Prefect

Lightweight manager for running processes.

Install

Run below command to download and install the prefect tool.

curl -fsSL https://github.com/aravinda/prefect/releases/latest/download/install.sh | sudo bash -x

Usage

Start the Service manager service.

prefect mgr --svc-dir=/home/ubuntu/services

Add a new service

prefect add <name> <arg1> <arg2> ...

export PREFECT_DIR=/home/ubuntu/services
prefect add kadalu-mgr "/usr/sbin/kadalu mgr --port=3000" --auto-restart

Above command creates a service file under SVC_DIR ($PREFECT_DIR/kadalu-mgr.json). Also caches the content in memory.

Delete a service

prefect delete kadalu-mgr

This deletes the service file.

List the managed services

prefect status

Send signal to a service

prefect signal <service-name> <signal>
prefect signal kadalu-mgr SIGHUP

Restart the service

prefect restart <service-name>

Terminates the running service by looking at PID and then service manager will take care of starting it.

Update the args or change the service

prefect update kadalu-mgr /usr/local/sbin/kadalu mgr --port=3001

This command updates the service file.

How it works?

Service manager gets the list of service files exists in the SVC_DIR and starts all the services. It periodically watches the service files to identify the new services, modified services and deleted services. Send SIGHUP to trigger the reload of service files if the interval is not suitable.

• If in-memory service data is not available but service file exists, NEW service
• If in-memory service data is different from the service file content, MODIFIED service
• If in-memory service data is not available as file, DELETED service

On fresh start, all the services are identified as NEW