add cron and ping members to get last seen time

[NoobTW]

Pull Request type

Please check the type of change your PR introduces:

• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no API changes)
• Build-related changes
• Documentation content changes
• Other (please describe):

What is the current behavior?

Issue Number: #40

What is the new behavior?

• Add pingAll function in utils/ping.js to ping every members in a network, and update in database.
• Add node-cron package and ping all networks every 5 minutes.

Does this introduce a breaking change?

• Yes
• No

Other information

There's no changes at the frontend side yet.

[lgtm-com]

This pull request introduces 2 alerts when merging d3fdac6 into 54ec767 - view on LGTM.com

new alerts:

• 1 for Useless assignment to local variable
• 1 for Variable not declared before use

[dec0dOS]

Hello, @NoobTW!

Thanks a lot for your work. That is a great start to fully implement the last seen time feature. Initially, I thought that this feature would require much more effort.

There are some things to mention. In your PR you're deleting the yarn.lock file. Is this was a mistake or you're having some troubles in installing the dependencies?
Will you help with the frontend side or should I merge it in the current state in the dev branch?

[NoobTW]

In your PR you're deleting the yarn.lock file.

Yes, I believe this is a mistake from me because I use npm instead of yarn. Feel free to add it back, or maybe i can commit it later.

Will you help with the frontend side or should I merge it in the current state in the dev branch?

Before merging this PR, i want to check if ping members every 5 minutes is OK? if it's ok then I think you can merge it for now.

As for the frontend side, I would like to help with the frontend side but i don't know how to do it for now. (e.g., Can we get the lastSeen property from the current backend API? I haven't check for that yet.)

Last but not least, thank you for your great work for building this self-host controller and the great UI.

[dec0dOS]

Before merging this PR, i want to check if ping members every 5 minutes is OK? if it's ok then I think you can merge it for now.

I think that this value should be configurable. Anyway, 1 minute is a better default value for troubleshooting. Also, there should be a way to disable the 'last seen time' option.