/NNNNNNNNNN-public.pem.key
~/SCS/aws/certs/root-CA.crt
SEE ALSO
scs_dev/aws_topic_publisher
scs_dev/aws_topic_subscriber
scs_dev/led_controller
scs_mfr/aws_client_auth
scs_mfr/aws_project
scs_mfr/mqtt_conf
BUGS
When run as a background process, aws_mqtt_client will exit if it has no stdin stream.