I am trying to understand Serverless architecture which says 2 distinct things:
you as an app developer think about your function only and not about the server responsibilities. Well, the server still has got to be somewhere. By servers, I understand here that its mean both:
on the infrastructure side Physical Server/VM/container
as well as the on the software side: say, Tomcat
Now, I have worked on Cloud Foundry and studied the ER i.e. Diego Architecture of Cloud Foundry and the buildpack and open Service Broker API facility of Cloud foundry. Effectively, Cloud Foundry also already works on a "similar" model where the application developer focuses on his code and the deployment model with the help of buildpack prepares a droplet with the needed Java runtime and Tomcat runtime and then uses it to create a garden container that serves user requests. So, the developer does not have to worry about where the Tomcat server or the VM/container will come from. So, aren't we already meeting that mandate in Cloud Foundry?
your code comes into existence for the duration of execution and then dies. This I agree is different from the apps/microserevices that we write in Cloud Foundry in that they are long running server processes instead. Now, if I were to develop a Java webapp/microservice with 3 REST endpoints (myapp/resource1, myapp/resource2, myapp/resource3) possibly on a Tomcat Web Server, I need:
a physical machine or a VM or a container,
the Java runtime
the Tomcat container to be able to run my war file.
Going by what Serverless suggests, I infer I am supposed to concentrate only on the very specific function say handling the request to myapp/resource1. Now, in such a scenario:
What is my corresponding Java class supposed to look like?
Where do I get access to the J2EE objects like HttpServletRequest or HttpServletResponse objects and other http or servlet or JAX-RS or Spring MVC provided objects that are created by the Tomcat runtime?
Is my Java class executed within a container that is created for the duration of execution and then destroyed after execution? If yes, who manages the creation/destruction of such a container?
Would Tomcat even be required? Is there an altogether different generic way of handling requests to these three REST endpoints? Is it somewhat like httpd servers using python/Java CGI scripts to handle http requests?
Related
We have developed a custom JAX-WS application that essentially achieves two things.
Exposes a few web service methods to perform some functionality.
Utilizes org.quartz.Scheduler to schedule and execute some polling tasks that monitors and processes data on a few database tables. (The logic here is slightly complex, hence a custom application was chosen over the use of WSO2 DSS)
This application is uploaded on WSO2 AS 5.2.1 and runs quite seamlessly. However, I'm unsure what will happen if we have to cluster the AS application server. Logically, I would think that each node will have its own instance of the custom application running within it, and hence its own scheduler. Would this not increase the risk of processing the same record, across both instances. Is my interpretation of the above scenario correct, from a clustering perspective?
Yes.You are correct.In cluster of app server nodes each nodes will have its own instance of the application.In your case each node will have seperate scheduler.You may consider using tasks from ESB 4.9.0. there WSO2 has added coordination support to work in cluster environment.
I learned about service oriented architecture yesterday, and I have a question about it.
in order to talk to web service provider the initial communication has to be started by a service consumer. Then does it mean that a web service provider cannot talk to another web service directly (because it is not a consumer)?
I do not have enough information to grasp a full scope of what you're getting at exactly. However, I can say that this statement:
Then does it mean that a web service provider cannot talk to another web service directly (because it is not a consumer)
Isn't really true. A program can (programmatically) access data provided by a web service. The web service has no real awareness as to what a 'consumer' is. It only sees (programmatically) the data provided by the client (typically browser data, cookies, cache, etc..). But that doesn't stop anyone from opening a bash shell and curling the website.
This will retrieve any data statically provided by the server. Note that the data may obfuscated using JavaScript as to take measures to prevent any programs outside of a browser environment to access their critical data.
So the answer to that question, is yes and no.
You should ask this question on https://softwareengineering.stackexchange.com/ as it is more relevant to questions regarding programming concepts.
Both from technical and architectural points of view service of course can call another one. Simply, it is changing its role to behave as a consumer for the second service. Just be aware that things may become messy if both services are calling each other both ways to finish their task for a single client request. Though there are often valid scenarios for such behaviour, if both services are managed by the same entity, its worth looking if tasks shouldn't be moved or services merged as this may be a sign of a bad design decisions.
Any piece of software can talk to a web service as long as it can reach it.
My application it's C++ service. And I need to add API for it. I consider that it will be XML/JSON RPC based API. How should I design a program for reusing existing code base and provide API.
I see following options:
My application will work via RPC layer. Seems that it's bad option due to low performance;
Before starting of service I will fork it and run my application in the first process and RPC server in the second; Seems ok, but how to restart RPC server in this case?
I guess there is a well known pattern for such issues.
Thanks.
If you can use a web server, then the FastCGI concept might be what you're looking for. One of the main duties of FastCGI is to allow you to put on a public API (from the web server) that internally calls the "real" application, in your case the resident C++ service. So all work is done at the web server to create the public API using any technology you wish, and little or no code changes done in your C++ service.
I have a web application mostly written by others based on JSF 2, Mybatis, Spring 3 and tens of other libraries, running on Weblogic, it works and now I have to create a distinct command line application to schedule the running of some tasks already present in the web app.
I added a class with a main method in order to maintain only one codebase with a different build process to generate an executable JAR instead of a WAR. Using Spring's ClassPathXmlApplicationContext I managed to recreate the web application context, access the database beans and use them, but I'm stuck with a WSRR call which fails.
The commands:
GraphQuery graphQuery =
(GraphQuery)DataFactory.INSTANCE.create(TypeConstants.SR_URI, TypeConstants.TYPE_GRAPHQUERY);
graphQuery.setQueryExpression("/WSRR/GenericObject[#CFT_APPLIC='DS" + param + "']");
fail with a long stack, having the root exception
Caused by: java.lang.NullPointerException
at java.util.ResourceBundle.getBundle(ResourceBundle.java:960)
at com.ibm.ws.webservices.engine.resources.ProjectResourceBundle$Context.loadBundle(ProjectResourceBundle.java:474)
at com.ibm.ws.webservices.engine.resources.ProjectResourceBundle.getBundle(ProjectResourceBundle.java:372)
at com.ibm.ws.webservices.engine.resources.ProjectResourceBundle.getBundle(ProjectResourceBundle.java:341)
at com.ibm.ws.webservices.engine.resources.MessagesConstants.<clinit>(MessagesConstants.java:93)
I found that some classes and configurations are provided at runtime by the application server, and have no idea about how to replace them outside the application server.
The IBM redbook says (pages 120-121) that is possible to access a web service using a Java client, but requires a suitable EJB runtime.
How can I replicate needed EJB parameters outside the application server? I tried to use the Eclipse debugger to follow the execution of the application and extract them, but it fails, probably because the classes are loaded by Weblogic classloader.
We have a C++ (SOAP-based) web service deployed Using Systinet C++ Server, that has a single port for all the incoming connections from Java front-end.
However recently in production environment when it was tested with around 150 connections, the service went down and hence I wonder how to achieve load-balancing in a C++ SOAP-based web service?
The service is accessed as SOAP/HTTP?
Then you create several instances of you services and put some kind of router between your clients and the web service to distribute the requests across the instances. Often people use dedicated hardware routers for that purpose.
Note that this is often not truly load "balancing", in that the router can be pretty dumb, for example just using a simple round-robin alrgorithm. Such simple appraoches can be pretty effective.
I hope that your services are stateless, that simplifies things. If indiviual clients must maintain affinity to a particualr instance thing get a little tricker.