I have a web application dedicated to batch processing (batch service here on out, api driven) and I have the main web application that is dedicated to everything else. I've been struggling with making a decision on what the best way is to avoid duplication of business logic in the batch service. Both applications are clustered. The separation for batch processing has been okay for simple jobs, but I have more complex jobs where it would just cause chaos if the business logic were duplicated. Here's my use case for the purposes of this question.
Customer schedules a cron job for user updates.
Batch service is given a CSV file with 20,000 user records.
The batch service rips through the file performing validation on the records, basically a dry run.
The batch service will check the allowable change and error thresholds (percentages are counts)
If validation thresholds pass, the batch service will begin creating/updating users.
When users are created or updated, there are a number of modules/features that need to know about these events.
Job progress is tracked and customer can view progress, logs, and status of job.
Here are a few solutions I have been thinking about:
Jar up the business logic and share it across the two applications. This wouldn't necessarily be easy because the main application is a Grails application and it's got GORM littered throughout.
Have the batch service hit APIs on the main application for the create and updates and possibly the more complex validation scenarios. Worried about the toll this would take on tomcat, but calls would be going through the load balancer so they would be distributed.
Have the batch service hit APIs on the main application for validation, then queue create/update requests and let the main application retrieve them. Same as above, queue would help reduce http calls. Also would need a queue to report status back to batch service.
Duplicate some logic by having batch service do it's own validation and inserts/updates, but then fire a user created event or user updated event so modules/features in the main app can deal with the changes.
Embed the batch processing service into the main application
Other details:
The batch service and web application are both clustered
Both are running on AWS, so I have tools like SQS and SNS easily accessible
Java 1.7 applications
Tomcat containers
Main application is Grails
Batch service uses Spring Batch and Quartz at it's core
So my question is what are accepted ways to avoid duplication of business logic based on the details above? Can/Should the architecture be changed to better accommodate this?
Another idea to consider is what would this look like and a "microservices" architecture. That word has been tossed around a number of times in the office and we have been considering the idea of breaking up the main web application into services. So for example, we may end up with a service for user management.
Say for example you are using a Java EE 6 application.
Your CSV batch updater could be nothing more than a Timer that every once in a while reads a CSV file dumped in a folder and for each user update encoded on that file pumps a message to a queue encoding the update you want to do.
Somewhere else, you have a message driven bean that reacts to the update request message and triggers the update business logic for the user reported on the JMS message.
After the transaction is committed successfuly, if you have ten differn application that are interested in knowing that the user was updated, you could post a message to, for example, a notification topic with - say - messageType='userUpdated'.
Each of your 10 applications that cares about this could be a consumer on this topic.
They would be informed that a user was updated and maybe internally publish a local event (e.g. a CDI event - a guava event - whatever - and the internal satke holders would now of it).
Normally, there are always Java EE replacements in every technlogy stack.
Every decent technology stack offers ways to promote loose coupling between UI and business logic, precisely so that HTML / WEB is just viewed as one of many entry points to an application's business logic.
In scala, i there is an AKKA framework that looks super interesting.
The point is, as long as your business logic is not written in some place that only the web application can tap into, your fine. Otherwise, you've made the design decision to couple your business logic with UI.
In your case, I would suggest to make a separation by concern, I mean a plugin that gathers only the domain classes if using Grails, the other plugins that take care of Services ... these would represent the application core, I think it's much easier this way if your application contain too much KLOC, using microservices will take you time too much time if you have a lot of calls between modules.
Communication between functional modules aka. plugins can be made via events, see events-si or rabbit MQ plugin.
Related
I have a terminal server monitor project. In the backend, I use the Spring MVC, MyBatis and PostgreSQL. Basically I query the session information from DB and send back to front-end and display it to users. But there is some large queries(like searching total users, total sessions, etc.), which slow down the system when user opens the website, So I want to do these queries as asynchronous tasks so the website could be opened fast rather than waiting for the query. Also, I would check terminal server state periodically from DB(every hour), and if terminal server fails or average load is too high, I would notifying admins. I do not know what should I use, maybe AKKA, or any other way to do these two jobs(1.do the large query asynchronously 2. do some periodical query)? Please help me, thanks!
You can achieve this using Spring and caching where necessary.
If the data you're displaying is not required to be "in real-time", but it can be "near real-time" you can read the data from the DB periodically and cache it. Your app then reads from the cache.
There's different approaches you can explore.
You can try to create a materialized view in PostgreSQL which will hold the statistic data you need. Depending on your requirements you have to see how to handle refresh intervals etc.
Another approach is to use application level cache - you can leverage Spring for that(Spring docs). You can populate the cache on start up and refresh it as necessary.
The task that runs every hour can be implemented again leveraging Spring (Spring docs) #Scheduled annotation.
To answer your question - don't use Akka - you have all the tools necessary to achieve the task in the Spring ecosystem.
Akka is not very relevant here, it is for event-driven programming model which deals with concurrency issues to build highly scalable multithreaded applications.
You can use Spring task scheduler for running heavy queries periodically. If you want to keep it simple, you can solve your problem by simply storing the data like total users, total sessions etc, in the global application context. And periodically update this data from database using spring scheduler. You can also store the same in a separate database table, so that this data can be easily loaded at the initialization time.
I really don't see why you need "memcached", "materialized views", "Websockets" and other heavy technologies and frameworks, for a caching a small set of data. All you need is maintain a set of global parameters in your application context, keep them updated using a scheduled task as frequently as desired.
For my master's degree final project I decided to design a drone delivery system. The main purpose is to learn to design complex systems.
The basic use case is this:
User goes to merchant online shop, selects the products, selects the delivery method as "Drone delivery" and selects his delivery location.
Merchant website, makes an API call to our drone delivery system (DDS) application to register the new delivery order.(The order will contain all information that we need: parcel pick up location, and destination location...)
The DDS application based on drones positions, and based on an algorithm will calculate and mark which drone can deliver this order in the shortest time.
The selected drone when is free will deliver the order.
So far so good. My questions are related to the software architecture of this system. I have some general questions and some specific questions.
General questions:
How do you design a system like this in order to be scalable? I mean: The system may be used by may merchants, if they hit my API in the same time with 100 orders, the system must be able to handle it.
What are some good design principles or patterns when designing an system like this?
Specific questions:
So far i have came up with this architecture:
System Components:
Java(Spring) application
Rest web servce
web interface managing dorens and parces
bussines logic and algorithms for routing drones
producer/consumer for RabbitMQ
Mysql Server
RabbitMq
System flow:
Merchant hits REST API to register the order
The Java Application saves the order to Mysql database.
After saving the order to the database, an Producer puts the order in a queue in RabbitMQ
An Consumer consumes the RabbitMQ order queue. It takes each order and calculates based on an algorithm the drone that offers the best time for the delivery. Each drone has a separate queue in RabbitMQ. After finding the best drone, the consumer inserts the order in the drone queue in RabbitMQ. The consumer also interrogates the mysql database during this process.
Whenever a drone is free, it will communicate with the system to ask for the next order. The system will look in the drone RabbitMQ queue and will take from there the next order.
My questions are related to the consumer and producer:
Is OK that the consumer to have logic in it, in my example it will have the algorithm that will determine the best drone, to do this it needs to talk to mysql also, for retrieving drone positions? Is this a good practice? If not how can i do different?
Is best practice for the consumer to stay in the application? Right now consumers are running in the same server as the web service and the code is not separated from web service code. I am thinking maybe in the future you may need to move the consumers in a separate server? How do you think the consumers so they can easily be separated from the application?
I think that the producer must stay in the application, i mean is coupled with the web service app. Is that OK?
Sorry for the long post, and for my poor English.
Thank you very much :)
Yes, the consumer should have logic in it. This is a standard EIP routing pattern.
If you properly separate your business logic layers from your data access layers (your queue access is a data access layer), then it probably isn't a problem to have them all share a common project. You ultimately probably want to separate your business logic/domain model from the web service and the router/consumer, but those are much more deployment and packaging concerns.
As long as you keep your web service code out of your business logic (and vice versa) you will probably be ok, you will just have to deploy the whole thing multiple times, and only expose the endpoints that are relevant for any given deployment. You ultimately might be happier though if you separate your layers via libraries, as it will actually enforce not mixing the concerns.
And yes, the producer must be deployed with the web service, just make sure you are aware that as a Data Access Layer, that it's in a separate package/class. It will make your testing much easier.
I'm developing an MVC spring web app, and I would like to store the actions of my users (what they click on, etc.) in a database for offline analysis. Let's say an action is a tuple (long userId, long actionId, Date timestamp). I'm not specifically interested in the actions of my users, but I take this as an example.
I expect a lot of actions by a lot of (different) users par minutes (seconds). Hence the processing time is crucial.
In my current implementation, I've defined a datasource with a connection pool to store the actions in a database. I call a service from the request method of a controller, and this service calls a DAO which saves the action into the database.
This implementation is not efficient because it waits that the call from the controller and all the way down to the database is done to return the response to the user. Therefore I was thinking of wrapping this "action saving" into a thread, so that the response to the user is faster. The thread does not need to be finished to get the reponse.
I've no experience in these massive, concurrent and time-critical applications. So any feedback/comments would be very helpful.
Now my questions are:
How would you design such system?
would you implement a service and then wrap it into a thread called at every action?
What should I use?
I checked spring Batch, and this JobLauncher, but I'm not sure if it is the right thing for me.
What happen when there are concurrent accesses at the controller, the service, the DAO and the datasource level?
In more general terms, what are the best practices for designing such applications?
Thank you for your help!
Take a singleton object # apps level and update it with every user action.
This singleton object should have a Hashmap as generic, which should get refreshed periodically say after it reached a threshhold level of 10000 counts and save it to DB, as a spring batch.
Also, periodically, refresh it / clean it upto the last no.# of the records everytime it processed. We can also do a re-initialization of the singleton instance , weekly/ monthly. Remember, this might lead to an issue of updating the same in case, your apps is deployed into multiple JVM. So, you need to implement the clone not supported exception in singleton.
Here's what I did for that :
Used aspectJ to mark all the actions of the user I wanted to collect.
Then I sent this to log4j with an asynchronous dbAppender...
This lets you turn it on or off with log4j logging level.
works perfectly.
If you are interested in the actions your users take, you should be able to figure that out from the HTTP requests they send, so you might be better off logging the incoming requests in an Apache webserver that forwards to your application server. Putting a cluster of web servers in front of application servers is a typical practice (they're good for serving static content) and they are usually logging requests anyway. That way the logging will be fast, your application will not have to deal with it, and the biggest work will be writing a script to slurp the logs into a database where you can do analysis.
Typically it is considered bad form to spawn your own threads in a Java EE application.
A better approach would be to write to a local queue via JMS and then have a separate component, e.g., a message driven bean (pretty easy with EJB or Spring) which persists it to the database.
Another approach would be to just write to a log file and then have a process read the log file and write to the database once a day or whenever.
The things to consider are: -
How up-to-date do you need the information to be?
How critical is the information, can you lose some?
How reliable does the order need to be?
All of these will factor into how many threads you have processing your queue/log file, whether you need a persistent JMS queue and whether you should have the processing occur on a remote system to your main container.
Hope this answers your questions.
In my environment I need to schedule long-running task. I have application A which just shows to the client the list of currently running tasks and allows to schedule new ones. There is also application B which does the actual hard work.
So app A needs to schedule a task in app B. The only thing they have in common is the database. The simplest thing to do seems to be adding a table with a list of tasks and having app B query that table every once in a while and execute newly scheduled tasks.
Yet, it doesn't seem to be the proper way of doing it. At first glance it seems that the tool for the job in an enterprise environment is a message queue. App A sends a message with task description to the queue, app B reads a message from the queue and executes the task. Is it possible in such case for app A to get the status of all the tasks scheduled (persistent queue?) without creating a table like the one mentioned above to which app B would write the status of completed tasks? Note also that there may be multiple instances of app A and each of them needs to know about all tasks of all instances.
The disadvantage of the 'table approach' is that I need to have DB polling.
The disadvantage of the 'message queue approach' is that I'm introducing a new communication channel into the infrastructure (yet another thing that can fail).
What do you think? Any other ideas?
Thank you in advance for any advice :)
========== UPDATE ==========
Eventually I decided on the following approach: there are two sides of this problem: one is communication between A and B. The other is getting information about the tasks.
For communication the right tool for the job is JMS. For getting data the right tool is the database.
So I'll have app A add a new row to the 'tasks' table descibing a task (I can query this table later on to get list of all tasks). Then A will send a message to B via JMS just to say 'you have work to do'. B will do the work and update task status in the table.
Thank you for all responses!
You need to think about your deployment environment both now and likely changes in the future.
You're effectively looking at two problems, both which can be solved in several ways, depending on how much infrastructure you able to obtain and are also willing to introduce, but it's also important to "right size" your design for your problems.
Whilst you're correct to think about the use of both databases and messaging, you need to consider whether these items are overkill for your domain and only you and others who know your domain can really answer that.
My advice would be to look at what is already in use in your area. If you already have database infrastructure that you can build into, then monitoring task activity and scheduling jobs in a database are not a bad idea. However, if you would have to run your own database, get new hardware, don't have sufficient support resources then introduction of a database may not be a sensible option and you could look at a simpler, but potentially more fragile approach of having your processes write files to schedule jobs and report tasks.
At the same time, don't look at the introduction of a DB or JMS as inherently error prone. Correctly implemented they are stable and proven technologies that will make your system scalable and manageable.
As #kan says, use exposing an web service interface is also a useful option.
Another option is to make the B as a service, e.g. expose control and status interfaces as REST or SOAP interfaces. In this case the A will just be as a client application of the B. The B stores its state in the database. The A is a stateless application which just communicates with B.
BTW, using Spring Remote you could expose an interface and use any of JMS, REST, SOAP or RMI as a transport layer which could be changed later if necessary.
You have messages (JMS) in enterprise architecture. Use these, they are available in Java EE containers like Glassfish. Messages can be serialized to be sure they will be delivered even if the server reboots while they are in the queue. And you even do not need to care how all this is implemented.
There can be couple of approaches here. First, as #kan suggested to have app B expose some web service for the interactions. This will heterogenous clients to communicate with app B. Seems a good approach. App B can internally use whatever persistent store it deems fit.
Alternatively, you can have app B expose some management interface via JMX and have applications like app A talk to app B through this management interface. Implementing the task submission and retrieving the statistics etc. would be simpler. Additionally, you can also leverage JMX notifications for real time updates on task submissions and accomplishments etc. Downside to this is that this would be a Java specific solution and hence supporting heterogenous clients will be distant dream.
I am looking for a pattern and/or framework which can model the following problem in an easily configurable way.
Every say 3 minutes, I needs to have a set of jobs kick off in a web application context that will concurrently hit web services to obtain the latest version of data, and push it off to a database. The problem is the database will be being heavily used to read the data from to do tons of complex calculations on the data. We are currently using spring so I have been looking at Spring Batch to run this process does anyone have any suggestions/patterns/examples of using Spring or other technologies of a similar system?
We have used ServletContextlisteners to kick off TimerTasks in our web applications when we needed processes to run repeatedly. The ServletContextListener kicks off when the app server starts the application or when the application is restarted. Then the timer tasks act like a separate thread that repeats your code for the specified period of time.
ServletContextListener
http://www.javabeat.net/examples/2009/02/26/servletcontextlistener-example/
TimerTask
http://enos.itcollege.ee/~jpoial/docs/tutorial/essential/threads/timer.html
Is refactoring the job out of the web application and into a standalone app a possibility?
That way you could stick the batch job onto a separate batch server (so that the extra load of the batch job wouldn't impact your web application), which then calls the web services and updates the database. The job can then be kicked off using something like cron or Autosys.
We're using Spring-Batch for exactly this purpose.
The database design would also depend on what the batched data is used for. If it is for reporting purposes, I would recommend separating the operational database from the reporting database, using a database link to obtain the required data from the operational database into the reporting database and then running the complex queries on the reporting database. That way the load is shifted off the operational database.
I think it's worth also looking into frameworks like camel-integration. Also take a look at the so called Enterprise Integration Patterns. Check the catalog - it might provide you with some useful vocabulary to think about the scaling/scheduling problem at hand.
The framework itself integrates really well with Spring.