{"id":1098,"date":"2018-04-05T13:00:03","date_gmt":"2018-04-05T12:00:03","guid":{"rendered":"http:\/\/chewett.co.uk\/blog\/?p=1098"},"modified":"2020-09-26T22:09:18","modified_gmt":"2020-09-26T21:09:18","slug":"raspberry-pi-cluster-node-06-sending-slave-details-to-the-master","status":"publish","type":"post","link":"https:\/\/chewett.co.uk\/blog\/1098\/raspberry-pi-cluster-node-06-sending-slave-details-to-the-master\/","title":{"rendered":"Raspberry Pi Cluster Node \u2013 06 Sending Slave Details to the Master"},"content":{"rendered":"\n

This post builds on my previous posts in the Raspberry Pi Cluster series<\/a> by changing how the slave sends messages. From now on the slave will send useful information about the system to the master. The master will also be configured to receive messages of many types.<\/p>\n\n\n\n\n\n\n\n

Changing the message format<\/h2>\n\n\n\n

To start with I have coded it so that sending JSON messages between the nodes would print out the message. Now I am going to change it so that it can send different types of messages.<\/p>\n\n\n\n

To do this I am first going to change the format I use to send messages. To do this I am going to modify create_msg_payload<\/code> function to be more useful.<\/p>\n\n\n\n

def create_payload(payload, payload_type=\"message\"):\n    return json.dumps({\"type\": payload_type, \"payload\": payload}) + MESSAGE_SEPARATOR<\/pre><\/pre>\n\n\n\n
Here I have renamed the function and added a new parameter to the function, payload_type<\/code>. This is currently set to default to the string message<\/code>.<\/p>\n\n\n\n
The format I am using to send data has been changed to a more generic one with two keys, type<\/code> and payload<\/code>. This allows me to send a simple string or a more complex object if required. The master will handle each payload differently based on the string in the type field.<\/p>\n\n\n\n
Now I have a flexible system able to send any data and payload I require. I will talk about how the master can then handle each different type later.<\/p>\n\n\n\n
Getting useful system information<\/h2>\n\n\n\n
To make the slave a little more interesting I am going to add a new type of payload, the machine_details<\/code> payload. This is going to include a number of details about the slave to pass to the master.<\/p>\n\n\n\n
In the future I am going to use this information to judge what slaves should perform what tasks. This is important as certain tasks may require specific machine requirements, such as a minimum amount of system RAM.<\/p>\n\n\n\n
I am going to send the hostname, CPU percentage used, RAM, CPU type, and the number of CPU cores. To get this data I am going to use a number of different python libraries in the slave script. Below I import the required python libraries to send the data I want to the master.<\/p>\n\n\n\n
import socket\nimport psutil\nimport platform\nimport multiprocessing<\/pre><\/pre>\n\n\n\n
Now I have these libraries I can create my object to send to the master.<\/p>\n\n\n\n
machine_details = {\n    'hostname': socket.gethostname(),\n    'cpu_percent_used': psutil.cpu_percent(1),\n    'ram': psutil.virtual_memory().total,\n    'cpu': platform.processor(),\n    'cpu_cores': multiprocessing.cpu_count()\n}<\/pre><\/pre>\n\n\n\n
Above I have created the machine_details object that I will send across. I will detail what I am using for each section and what it returns below.<\/p>\n\n\n\n