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You are not a financial expert ? Deploying several instance and polyglot verticles. Task – Composing methods returning Single. That’s a pretty good question, and probably a good start. If you go on the Vert.
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This description is rather unclear, right? This lab offers attendees an intro-level, hands-on session with Vert. How to develop microservices with Vert. How to expose HTTP endpoints with Vert. How to use databases with Vert. We will attempt to explain Vert. Remember that we said in the previous section that Vert.
There are a three important points in this description: toolkit, reactive and “on the JVM”. How does this impact you and your application? Therefore, to use the awesomeness provided by Vert. It is specifically made to build reactive applications, or more appropriately, systems. Elastic: a reactive system must stay responsive under various loads. As a consequence, it must scale up and down, and be able to handle the load with minimal resources. Message driven: components from a reactive system interacts using asynchronous message-passing.
Events are delivered in an event loop that must never be blocked. Unlike traditional, let’s say “enterprise”, systems, Vert. Some of these threads are event loops, they are responsible for dispatching the events in Handlers. If you block this thread, the events won’t be delivered anymore. When the response has been received, the same event loop calls the callback. We can even mix and match any combination of all these languages. With the event bus, you send messages to addresses.
However, you might still want to ask: What kind of applications can I use Vert. REST microservices, high volume event processing or a full blown backend message-bus application, Vert. It’s fast, and does not constraint you. The microservice architectural style is an approach to developing a single application as a suite of small services, each running in its own process and communicating with lightweight mechanisms, often an HTTP resource API. These services are built around business capabilities and independently deployable by fully automated deployment machinery. Microservice is an architectural style, which means it is a specialization of element and relation types, together with constraints and how they can be used . I believe by now, I have left you more confused than you before we started.
Let’s imagine, we have an application, rather large. 50-steps process and be validated by 5 levels of management. In this lab, we won’t address point 5, but you should know that Vert. You can employ whatever technology best suites your environment. Point 6, however, is interesting, and often misunderstood. It’s pretty cool to develop independent pieces of software that magically interact at runtime.
Yes, I said magically but in technology we don’t believe in magic. To make this happen, what we need is some form of service discovery at runtime. The service discovery mechanism can achieve it’s goal with any number of suitable means. Having a service discovery mechanism allows our system components interact transparently amongst each other regardless of location or environment. Although by definition, microservice applications are not required to be distributed, there usually are in practice. CAP theorem, consistency, monitoring, and many other reasons to fail.
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So microservices applications need to be designed to accommodate failures from their early implementation stage. Before we go further, there are a couple of points I would like to mention. Microservices are not new and the concept is not rocket science. Also very important point to understand is: microservices are not a silver bullet.
The major concerns when it comes microservices are rapid delivery, adaptation, independence and replaceability. If you have been a developer for about 10 years, you might want to ask what difference is between microservices and SOA. For a lot of people it’s about size. This is not always true because services don’t necessarily have to be small which makes the term “microservice” quite misleading.
Both approaches inherit from the service oriented computing, aiming to decompose and manage independent pieces of software. You may have never heard about this even if you used it: COM, Corba, Jini, OSGi, and web services are all different implementations of service oriented computing. Finally, there is a common misconception that microservices must be RESTful by nature. This can’t be farther from the truth. Microservices can employ any number interaction style that best fit their purpose: RPC, events, messages, streams etc. In this lab we will using RESTful services, async RPC, and message sources. The market data is published on the Vert.
The traders – these are a set of components that receives quotes from the quote generator and decides whether or not to buy or sell a particular share. To make this decision, they rely on another component called the portfolio service. The portfolio – this service manages the number of shares in our portfolio and their monetary value. It is exposed as a service proxy, i. RPC service on top of the Vert. For every successful operation, it sends a message on the event bus describing the operation.
It uses the quote generator to evaluate the current value of the portfolio. The audit component receives operations from the portfolio service via an event bus and address . It then stores theses in a database. It also provides a REST endpoint to retrieve the latest set of operations. The dashboard – some UI to let us know when we become rich. The dashboard presents the available services, the value of each company’s quotes, the latest set of operations made by our traders and the current state of our portfolio.
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It also shows the state of the different circuit breakers. We are going to implement critical parts of this application. However, the rest of the code is provided to illustrate some other Vert. But before we start, we need to install a couple of software on our machine. You can use either Oracle JDK or OpenJDK.
Unzip to a directory of your choice and add it to the PATH. You can use Eclipse, IntelliJ or Netbeans. If you don’t have an IDE, here are the step to get started with Eclipse. First download Eclipse from the download page. In the Eclipse Package list, select Eclipse IDE for Java Developers.
It brings you to a download page with a Download button. In the destination directory, you should find an Eclipse binary that you can execute. Eclipse asks you to create a workspace. You can import the code in your IDE as a Maven project. You can refer to your IDE documentation to know how to import Maven projects.
A complete solution is given in the solution directory. If you remember the microservice section, we need some service discovery mechanism. To let every component discover the services, it needs to store the service record in a location that every one can access. So, when you start your Vert. In our context, you don’t need to configure anything. The lab provides a cluster configuration using unicast and the 127.
The cluster is built on top of Hazelcast. It creates a über-jar containing your application and all its dependencies, including Vert. Wait, I told you that Vert. This Launcher class creates the Vert.
Again, it’s just a convenient way, you can use your own main class. Verticles is a way to structure Vert. It’s not mandatory, but it is quite convenient. A verticle is a chunk of code that is deployed on top of a Vert.
A verticle has access to the instance of vertx on which it’s deployed, and can deploy other verticles. Deploy the verticle with a configuration. Here it gets the details about the companies to simulate. JSON, so you are going to see a lot of JSON in this lab. For each company found in the configuration, it deploys another verticle with the extracted configuration. Finally, it deploys another verticle providing a very simple HTTP API.
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The last part of the method is about the service discovery mentioned in the microservice section. This component generates quotes sent on the event bus. ADDRESS is the event bus address on which the messages are sent. Asynchronous methods have a Handler as last parameter that is invoked when the operation has been completed. As the previous service, it needs to be published. Handlers are an important part of Vert.
The message parameter is the received message. This handler does not receive messages from the event bus, but HTTP requests. The response to a request is accessible using request. To write the response use response.
To create the JSON representation of an object, you can use the Json. You may wonder why synchronization is not required. Indeed we write in the map and read from it without any synchronization constructs. Here is one of the main feature of Vert. The main class we used creates a clustered Vert. 90000, “shares” : 45889, “symbol” : “BCT”, “name” : “Black Coat”, “ask” : 654.
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500000, “shares” : 251415, “symbol” : “DVN”, “name” : “Divinator”, “ask” : 877. It gives the current details of each quotes. Neither am I, and this is a overly simplified version. You can check Wikipedia for more details. In the portfolio component, we are going to implement an event bus service. A Portfolio stores the owned shares and the available cash. They can be exposed using any types of interactions, and Remote Procedure Calls is one of them.
With RPC, a component can effectively send a request to another component by doing a local procedure call, which results in the request being packaged in a message and sent to the callee. However, it also introduces a tighter coupling between the caller and the callee. Traditional RPC exhibits an annoying drawback: the caller waits until the response has been received. This is definitely a blocking call, as it involves at least two network messages. In addition, it is not really designed for failures while distributed communications have many reasons to fail.
Async RPC follows the same principles as RPC, but instead of waiting for the response, it passes a Handler called when the result is received. Upon success, the handler can retrieve the result. This method lets you retrieve a Portfolio object. The other methods follows the same pattern.
You may have also noticed that the package has a package-info. This file is required to enable the service proxy generation. Portfolio class to see how it looks like. As you can see, all the JSON handling is managed by converters that are automatically generated, so a data object is very close to a simple bean.
A Future represents the result of an action that may, or may not, have occurred yet. The result may be null if the Future is used to detect the completion of an operation. The operation behind a Future object may succeed or fail. You access the event bus using vertx. We have provided the buy and sell methods, that are just doing some checks before buying or selling shares. Once the action is emitted, we send a message on the event bus that will be consumed by the Audit Service and the Dashboard.
So, we are going to use the publish method. This method computes the current value of the portfolio. That’s a bit more tricky, so let’s do it step by step. We published in in the previous section. So, let’s start to get this service. Fill the evaluate method to retrieve the quotes service.
The name of the service is quotes. If you can’t retrieve the service, just passed a failed async result to the handler. Get the HTTP Client for the requested service. Write the content of this method.
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You would need to create a Future object to report the completion of the operation. This future is the “returned” result of the method. Once the value is computed, complete the future. Don’t forget to report failures to the future too. First we need a verticle that creates the actual service object, registers the service on the event bus and publishes the service in the service discovery infrastructure. Publish it using the service discovery discovery.
We have a second service to publish. Remember, we are also sending messages on the event bus when we buy or sell shares. At the end of the start method, write the code required to publish the portfolio-events service. EVENT_ADDRESS is the event bus address. Now we are done, and it’s time to build and run this service.
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Here you go, the portfolio service is started. It discovers the quotes service and is ready to be used. Go back to the dashboard, and you should see some new services and the cash should have been set in the top left corner. The dashboard is consuming the portfolio service using the async RPC mechanism.