Let's say, I have an application that is written in NodeJs, that process the latest blocks of the steem blockchain and write data into a database. I have three ways of running it on my server.
As you probably know, when you are disconnected from a SSH session, the programs that are launched in the session will be terminated. There is any easy way to fix this. You can start a session by using command
screen -S name before you run any long-running program e.g. system updates or a program that needs to run forever.
In case the SSH is disconnected, the programs will be still running. And you can use command
screen -r name to re-connect to the session. You can
screen -ls to list the current sessions, and
screen -d name to detach a session.
The advantage of using this method is:
- you can easily monitor the application (by seeing its output)
- you can easily terminate or restart the application e.g. Ctrl + C
- the application runs continuously, meaning that you can keep up to the latest blocks and provide a less than 3 second sync time.
- If the application exists abnormaly, it is not restarted automatically - thus you would need to add the error-handling in your code.
- Long-running code may tend to have more problems: e.g. memory-leaks, crash at some point.
Putting it in Crontab
Another way is to run your program in crontab. However, the finest granularity is every minute i.e. you can specify your application to run every minute.
- You probably don't need to do error-handling. In case it fails, it fails. You can just wait for next minute (restart automatically).
- Not to worry about memory leaks. It is less likely to go wrong due to memory issue.
- Lose the ability to sync real-time with the blocks
- Not easy to monitor the output (you can redirect the errors to files though)
Using a Process Manager
You can combine the both advantages using a Process Manager. For example, if it is a NodeJs application, you can use
- automatically restart your application in case it crashes or some conditions are met e.g. memory constraints, age.
- easy to monitor the output of each application e.g. you can
pm2 show app
- easy to terminate
pm2 delete appor restart
pm2 restart app
- the application runs continuously
- error-handling is optional - but considered a good practise not to let
pm2restart your app.
Every little helps! I hope this helps!
Reposted to Blog
Also: you can vote me at the tool I made: https://steemyy.com/witness-voting/?witness=justyy