I have made a web real time application that connected to Node.js server through a websocket. In my website I can turn on/off an LED connected to Arduino Uno.
What I want to do is, I want my website have capability to turn on/off led at certain date and time dynamically. What I mean 'dynamically' is I can add new or remove current schedule task.
I have been trying using node-schedule, cron, but it's just a static schedule task. I can't change or add new task.
Use a db / file. You can store the dates in a json and then edit it as per your convenience. Use node-cron to create events of what you wanna do from the data. Create function that removes entry from json when you want to and it also remove it from the upcoming tasks by task.destroy() method of node-cron.
https://github.com/kdichev/Green-Systems/blob/development/PumpController.js
check what I have done with my pump. on line 19 I have an array of times that will run the pump according to the entries given.
Related
I have a node.js express app with MongoDB database and what I want is to be able to update the database based on time
Interval. For example
Increase a number field automatically every 7 days for each user based on an activation date set on each document.
Please how do I achieve this?
You can use cron jobs for that.
A cron job used for scheduling tasks to be executed sometime in the future at specific time interval.
Find out more here:
You will schedule a cron job that will run once in a day and you will add your code to be executed.
The What are Database Triggers? documentation indicates triggers, however it's not clear if that available on the free Community Edition, or only on their hosted Atlas offering. If you can't figure out a Mongo trigger solution, you would have to code a controller in Node.js based on .setInterval to fetch user creation date(s) then insert whatever update(s) you want on the user(s).
Types of Database Triggers MongoDB provides three types of triggers:
Database Triggers: Perform some type of action when a document is updated, added, or removed.
Scheduled Triggers: Scheduled actions that occur at a specific time or set interval. MongoDB Atlas leverages an intuitive approach to
scheduling triggers using the CRON expression language. These types of
triggers can be as simple as running a daily clean-up process of
temporary records, to generate a minute-by-minute report on
transaction anomalies.
Authentication Triggers (Realm only): Actions that happen when creating or deleting a user or on login into MongoDB. These types of
triggers are for performing user maintenance or user audit tracking
for Realm apps.
I am creating an IOT device where the user can set a particular time to trigger an action by an IOT device. For eg: At 01:00 PM, the Air Conditioner starts automatically. In this case, user will set 01:00PM in the Mobile App which will further be stored the value in a database table.
Now i need to read these database values and trigger an Azure function that will switch on the A/C, but this process is complex since i need to write my own scheduler.
Is there any alternate way, perhaps using Azure Timer Functions.
Thanks
I am serving my users with data fetched from an external API. Now, I don't know when this API will have new data, how would be the best approach to do that using Node, for example?
I have tried setInterval's and node-schedule to do that and got it working, but isn't it expensive for the CPU? For example, over a day I would hit this endpoint to check for new data every minute, but it could have new data every five minutes or more.
The thing is, this external API isn't ran by me. Would the only way to check for updates hitting it every minute? Is there any module that can do that in Node or any approach that fits better?
Use case 1 : Call a weather API for every city of the country and just save data to my db when it is going to rain in a given city.
Use case 2 : Send notification to the user when a given Philips Hue lamp is turned on at the time it is turned on without having to hit the endpoint to check if it is on or not.
I appreciate the time to discuss this.
If this external API has no means of notifying you when there's new data, then the only thing you can do is to "poll" it to check for new data.
You will have to decide what an "efficient design" for polling is in your specific application and given the type of data and the needs of the client (what is an acceptable latency for new data).
You also need to be sure that your service is not violating any terms of service with your polling scheme or running afoul of rate limiting that may deny you access to the server if you use it "too much".
Would the only way to check for updates hitting it every minute?
Unless the API offers some notification feature, there is no other scheme other than polling at some interval. Polling every minute is fairly quick. Do your clients really need information that is less than a minute old? Or would it really make no difference if the information was as much as 5 minutes old.
For example, in your example of weather, a client wouldn't really need temperature updates more often than probably every 10-15 minutes.
Is there any module that can do that in Node or any approach that fits better?
No. Not really. You'll probably just use some sort of timer (either repeated setTimeout() or setInterval() in a node.js app to repeatedly carry out your API operations.
Use case: Call a weather API for every city of the country and just save data to my db when it is going to rain in a given city.
Trying to pre-save every possible piece of data from an external API is probably a losing proposition. You're essentially trying to "scrape" all the data from the external API. That is likely against the terms of service and will likely also run afoul of rate limits. And, it's just not very practical.
Instead, you will probably want to fetch data upon demand (when a client requests data for Phoenix, then, and only then, do you start collecting data for Phoenix) and then once a demand for a certain type of data (temperatures in a particular city) is established, then you might want to pre-cache that data more regularly so you can notify clients of changes. If, after awhile, no clients are asking for data from Phoenix, you stop requesting updates for Phoenix any more until a client establishes demand again.
I have tried setInterval's and node-schedule to do that and got it working, but isn't it expensive for the CPU? For example, over a day I would hit this endpoint to check for new data every minute, but it could have new data every five minutes or more.
Making a remote network request is not a CPU intensive operation, even if you're doing it every minute. node.js uses non-blocking networking so most of the time during a network request, node.js isn't doing anything and isn't using the CPU at all. The only time the CPU would be briefly used is when you first send the API request and then when you receive back the result from the API call and need to process it.
Whether you really need to "poll" every minute depends upon the data and the needs of the client. I'd ask yourself if your app will work just fine if you check for new data every 5 minutes.
The method I would use to update would be contained outside of the code in a scheduled batch/powershell/bash file. In windows you can schedule tasks based upon time of day or duration since last run, so what you could do is run a simple command that will kill your application for five minutes, run npm update, and then restart your application before closing the shell.
That way you're staying out of your API and keeping code to a minimum, and if your code is inside that Node package in the update, it'll be there and ready once you make serious application changes or you need to take the server down for maintenance and updates to the low-level code.
This is a light-weight solution for you and it's a method I've used once or twice at my workplace. There are lots of options out there, and if this isn't what you're looking for I can keep looking out for you.
I'm building a website that some users will enter and after a specific amount of time an algorithm has to run in order to take the input of the users that is stored in the database and create some results for them storing the results also in the database. The problem is that in nodejs i cant figure out where and how should i implement this algorithm in order to run after a specific amount of time and only once(every few minutes or seconds).
The app is builded in nodejs-expressjs.
For example lets say that i start the application and after 3 minutes the algorithm should run and take some data from the database and after the algorithm has created some output stores it in database again.
What are the typical solutions for that (at least one is enough). thank you!
Let say you have a user request that saves url to crawl and get listed products
So one of the simplest ways would be to:
On user requests create in DB "tasks" table
userId | urlToCrawl | dateAdded | isProcessing | ....
Then in node main site you have some setInterval(findAndProcessNewTasks, 60000)
so it will get all tasks that are not currently in work (where isProcessing is false)
every 1 min or whatever interval you need
findAndProcessNewTasks
will query db and run your algorithm for every record that is not processed yet
also it will set isProcessing to true
eventually once algorithm is finished it will remove the record from tasks (or mark some another field like "finished" as true)
Depending on load and number of tasks it may make sense to process your algorithm in another node app
Typically you would have a message bus (Kafka, rabbitmq etc.) with main app just sending events and worker node.js apps doing actual job and inserting products into db
this would make main app lightweight and allow scaling worker apps
From your question it's not clear whether you want to run the algorithm on the web server (perhaps processing input from multiple users) or on the client (processing the input from a particular user).
If the former, then use setTimeout(), or something similar, in your main javascript file that creates the web server listener. Your server can then be handling inputs from users (via the app listener) and in parallel running algorithms that look at the database.
If the latter, then use setTimeout(), or something similar, in the javascript code that is being loaded into the user's browser.
You may actually need some combination of the above: code running on the server to periodically do some processing on a central database, and code running in each user's browser to periodically refresh the user's display with new data pulled down from the server.
You might also want to implement a websocket and json rpc interface between the client and the server. Then, rather than having the client "poll" the server for the results of your algorithm, you can have the client listen for events arriving on the websocket.
Hope that helps!
If I understand you correctly - I would just send the data to the client-side while rendering the page and store it into some hidden tag (like input type="hidden"). Then I would run a script on the server-side with setTimeout to display the data to the client.
Im building an API with node and express running with a mongoDB for a mobile application, and basically it needs to trigger an event after a time period. For example:
A Request will come in for a driver who is needed in 30 minutes, I need the API to hang onto that record and after 25 minutes, query for the nearest driver and send them a notification with the details.
Does anyone know how to handle something like that on the server side?
You need to implement some sort of background job. There are a few packages out there which do exactly what you want.
Essentially they push some metadata about the task you need to complete independently off your app, in the future, and when that time comes the data is used to process the task at hand.
Here are are a couple packages:
Kue
Bee Queue
There's even a short tutorial that someone wrote which uses Kue.