I am designing a CorDapp, which would require user input as well as API integration, and I am considering various approaches to expose flows and vault queries to the outside world.
Default option seems to be to use Corda RPC. Unless I missed something, there are only Java bindings for it, which is effectively restricting the clients to only be JVM-based. This is somewhat inconvenient, and ideally I would like something like OpenAPI to make it more open and implementation-agnostic.
Another option is to use some kind of Corda RPC to OpenAPI proxy. I know about Braid, and I'm sure there are others. Braid seems to support deployment as a Corda service packed together with the flows into the CorDapp itself, effectively making it running embedded into the Corda JVM.
Braid can be deployed as a standalone proxy too, which I suppose is option three.
Instinctively I find the embedded mode more attractive, as it reduces the number of moving parts, as opposed to a standalone mode. However, I am concerned that such model may be in fact become discouraged at some point, either because Corda developers consider it to be a misuse of services facility, or because some organisations will not be keen to deploy such code onto their nodes, especially when they may be running multiple CorDapps. I would imagine anything deployed as part of Corda JVM would at least require more scrutiny due to potential impact on other things running there, which in turn would reduce the agility.
I wonder what approach to integrate with a CorDapp is actually recommended?
Edit 1: I know it is technically possible to embed a webserver into the node and expose a REST API from there, at least in the current version of Corda (4.3 at the time of writing). The question is more about whether it is a good idea to do so, or not, and why.
Take a look at the question I had asked on Stackoverflow regarding front end for CordApp. This might be of some help.
Following is the link -
"Corda: Can we develop Dapps that will be run by IIS webserver to talk to Corda platform?"
You can use any front-end technology you want.
As of Corda 3, your backend must be JVM-based, for two reasons:
You need to load various flow, state and other class definitions onto
the classpath to pass as arguments to flows, retrieve objects from the
vault, etc.
You need to use the CordaRPCClient library to create an
RPC connection to the node
If you really need to write your back-end
in another language, there are a few workarounds:
Create a thin Java webserver that sits between your main webserver and
the node. The Java webserver translates HTTP requests from the main
webserver into RPC calls to the node, and RPC responses from the node
into HTTP responses to the main webserver
This is the approach taken
by libraries such as Braid
Use a library such as GraalVM to compile
non-JVM languages to JVM bytecode
An example of writing a JVM
webserver in Javascript using GraalVM is available here:
https://github.com/nitesh7sid/cordapp-example-nodejs-server-graalvm
Related
You could say I am a fan of the Realm Mobile Platform. I'm using it and it seems to be working well.
However I am confused with how to operate it going to production. It seems to be deployed only to one server, and even the professional and enterprise editions are working on my single server.
Assuming Realm have thought of this (as Enterprise edition supports 'enterprise scaling) - how does this work if all clients point to my owned server URL?
Another question is how to monitor the load on that server.
Thanks!
The Professional Edition and the Enterprise Edition emit statsd compatible metrics which allow you to track the usage and load on each node in a Realm Object Server cluster. These metrics are also used internally inside the cluster in order to display statistics about the health of the cluster.
We are obviously still adding metrics as we understand more about our customer's use-cases, and fine-tuning the ones that we have.
With regards to the way the clustering works, we are currently implementing this according to an iterative process, where we add more and more features, and more and more resilience to the system with every passing day.
Basically, we have a logical load balancer process, which receives the incoming client connections, and then dispatches that to a node inside the cluster. This logical load balancer can be HA'd and LB'd itself as well, just like you would any regular WS connection handler. Handling many connections these days is easy. It's handling the quadratic merge algorithms that is expensive on the Realm Object Server, which is why the clustering is required for deployments at scale.
I'm trying to implement a inbound resource adapter which will receive a data through HTTP protocol. I have two variants of implementations: to use Jetty as inner server and to use web container from WildFly. I know how to use Jetty, but think that Undertow using is the best. But how? WildFly does not see #WebServlet in RAR. How can I tell to WildFly to deploy a servlet which is located RAR?
When it comes to the point where the whole ecosystem is against me, I usually ask myself whether I'm sure the whole idea is right. Your idea does not seem to be right at all. Still, if you're sure, I'll explain the way of doing something that is close to what you want.
The idea of using servlet inside a resource adapter is a bit odd. Implementing an inbound HTTP adapter is odd either. In some logical sense, servlet container is an inbound HTTP resource adapter itself. It doesn't really utilize JCA container, but it's quite close to what an inbound resource adapter would stand for.
Another reason for not doing so is that resource adapters and application deployments have quite different life cycle. While WAR/EAR deployment represents an application which 'serves as it lives', the RAR semantic is quite different: instead of doing some business logic, resource adapter just provides interfaces for other deployments. You can bundle RAR into your EAR for sure, but if you're not targeting a monstrous monolith, you'll end-up deploying RAR as a separate artefact for your applications to use. Resource adapter should not contain any particular business logic. If you need it to do so, consider rethinking whether you need an application server at the first place: JCA container is quite poor comparing to EJB and Web ones, and if you don't need all the power, Java SE might come in handy.
Now, if you're still 100 % sure you need this, let's take a look at your options:
You may try to implement ServiceActivator -- a JBoss-specific start point for custom extensions. From within this activator you can access UndertowService and perform servlet container bootstrap manually. Here is an example of SA-powered artefact from Wildfly team. Since your question is quite unusual, I cannot confirm whether JCA deployment will support it, but it seems to.
If you cannot just force Wildfly's web container to process RAR deployment, you could fall back to a manual container instantiation. Undertow itself is just a module inside Wildfly so you can access it by specifying module dependency clause in your RAR's JAR manifest like so:
Dependencies: io.undertow
Undertow's classes will then be available to you upon deployment through your classloader and you'll be able to instantiate a new server with custom servlets inside.
Hi went through Enterprise Integration Patterns by Gregor Hohpe and Bobby Woolf.
http://www.eaipatterns.com/toc.html
I also went through Camel and Mule's compliance with these integration patterns -
http://www.mulesoft.org/documentation/display/current/Understanding+Enterprise+Integration+Patterns+Using+Mule
http://camel.apache.org/enterprise-integration-patterns.html
I see that both Mule and Camel allow applications to be deployed and accessed via webservices like SOAP or REST, SOAP being more RPC style. They allow massive integration support using opensource utilities like CXF and Jersey. In fact Mule also supports RMI endpoints - which will give remote method invokation capability as well which is a well-accepted form of Integration.
I understands ESBs are built around a Message Bus with additional support for other protocols however ESBs only comply to EIP and EIP is not just ESBs.
Question is why SOAP/REST or their transport protocol not considered as "Integration Styles" and which is Enterprise Integration so "Message Oriented"?
I am a novice compared to the great minds which designed these patterns but trying to understand the lopsided message-y nature of Integration patterns. I admit it isn't quite the QnA format of stack overflow but will request Mods to keep it alive for a while so that people can share their opinions.
As for SOAP, it would put it under the Integration Style "Remote Procedure Invocation", since it's pretty much what SOAP implements in reality (I won't consider the SOAP over JMS hybrids here with a potential to mix RPC with Messaging..).
REST is, interface wise, very different from SOAP in that it's resource driven instead of service driven. I would non the less group it under the "RPC" style since it's just another format of syncrhonous RPC calls.
I would, however, not put too much effort in theory of what EIP integration style a specific message pattern implements.
Look at a specific scenario at hands instead and use the EIP to model your specific integration.
I've seen integrations of file transfers that in realtiy implemented RPC patterns or SOAP services that in reality implemented messaging (although I don't really recommend do this).
A concrete example: consider the usage of a dedicated file upload service, which happends to be built using SOAP technolgy, which uploads a CSV file to a file area on a server, from where it's picked up by some other system. I would call this file based integration on a high level.
Another example is that Messaging systems sometimes are implemented using a shared database. Still the integration style using them is messaging, not "Shared Database".
Think about how your integration should work on a high level, then apply the various protocols to do the grunt work.
Suppose I have two or more different server applications developed in Clojure using ZeroMQ and BSON as protocols. How can I deploy them using a single JVM instance while also sharing common dependencies?
It seems a waste of memory to use a JVM instance for each standalone application. I plan to develop several Clojure applications in the future and VPS memory is not cheap.
Although not explicitly said, applications running in an application server (Jetty, Glassfish) seem to share the same JVM while isolating their state. However, they require a container and neither Servlets or Enterprise JavaBeans have an implementation that I could easily adapt to my custom protocol.
I've been thinking about using Servlets and implementing a dummy service() method though I don't like the idea of having a pointless HTTP server overhead. As for the EJB container, I cannot even figure out its implementation.
It would be nice to have a container requiring only init() and destroy() methods but I can't find an application server providing it.
Maybe there is a way around or I don't even need an application server. Could somebody point me in the right direction?
It sounds like you would be okay using an EJB container, but only if it were easier or simpler to work with. Have you looked at Immutant? It's basically a wrapper around JBossAS for Clojure, written by guys at Red Hat (who also own JBossAS).
In addition to being an application server, those guys have wrapped JMS and other Java-EE features around Clojure, such that sending messages between apps appears pretty simple:
Also, they have Daemons and Jobs, which may provide something similar to what you were describing as simple services with init() and destroy().
That being said, I haven't used it, so I'm can't vouch for it's awesomenss/awfulness.
So you have two applications that both share the same dependencies and both want to respond to and/or generate events on a message bus.
If I understand what you're saying, this should be as simple as starting the JVM with access to all code in the classpath and initializing your message bus and your code from a main method.
If you wanted to use a container, you could create some dummy message driven beans that sat between your clojure code and the message bus assuming there is a JMS adapter for your message bus. Using netbeans/glassfish, this may not be that bad. You might gain some in terms of monitoring, but I'm not sure what else you would gain.
I kept searching and found out that some application servers implementing the OSGi service platform have simpler lightweight containers than those offered by Java EE.
Apache Karaf for instance can load POJO applications directly from JAR files.
I am not sure what DDs are but any JAR is a valid bundle. Since clojure is not type safe you will need to bridge the clojure world and OSGi/Java world but the OSGi API is a wet dream for such bridges.
Not that in OSGi bundle do not automatically provide their content, in OSGi a bundle is by default private. However, the API allows you to punch holes where ever you want.
my plan is to develop or use a Java-based integration framework (ESB, SOA whatever) that deals with services, with the following constraints:
a Service can be deployed on multiple machines but doesn't have to be present on every one of them
a Service can be deployed and re-deployed (with a newer version) separately
a Service is connected to other services either by:
in-memory connections
(async / sync) remoting to other machines
the routing logic of the Service connections should be configurable on the fly, without re-deploying or restarting anything
I know that OpenESB is close to these requirements, however it requires redeployment of the service to change the routing (suppose the connections are HTTP BC based), but I'm unfamiliar in this regard with MuleESB, WSO2, JBossESB, whatever open source ESB... Is there any good solution for this (e.g. configurable in-memory and/or remoting routing)? I don't really care about clustering as I plan to use the servers separately, and the designated (if required) JMS solution would be HornetQ if that matters.
You mention several different concepts, but a combination of an ESB pattern, Apache Load Balancer and Maven should get you close. Do not get to hung up on the product, settle on a paradigm/pattern and the decision of the product will be easy, it either does things the way you like or does not.
Here is the pattern I use.
SOA Design Patterns
This may also interest you SOA for executives
Cheers
After a long discussions about the pros and cons, we are going to have a HornetQ-based (JMS MQ) solution, where we create message routing rules and sometimes processing codes that handle the different kind of routing. HornetQ is able to handle the in-jvm requirement too, but that part will be covered under the hood.