I want to replace my cron job with apache kafka using php.
Is this possible?
Now my cron does work as updation on databases. Also sending email, sms depend on conditions. Also periodically updation in databases.
And daily backup of database.
Is it possible to implement this using kafka
You need to design your entire environment in terms of events rather than "batch time slots", but yes, it's possible in theory. As a shim, you can start with a Kafka process in Cron that will read messages for a configurable amount of time (or max amount of messages), and then process that chunk.
As for what you have asked for, you can make a CDC / changelog topic for database events (if you make this a compacted topic, you remove the need for a daily backup, as every database event is persistent in Kafka from the beginning of your DB history - look at the Debezium project for a starting point), and you can derive corresponding emails or sms topics which you have consumers polling and firing off SMTP, SMS, or GCM/APNs messages as you're probably already doing if this is the system you are migrating from.
None of this necessarily needs to be in PHP either (or really Kafka over another pub-sub system, for that matter). I would implore you to consider a microservices based approach that uses a client library and technology that makes most sense for your use cases. For example, AWS can integrate Kinesis (or MSK)+SNS+SES and you have an equivalent Kafka+SMS+Email solution with no infrastructure to maintain yourself.
Before you can go down this path, though, you need to stop batching your data into slices for Cron to process, and rather publish the data event-by-event, and do continuous, rolling aggregations as necessary over some time windows
Related
I'm writing a web app in PHP + Laravel + MySQL.
In the system, a user can schedule emails (and other API calls) at arbitrary times (much like how you schedule posts in WordPress). I can use CRON to inspect the database every 5min or so to find emails that should be sent, send them, and update their status.
However, this is a SaaS app. So the amount of emails to be sent at a particular time can grow rapidly. I can create a "lock file" every time the CRON script runs so that only one instance of it is running at a time. The lock file will be deleted after a script finishes execution.
But with potentially large data, I would want a way to process multiple messages simultaneously, potentially using multiple "workers." Is there any existing solution manage such a queue?
Yes! Task/Message/Job queues are what you are looking for! They allow you to put various tasks in queues from which you can retrieve them and process them, this process can scale horizontally as each worker can pull a task once its finished with the previous one.
You should have the cron maybe every minute/two minutes that just uploads the task and what needs to be done. This will make sure the cron is very quick.
Take a look at Iron.io Here is an extract from the website which gives a nice overview of these kinds of systems:
An easy-to-use scalable task queue that gives cloud developers a
simple way to offload front-end tasks, run scheduled jobs, and process
tasks in the background and at scale.
Gearman is also a great solution that you can use yourself and is very simple. You can send the message in many different languages and use a different langauge to process it. Say PHP -> C etc...
The Wikipedia link will tell you everything you need to know, here is a quick excerpt:
Message queues provide an asynchronous communications protocol,
meaning that the sender and receiver of the message do not need to
interact with the message queue at the same time. Messages placed onto
the queue are stored until the recipient retrieves them.
I'm currently developing a php daemon for connecting and retreiving data from social networks like facebook and twitter. This script allready works but I have some concerns about it.
It's possible to create an infinite amount of accounts that the script has to process and (right now) it runs every 5 minutes to create a 'near' realtime experience. So my concern is that, when, let's say 5000 accounts, have been created and have to be monitored. The script slows down and maybe wil run longer than the 5 minute interval. Is there any way to work around this problem? And better, is there any good way (with php, possible with javascript) to create a better 'near' realtime experience?
Any advice will be great!
Thanks in advance
One option would be to spawn multiple daemons and share duties between them. Perhaps have single central job queue and have the daemons consume that. It's really a server-side issue and Javascript has very little to do with such tasks, as long it's not server-side JS.
If the number of monitored subjects is going into thousands, PHP is not really a viable choice since it's neither inherently multi-threaded nor does it have synchronization features. In mass monitoring scenarios, a dedicated server running a J2EE, .NET or a custom multithreaded application is pretty much a must.
for most sites you can retrieve a stream containing all that data(in real-time). For example:
1. twitter
site streams allows services,
such as web sites or mobile push
services, to receive real-time updates
for a large number of users without
any of the hassles of managing REST
API rate limits
2. Facebook
The Graph API supports real-time
updates to enable your application
using Facebook to subscribe to changes
in data from Facebook.
When using these streams you can process the streams in real-time and don't have to do no(nearly none) polling.
P.S: I would most definitely code this in node.js.
set the max execution time to zero and include it
enclose your script in a inite loop:
set_time_limit(0);
while(true){
/your code
}
You should however include some way to end the process gracefully.
Some popular ways to do this is by checking if a env var was set or if a specific file exists.
set_time_limit(0);
while(true){
/your code
if(file_exist(KILL_SWITCH_FILE))break;
}
Another approach would be setting a flag when(in a filem,in a sql database,...) that your script is running and removing it when your done.
That way you can check if another instance of your script is still running.
I am creating a web application using zend, here I create an interface from where user-A can send email to more than one user(s) & it works excellent but it slow the execution time because of which user-A wait too much for the "acknowledged response" ( which will show after the emails have sent. )
In Java there are "Threads" by which we can perform that task (send emails) & it does not slow the rest application.
Is there any technique in PHP/Zend just like in Java by which we can divide our tasks which could take much time eg: sending emails.
EDIT (thanks #Efazati, there seems to be new development in this direction)
http://php.net/manual/en/book.pthreads.php
Caution: (from here on the bottom):
pthreads was, and is, an experiment with pretty good results. Any of its limitations or features may change at any time; [...]
/EDIT
No threads in PHP!
The workaround is to store jobs in a queue (say rows in a table with the emails) and have a cronjob call your php script at a given interval (say 2 minutes) and poll for jobs. When jobs present fetch a few (depending on your php's install timeout) and send emails.
The main idea to defer execution:
main script adds jobs in the queue
cron script sends them in tiny slices
Gotchas:
make sure u don't send an email without deleting from queue (worst case would be if a user rescieves some spam at 2 mins interval ...)
make sure you don't delete a job without executing it first ...
handle bouncing email using a score algorithm
You could look into using multiple processes, such as with fork. The communication between them wouldn't be as simple as with threads (but then, it won't come with all of its pitfalls either), but if you're just sending emails, it might not be necessary to communicate much, if at all.
Watch out for doing forks on an Apache process. You may get some behaviors that you are not expecting. If you are looking to do any kind of asynchronous execution it should be via some kind of queuing mechanism. Gearman is one. Zend Server Job Queue is another. I have some demo code at Do you queue? Introduction to the Zend Server Job Queue. Cron can be used, but you'll have the problem of depending on your cron scheduler to run tasks whereas asynchronous computing often needs to be run immediately. Using a queuing system allows you to do that without threading.
There is a Threading extension being developed based on PThreads that looks promising at https://github.com/krakjoe/pthreads
There is pcntl, which allows you to create sub-processes, but php doesn't work very well for this kind of architecture. You're probably better off creating a long-running script (a daemon) and spawning multiple of them.
As of PHP there are no threads in it. However for php, you can have a look at this roundabout way
http://www.alternateinterior.com/2007/05/multi-threading-strategies-in-php.html
You may want to use a queue system for your email sending and send the email from another system which supports threads. PHP is just a tool and you should the tool that is best fitted for the job.
PHP doesn't include threading as part of the language, there are some methods that can emulate it but they aren't foolproof.
This Google search shows a few potential workarounds
I've a problem which is giving me some hard time trying to figure it out the ideal solution and, to better explain it, I'm going to expose my scenario here.
I've a server that will receive orders
from several clients. Each client will
submit a set of recurring tasks that
should be executed at some specified
intervals, eg.: client A submits task
AA that should be executed every
minute between 2009-12-31 and
2010-12-31; so if my math is right
that's about 525 600 operations in a
year, given more clients and tasks
it would be infeasible to let the server process all these tasks so I
came up with the idea of worker
machines. The server will be developed
on PHP.
Worker machines are just regular cheap
Windows-based computers that I'll
host on my home or at my workplace,
each worker will have a dedicated
Internet connection (with dynamic IPs)
and a UPS to avoid power outages. Each
worker will also query the server every
30 seconds or so via web service calls,
fetch the next pending job and process it.
Once the job is completed the worker will
submit the output to the server and request
a new job and so on ad infinitum. If
there is a need to scale the system I
should just set up a new worker and the
whole thing should run seamlessly.
The worker client will be developed
in PHP or Python.
At any given time my clients should be
able to log on to the server and check
the status of the tasks they ordered.
Now here is where the tricky part kicks in:
I must be able to reconstruct the
already processed tasks if for some
reason the server goes down.
The workers are not client-specific,
one worker should process jobs for
any given number of clients.
I've some doubts regarding the general database design and which technologies to use.
Originally I thought of using several SQLite databases and joining them all on the server but I can't figure out how I would group by clients to generate the job reports.
I've never actually worked with any of the following technologies: memcached, CouchDB, Hadoop and all the like, but I would like to know if any of these is suitable for my problem, and if yes which do you recommend for a newbie is "distributed computing" (or is this parallel?) like me. Please keep in mind that the workers have dynamic IPs.
Like I said before I'm also having trouble with the general database design, partly because I still haven't chosen any particular R(D)DBMS but one issue that I've and I think it's agnostic to the DBMS I choose is related to the queuing system... Should I precalculate all the absolute timestamps to a specific job and have a large set of timestamps, execute and flag them as complete in ascending order or should I have a more clever system like "when timestamp modulus 60 == 0 -> execute". The problem with this "clever" system is that some jobs will not be executed in order they should be because some workers could be waiting doing nothing while others are overloaded. What do you suggest?
PS: I'm not sure if the title and tags of this question properly reflect my problem and what I'm trying to do; if not please edit accordingly.
Thanks for your input!
#timdev:
The input will be a very small JSON encoded string, the output will also be a JSON enconded string but a bit larger (in the order of 1-5 KB).
The output will be computed using several available resources from the Web so the main bottleneck will probably be the bandwidth. Database writes may also be one - depending on the R(D)DBMS.
It looks like you're on the verge of recreating Gearman. Here's the introduction for Gearman:
Gearman provides a generic application
framework to farm out work to other
machines or processes that are better
suited to do the work. It allows you
to do work in parallel, to load
balance processing, and to call
functions between languages. It can be
used in a variety of applications,
from high-availability web sites to
the transport of database replication
events. In other words, it is the
nervous system for how distributed
processing communicates.
You can write both your client and the back-end worker code in PHP.
Re your question about a Gearman Server compiled for Windows: I don't think it's available in a neat package pre-built for Windows. Gearman is still a fairly young project and they may not have matured to the point of producing ready-to-run distributions for Windows.
Sun/MySQL employees Eric Day and Brian Aker gave a tutorial for Gearman at OSCON in July 2009, but their slides mention only Linux packages.
Here's a link to the Perl CPAN Testers project, that indicates that Gearman-Server can be built on Win32 using the Microsoft C compiler (cl.exe), and it passes tests: http://www.nntp.perl.org/group/perl.cpan.testers/2009/10/msg5521569.html But I'd guess you have to download source code and build it yourself.
Gearman seems like the perfect candidate for this scenario, you might even want to virtualize you windows machines to multiple worker nodes per machine depending on how much computing power you need.
Also the persistent queue system in gearman prevents jobs getting lost when a worker or the gearman server crashes. After a service restart the queue just continues where it has left off before crash/reboot, you don't have to take care of all this in your application and that is a big advantage and saves alot of time/code
Working out a custom solution might work but the advantages of gearman especially the persistent queue seem to me that this might very well be the best solution for you at the moment. I don't know about a windows binary for gearman though but i think it should be possible.
A simpler solution would be to have a single database with multiple php-nodes connected. If you use a proper RDBMS (MSql + InnoDB will do), you can have one table act as a queue. Each worker will then pull tasks from that to work on and write it back into the database upon completion, using transactions and locking to synchronise. This depends a bit on the size of input/output data. If it's large, this may not be the best scheme.
I would avoid sqlite for this sort of task, although it is a very wonderful database for small apps, it does not handle concurrency very well, it has only one locking strategey which is to lock the entire database and keep it locked until a sinlge transaction is complete.
Consider Postgres which has industrial strength concurrency and lock management and can handle multiple simultanious transactions very nicely.
Also this sounds like a job for queuing! If you were in hte Java world I would recommend a JMS based archictecture for your solution. There is a 'dropr' project to do something similar in php but its all fairly new so it might not be suitable for your project.
Whichever technoligy you use you should go for a "free market" solution where the worker threads consume available "jobs" as fast as they can, rather than a "command economy" where a central process allocates tasks to choosen workers.
The setup of a master server and several workers looks right in your case.
On the master server I would install MySQL (Percona InnoDB version is stable and fast) in master-master replication so you won't have a single point of failure.
The master server will host an API which the workers will pull at every N seconds. The master will check if there is a job available, if so it has to flag that the job has been assigned to the worker X and return the appropriate input to the worker (all of this via HTTP).
Also, here you can store all the script files of the workers.
On the workers, I would strongly suggest you to install a Linux distro. On Linux it's easier to set up scheduled tasks and in general I think it's more appropriate for the job.
With Linux you can even create a live cd or iso image with a perfectly configured worker and install it fast and easy on all the machines you want.
Then set up a cron job that will RSync with the master server to update/modify the scripts. In this way you will change the files in just one place (the master server) and all the workers will get the updates.
In this configuration you don't care of the IPs or the number of workers because the workers are connecting to the master, not vice-versa.
The worker job is pretty easy: ask the API for a job, do it, send back the result via API. Rinse and repeat :-)
Rather than re-inventing the queuing wheel via SQL, you could use a messaging system like RabbitMQ or ActiveMQ as the core of your system. Each of these systems provides the AMQP protocol and has hard-disk backed queues. On the server you have one application that pushes new jobs into a "worker" queue according to your schedule and another that writes results from a "result" queue into the database (or acts on it some other way).
All the workers connect to RabbitMQ or ActiveMQ. They pop the work off the work queue, do the job and put the response into another queue. After they have done that, they ACK the original job request to say "its done". If a worker drops its connection, the job will be restored to the queue so another worker can do it.
Everything other than the queues (job descriptions, client details, completed work) can be stored in the database. But anything realtime should be put somewhere else. In my own work I'm streaming live power usage data and having many people hitting the database to poll it is a bad idea. I've written about live data in my system.
I think you're going in the right direction with a master job distributor and workers. I would have them communicate via HTTP.
I would choose C, C++, or Java to be clients, as they have capabilities to run scripts (execvp in C, System.Desktop.something in Java). Jobs could just be the name of a script and arguments to that script. You can have the clients return a status on the jobs. If the jobs failed, you could retry them. You can have the clients poll for jobs every minute (or every x seconds and make the server sort out the jobs)
PHP would work for the server.
MySQL would work fine for the database. I would just make two timestamps: start and end. On the server, I would look for WHEN SECONDS==0
I'm working an image processing website, instead of having lengthy jobs hold up the users browser I want all commands to return fast with a job id and have a background task do the actual work. The id could then be used to check for status and results (ie a url of the processed image). I've found a lot of distributed queue managers for ruby, java and python but I don't know nearly enough of any of those languages to be able to use them.
My own tests have been with shared mysql database to queue jobs, lock them to a worker, and mark them as completed (saving the return data in the db). It was just a messy prototype, and the entire time I felt as if I was reinventing the wheel (and not very elegantly). Does something exist in php (or that I can talk to RESTfully?) that I could use?
Reading around a bit more, I've found that what I'm looking for is a queuing system that has a php api, it doesn't have to be written in php. I've only found classes for use with Amazon's SQS, but not only is that not free, it's also quite latent sometimes (over a minute for a message to show up).
Have you tried ActiveMQ? It makes mention of supporting PHP via the Stomp protocol. Details are available on the activemq site.
I've gotten a lot of mileage out of the database approach your describing though, so I wouldn't worry too much about it.
Do you have full control over server?
MySQL queue could be fine in such case. Have a PHP script that is running constantly (in endless while loop), querying the MySQL database for new "tasks" and sleep()ing in between to reduce the load in idle time.
When each task is completed, mark it in the database and move to the next one.
To prevent that whole thing stops if your script crashes/exists (PHP memory overflow, etc.) you can, for example, place it in inittab (if you use Linux as a server) and init will restart it automatically.
Zend_Framework has a queue class, with a number of implementations of Mysql-backed, SQS and some other back-ends.
Personally, I've had excellent results with BeanstalkD recently, which also has a PHP client. I'm just serialising some data with JSON to throw into it, which gets decoded and run on the worker(s).