We've developed a significant project in DropWizard, but the nature of the project has shifted, and we're moving away from having actual HTTP endpoints and toward RabbitMQ. However, DropWizard has a lot of cool features we'd like to keep using, and besides the pain of replication, it would take a lot of worker hours to stop organizing things as (e.g.) DropWizard services.
With all that said: is it possible to run a DropWizard application without any open ports?
Yes you very well can, see here & here.
DropWizard has a lot of cool features we'd like to keep
using
Which feature are you interested in?
Since Dropwizard is primarily built to serve HTTP traffic, it has Jetty & Jersey which will be initialised on your app startup, it doesn't make sense for your app to have these if you never plan to build an some sort of an API inside your app (say for custom-monitoring, health-checks etc.,).
I would like to take a doubt about the container to run a "Spring Application", in my opinion one of many features who Spring Framework offer is a possibility to create application without container EE. Is right use this type of container ("WildFly", "GlassFish") with a spring project ? In my option is wrong but i'm open to listening more people.
i saw a article where the author are showing the features of Spring 4 with the WildFly, but i didn't agree, so i would like to take more opinions about this topic here.
Considering Spring Web and Web MVC you will typically use a lightweight container like Tomcat, Jetty or any other servlet container - maybe embedded like Spring Boot does.
Spring Web is designed to work without a full JEE container but will also work deployed inside one.
With Spring without JEE you have much more control about the features you use. A full appserver has a bundled feature list, you get all or none. Spring offers you to pick what you need resulting in a more slim application.
Well, first of all it is a little tricky to say that "something" is wrong or right in software development, mainly in this type of subjective question. As always, that really depends on what you need and on the EE Container that that you are using.
Let's get Widlfly as example. Since JBoss 7 (and now Wildfly) I do not think we can say that JBoss is a "heavy" Server, as it starts in just a few seconds, much faster than in the earlier versions. While it is true that Wildfly comes with a lot of services that you may not use, it is not correct to say that you get "all or none", for at least 2 reasons:
You can disable the services you do not need.
Wildfly works with the concept of lazy-loading for its services, which means that it will only load the services that are required to run a given application.
Having said that, we can not forget that Spring also uses some EE services, if you want to. So, if you need to use Spring with JMS, for example, you still need a JMS container. In this case, you can use an EE Server without needing to install additional services or you can start a JMS container in your Tomcat.
Besides the EE features, there is also the question of features related to the server, such as configurability/manageability (Web interface, CLI), HA, scalability... that really varies from server to server and I think Jboss 7/Widfly does a good work on these points.
Ok, I know this is a vague question, and I expect a vague/basic answer.
I am well versed with PHP driven MVC frameworks and how the process of serving pages works. I'm very interested in learning Java, and I figure the only way to learn it is to do it. However, after reading page after page after page, it gets more confusing as I read.
I'm running into GWT (front end), Hibernate (ORM connection?), Spring Architecture, Spring Roo (what is this?), JBoss (servelet), JPA (ORM), POJO (a style of using regular java objects with orm?), Maven?
My basic question is how do all of these fit together? I like the idea of using a framework, because it's worked well in the past with PHP. How do I use this functionality with java? Suppose I wanted to build a web application with a relational data store. How does java authenticate, initate a session, and serve pages with dynamic content? What is the process?
When responding, please don't say "stick with what you know," (as I've seen on other pages) because I'm very interested about java and I'm trying to learn.
I totally hear you - too many acronymns have propped up as Java EE has evolved.
I will try to put an explanation
Java is the language
Java EE (Java Enterprise Edition) is the general term used to encapsulate all Java technologies that help create an enterprise/web application with Java
So a typical web application with Java looks like follows:
Front End
Use JSP or JSF for server side processing and rendering (JSP and JSF
offer ability to define your UI using HTML and server side tags that
bind easily with your Java Beans) However they do tend to mix UI with
backend if not implemented correctly
you can also use plain HTML and any client side toolkits for rendering (such as jquery, dojo, extjs or flex) and fetch your data
from the Java EE server.
you can even mix the two (use a client side framework in a JSP to achieve best of both) or use a toolkit like GWT that offers client side richness with javascript with Java APIs and ease of accessing your java beans
Middle tier
Java Servlets offer the base for all server side processing with Java EE (Servlets offer session persistence, HTTP request processing, response processing) and typically offload the business processing to a model bean - which could be a POJO or spring bean.
Servlets are Java programs you write and are executed in what is called a Java EE container. Popular containers are tomcat, IBM websphere, BEA Weblogic
To help implement a good MVC architecture, there are several frameworks and tools provided on top of Servlets:
Struts2 and Spring MVC are examples of such frameworks
To make it easy to implement web services, Restlet/Jersey help with REST based web services, JAX-WS/APache Axis help with SOAP based web services
Integration with backend database/persistent store
You could use JDBC in your POJO or other model bean to access the DB using Java.
Or alternately use one of the frameworks such as Hibernate to make it easy to interface with the DB backend
Sun's petstore application is a good place to start to learn how the pieces fit together
http://www.oracle.com/technetwork/java/javasebusiness/downloads/java-archive-downloads-eedocs-419425.html#7522-petstore-1.1.2-oth-JPR
Build and Deployment
Ant and Maven are tools used to build your app and manage dependencies
the application gets packaged as a WAR or EAR file and can be dropped into any Java EE container to deploy it. Once it is deployed, it can be accessed using a URL
Tools like Eclipse, Netbeans, Oracle JDeveloper offer integrated IDEs to help with local deployment and testing
The good part with Java EE is that you can pick and choose the components you want to use to build your webapp.
The problem Java has is that it's fairly old and there are TONS of frameworks and packages that do similar things as other packages. At the very core, however, is the Servlet, that specifies how Java behaves as a server over the HTTP protocol.
With that basic building block, there are lots of web frameworks like Struts, and Spring MVC that build up layers of functionality by using lots of good OO development patterns, like Fiters, Delegates, Factories, MVC, etc., to allow the developer to put together an application that takes web requests as input and returns a web response as output.
Those frameworks often build on other frameworks or packages to give application developers more capabilities at different layers of the application. This includes things like ORMs (like Hibernate) to talk to relational databases, or view compositing frameworks like Tiles or Velocity to help put together an HTML page as part of the response.
There are lots of other acronyms and tools and layers that get built up around web frameworks, but essentially they are all just programming tools that have useful functionality pre-built and just need to be used.
If you are looking for a more packaged web application development framework that is more cohesive and doesn't make you feel quite as lost, you may want to take a look at Grails. It is in Groovy, but it is very close to Java in terms of the language and actually builds on top of lots of the other tools you have heard of.
Grails itself builds on the Spring and Spring MVC frameworks, as well as Hibernate, so it's using the same technologies as other more pure Java frameworks, but it abstracts the ugly details away so you don't have to worry about them unless you want to. You can then bundle in additional functionality, like authentication / security, through plugins. If you are well versed in PHP-based MVC frameworks and how they work from an architecture standpoint, you will feel right at home in a similar MVC environment like Grails or Spring MVC. The Grails User Guide is a great place to start, and the rest of the documentation is good too.
If you are new to the Java language, I would strongly suggest doing a few small applications (not web apps, just simple ones) to learn the language and get familiar with how things work. Java is very different from PHP, since PHP bundles in a lot of the base functionality into the language whereas Java has a fairly sparse language with much of the commonly used functionality coming from libraries.
Once you have a good grasp of the Java language, I would jump right to the Grails framework and I would skip all of the nitty-gritty details of servlets and ORMs and Hibernate, etc. at first because you don't need to know it all and there is so much there that it can get in the way of actually understanding things.
Then, once as you start to build out an application with Grails, you will gradually get a deeper understanding of the technology Grails is built on in order to do more complex and powerful things. Slowly, you will work your way into Spring and Hibernate and build up an understanding of how things are put together under the covers, but you can be doing real things faster since you don't have to know all of that from the beginning and can quickly make web applications in Grails the just work, especially with an understanding of the MVC architecture pattern with respect to an application responding to a web request.
Wow, not only is this an open ended question, but it could have pages and pages of answers. I worked in php ~ 7 years ago without a framework so I'll try to point you in some starting directions and compare my experience (which is outdated and sans framework!)
You need an application server just like your Apache server for your Java web app, such as Tomcat, Jboss or Glassfish. These servers handle serving dynamic content.
On top of the server you have your web frameworks which you've mentioned GWT, Spring, and Spring Roo. Spring Roo is like Rails, but in Java. GWT goes all out and and will write your html/javascript code based on your Java code.
In Spring You can define objects to be used in your forms and then when they are submitted the entire object is passed back so there is less work. I remember the days of getting a lot of $_POST[] stuff and I'm thankful not to have to do that when using spring. There is Spring Security that you can use for auth.
The web frameworks are configured to connect to the database and then there is the database abstraction ORM, Hibernate. In PHP I used EZSQL for abstraction which didn't contain nearly the amount of features Hibernate does. Hibernate has a steep learning curve, but is worth learning.
For dynamic GUI's you'll probably want to research JSP, but may be interested in learning JSF.
If I were you, I'd pick an application server, maybe tomcat, then a web framework to play around with, personally I'd go with Spring. The framework will probably have dynamic GUI examples so you'll pick up jsp/jsf. Then possibly add the ORM and a build tool to build externally from your IDE, such as Maven, Ant, or Gradle.
There are some very mature java libraries that each target a very small need in a web application. This means that many tutorials on the subject will have to pick and choose the libraries for each need. For someone just starting out from your position, this probably sucks.
Naively, then, I searched for "java full stack framework" and found: Full stack framework for Java
The benefit of a full stack framework is that you don't have to choose each component. The framework has strong (perhaps rigid) opinions on how ORM is done, how templating is done, how mapping URLs to functions or actions is done, etc.
As for your list of technologies and acronyms:
GWT - a framework from google that focuses on the front end. Poorly stated, write your front end functionality in Java and have it magically transform into javascript.
Hibernate (ORM connection?) - yep, store and load objects in your app.
Spring Architecture - Spring is pretty close to a full-stack framework, but it doesn't have as many rigid opinions on things. You can swap out templating engines, swap out ORM, etc. Not a bad framework, though. You might want to simply follow a tutorial on Spring (see below on Roo), and use the components suggested by the tutorial. Just know that you might find something else later that fills a particular niche.
Spring Roo (what is this?) - Spring Roo takes Spring and becomes opinionated (use what we say). This allows for less code on your part because it provides the code that integrates the various components. It still allows quite a bit of flexibility when you want to change something. Bonus, it comes with a nice tutorial.
JBoss (servelet) - Usually I think of JBoss as an application container. Since the Java EE spec is a bit more complicated than simple CGI--there's a lot of things that need to be set up by the web server (loading classes, loading configuration files, connecting crap together)--JBoss does that stuff. Alternatives are Tomcat or Jetty.
JPA (ORM) - Yeah, it's a common set of interfaces that the various serialization providers might implement. It might be a database, it might be something else. But the idea is that your code for storing and retrieving objects would look the same.
POJO (a style of using regular java objects with orm?) - In context, probably. "Plain Old Java Objects" are nice for any library. Sometimes a framework might require that you inherit your classes from some special class, like Model or Controller to work properly (also, HTTPServlet). This isn't good, because it restricts your own class hierarchy design and makes your own code less flexible. Consequently, things that work with POJOs are considered better.
Maven - Maven is a tool that helps manage dependencies. Without it, java has its own form of DLL hell. Library A depends on version 1.1 of Library B, but Library C depends on version 1.5 of Library B. Ohhh crap, time to read through a tutorial on classloaders. Don't worry too much, though, any tutorial on java web apps is likely to tell you exactly what you need to download and use.
The first thing I would suggest you to start with, given a knowledge of http protocol, is the JSP technology. Although you would probably use some framework like JSF2 for instance, it is important to start with JSP in order to well understand the technology and how to use it to deal with request/responses (that's my humble opinion of course).
Once you are familiar with JSP and, let's say, JSF 2.0 (you can find loads of documents on that topic) the next step is to try to connect with a data source. In Java EE technology there is a specification called JPA (Java Persistence API). JPA is just a specification for ORM (which is, roughly speaking, mapping an object java model with a set of DB tables)
Once you have your web application working with some basic pages and some operations on a DB you could enforce the security of your app introducing some security mechanisms.
this is a very good reference and start point for all of these topics and much more. It's a long path and it will take you some time. But, believe me, it's worth it!
Good luck!
I suggest you google those keywords and look for some books and tutorials.
Maven
is a tool for managing your Java projects and artifacts (JARs, WARs, etc.). I'd start learning Maven first, so that you have a foundation to create your Java projects on. It also handles your dependency management: you just specify what JARs you need in your application and Maven will download them for you.
JPA (Java Persistence API) handles the Object-Relational-Mapping of your entities. You can write POJOs (plain old Java objects) and map them to your database tables.
Hibernate is a JPA provider (i.e. implementation of JPA). Usually you don't have to deal with Hibernate that much, most of the time you can use JPA directly. You just configure the JPA provider in the persistence.xml config file.
CDI (Context and Dependency Injection) see description. CDI "wires" the components of your application together.
Springframework started as a framework to offer Dependency Injection capabilities, but today it's much more than that. The WebMVC module of spring might be interesting to you. You can write Controllers and Views (using JSP for example).
Servlet API A servlet acts like a little server, handling a HTTP request and generating the response. You can write your own servlets or use a web framework to do it's job, for example Spring's DispatcherServlet or Java Server Faces, or whatever framework.
JSP is a technology to write templates for your HTML files. JSP files are being compiled into Java classes and can contain HTML code, JSP-specific XML code and Java code.
Example:
<ul>
<c:forEach items="${countries}" var="country">
<li>${country}</li>
</c:forEach>
</ul>
renders a list of countries, where ${countries} might be a collection of country objects (or strings in this case).
JSF (Java Server Faces) is another framework for building web applications, utilizing JSP and/or XHTML for defining the views and backing beans for the backend part. I would start learning with JSP instead of JSF, it's easier to learn.
Most of the frameworks are part of the JavaEE standards portfolio. For stuff like CDI to work you need either an application server (like JBoss AS) or at least a server with a servlet container (like Apache Tomcat or Jetty) in combination with Spring.
Spring and Hibernate are not standard, but they implement many of the standard APIs nowadays.
**EDIT: ** you might also want to learn about Annotations in Java code. They are around since Java 5 and are widely used as an alternative to XML based configuration.
So my suggestion is that you start learning Maven (not necessary tho, you can also manage your project manually), then Spring and JSP to be able to create a simple web application and then JPA/Hibernate to make your data persistent.
In my opinion learning Spring is much easier than learning the whole JavaEE APIs, since Spring is quite good documented.
One of the nice things about GWT is that you'll right your client code in Java, with all of its benefits and if you have server code, that could also be in Java as well, and you could share some of the source code, even if the front-end ends up running as JavaScript.
TO build a basic Java web application, go through this tutorial as it will explain the core foundational technologies with the standard Java EE platform and how to develop something real with them.
http://netbeans.org/kb/docs/javaee/ecommerce/intro.html
It will demonstrate the standard Java web technologies such as EJBs, Servlets, JSP, JPA, and how to use Netbeans for your IDE.
Most beginner's are very overwhelmed by the thousands of different technologies and platforms out there with the Java EE framework. Java caters to a very 'open source' type of community and that means that you have ALOT of different choices and road maps on how you can build applications. This is very different from say the .NET world where everything is pretty straightforward and there's a very clean cookie cutter path.
Once you have learned these foundational basics by going through the tutorial, you will have a grasp on what the Java EE framework. Once you understand these basics, you can then start to learn about Maven or Spring and how those type of technologies can help you build better applications and you can make better and more educated decisions.
GWT - Web interface tools. Some competing technologies: Spring, JSF, Wicket
Hibernate - ORM mapping for databases. Competing technology: JPA
Spring Architecture - Web Framework. Competing technology: JSF, Wicket, GWT
Spring Roo - An MVC style flavor of Spring.
JBoss - Application hosting. Competing technologies: Glassfish, Tomcat
JPA - ORM mapping for databases. Competing technology: Hibernate
POJO - Plain old java object. Just a simple object.
Maven - Maven is a way to manage libraries or dependencies that your project uses. There's a central server that hosts many of these libraries and if you ever need to import a new one to use in your project, it's as simple as searching through the server and then copy and paste the configuration settings that they provide you into an XML document called the POM file or pom.xml
Vijay's answer above is pretty much spot on. I'll elaborate on a few points.
Most of the "fameworks" that you mention, spring, roo (which is just a way to work with spring), gwt, struts, etc. all work on top of "Java EE". Java EE is Sun (now oracle's) term for the "standard" way to work with web applications. Java EE also includes a lot of more enterprise stuff like EJBs, JMS, JMX which you won't really need to concern yourself with unless you're doing very high end stuff.
JSP is the part that will be most familiar to you coming from PHP, it's a way of embedding code inside of an HTML page.
Servlets are the middle tier, that's where database connections are created and application logic happens. As it turns out, JSPs are converted into Servlets at compile time.
All Java EE stuff runs inside of a "servlet container" or an "application server". That's the big difference between java and php. Your choices here are usually Tomcat, JBoss or Jetty.
Maven is a build system that helps you to manage 3rd party jar files (libraries) and compiles and runs your test codes. It has plugins to deploy your code to tomcat/jboss/jetty.
POJO stands for "Plain old java object". Most modern frameworks try to shield you from the complexities of what happens under the hood and let you work with "POJOS". This comes into play when working with something like spring or hibernate. You may also see the term "java bean" tossed around, that's a standard way of defining "pojos" that just sets up a convention about how to name getter/setter methods and constructors.
I would recommend getting a book on getting started with JSPs/Servlets and starting there.
I'm developing a java application or service for execute remote commands or another applications and receive the results of these commands. And I think about to project this application to be possible his use with a swing interface or a web interface.
I have to take care with the parameters to pass for my businnes classes and how I will deal with the results. I need to use a architecture and project that let me able to use my classes with a desktop application or web application too.
I believe this is related with API and service design. Some popular applications have a web interface or dashboard for control services, and the services are manageable by agents installed for execute some demons, services or applications. To do start or stop commands for database systems, directory services an other tasks
There are some guides to how develop applications and services in java that can I use with web and desktop environments?
I felling a bite confusing about this, because in my mind if I choose to develop this with a swing approach all the thinks turn clear for me. But when I imagining the same project using the web perspective I lose my directives.
Sorry and Ihope that someone could undertand me. :-P
Consider spring and MVC architecture. Neither of them is constrained to Web development only, however they are extensively used as such.
You might look into Naked Objects ,where you develop a domain object model and gets the UI more or less for free (You can get a desktop GUI, and various forms of web UIs). This is probably not a feasible approach if you're developing a public facing application, but more suited towards applications developed for expert users.
I have been in a similar situation recently while I started working on a simple CMS. I wanted my cms engine to be free of what UI/client is used to interact with it and finally I settled for a Web Service oriented approach. As a student of RESTful WS/ROA I usually like to take that approach.
If I understand your problem correctly, I would design it to be, each external program, service, web service I want to provide remote access to would be a 'Application' to my web service, where 'Application' would be a 'Resource'. Performing actions on the 'Application' resource would mean executing GET requests with different query parameters. How the 'Application' infers would depend on the 'Application' resource.
A similar approach I took in the CMS engine is for generating representations for a content. I support Ruby (JRuby), Groovy, JavaScript (Rhino) and Velocity template for generating representation. User creates the template script as a resource and refers then in the content type definition. Clients are provided URI's to the representation from the content generic media formats (Atom XML, JSON) and upon fetching them receives the output generated by the script. I am tempted to take a similar approach for your problem. It would not only separated the UI from the business objects, but also provide flexibility to add new backend services in the long run.
As tools for RESTful WS over Java I would recommend, Jersey, Abdera, Jackson. As an example for how use them together you can have a look at the CMS project I was referring to.
Hi i would suggest you to build your system with a modular approach such that
you have all your business logic is exposed as a service which can be accessed by REST,
in addition create you can have web application layer and a desktop layer.
schemantically it will look like be at a higher level
weblayer/desktop---------{REST interface} ------- {business logic}-----EIS
and for modularisation you can consider OSGI
hope this helps
Hi
I want to design and develop a big enterprise application using just
GWT in client side.
I want to break this enterprise application into parts and I call each
of them a module (or bundle or portlet or whatever!).
These modules might have relation with each other and might call some services that
exists in other modules (in both client and server side).
The problem is, These modules must be Designed , Developed, Compiled
and Deployed Independently and Dynamically and they will be placed and
shown together in one context on the client and the dependencies
between modules should be manageable (in both client and server side).
What can I do? What kind of technologies I can use to build an enterprise application like this?
When you develop an application that is not divided into parts (In the way that i mentioned) you can easily deploy your application after building your project, but when you change just one form in your application you have to build the entire application again, and deploy the entire application.
In this application I cannot stop the server to deploy the application again, I want to change and deploy that part of application that is needed to be changed not the entire application!!!
Of course I have searched about the way that I can solve my problem!!!
I have found that I can use OSGI on server side because it provides modularity at software construction level and helps me to manage life cycle of modules and many other benefits that you know!
And I have found that I can use Gadgets on client side.
What do you think? Are they good choices?
If they are good choices, how can I start? I know that we have different kinds of implementations of OSGi, like Apache Felix, Eclipse Equinox and Knopflerfish. Which one is good for this choice?
How GWT and OSGi can be integrated? How can they interact with each other?
Unfortunately what you want to do is not fully possible with GWT.
OSGi is a modularity solution for Java, or more accurately the JVM. A GWT client application does not run on the JVM, it runs on the browser in a JavaScript environment. Therefore OSGi cannot be used to create runtime-assembled modular GWT applications.
A GWT application can be modular at the source level, but the modules must be assembled into an application at build time. The resulting runtime is monolithic.
However, it's perfectly possible to use OSGi to host the GWT servlets, and you can use the full power of OSGi runtime modularity on the server side.
As an alternative you may want to look at Vaadin. This is a web framework that uses GWT to provide widgets, but the logic of the application runs on the server. As a result, it does support full runtime modularity through OSGi bundles. There is a cost with this approach though: your web application is quite chatty, with lots more communication going between the browser and the server than in GWT or in a traditional web application. It's possible that this approach will not scale to very large numbers of users.
As for whether to use Equinox, Felix or Knopflerfish... it really doesn't matter. Stick to the specification, and you can easily switch between implementations.
I did just this two years ago: OSGi and GWT for no downtime deployments of project modules.
Verdict: Don't do it unless you really must.
In short, OSGi is a beast and retrofitting an existing application for it is far from trivial. You're no longer making .war files (.ear now) and can't use the standard jars and Maven repositories you used before. Now everything needs to be a bundle. Trouble is, a lot of stuff (GWT, Spring, tons of libs) are not bundles! And you'll need to find them in an enterprise bundle repository or, even more fun, start rebundling 3rd party sources them yourself. Better yet, telling the other devs to rewrite everything that uses their favorite lib because bundling it would be too complex.
The GWT part didn't take that much work. The way contexts for modules were handled in gwt-servlet had to be modified so each module could find it's context on the server. We also had to make a way for most of the GWT services to register/unregister on load and a discovery service so they could know who else was out there.
Now the other pain: project explosion.
Let's say you had 20 modules you wanted to deploy independently. Well, to start with they're probably more coupled than you'd like, so better spent a few weeks breaking them into independent Maven projects and pushing common parts to a lib project. But now, you've got tons of dependencies to keep track of. When someone tweaks your lib project, do you need up upgrade every project or just 7 of them? In the classic stop the world deployment, you only had one version of all your code. Now, you need to decide if that forgot password form being upgrades will require you to also upgrade your index page module. You'll have a ton of version numbers to make up and keep track of. In our case, we quickly had 55 Maven projects building all the time in our CI server. This meant some checkins could trigger 55 builds. Eek.
Finally, JSON interfaces.
We used GWT RPC. It's magical. Write an interface and everything just works. It's also serialized and gzipped over the wire too. Awesome. But, the serialization policies depend on object and string lookup tables that are built at compile time per module. So, project A cannot RPC to project B. Boo. We chose to use JSON due to the graceful degradation, that is not failing when new unrecognized properties were present on objects. This means you'll again need a way to keep all the backend service calls coherent in the versions of the JSON they are expecting and can handle. Better simulate that live upgrade beforehand too.
So, final word: possible, but why? Do you really need OSGi to hot deploy modules because you're running a 1000% uptime business critical application? Or does your boss/architect just refuse to accept that 99.999% is good enough? You probably don't need that uptime and can achieve nearly 100% uptime with a good proxy to let you take instances in/out of the balancer pool. Also, don't forget that even if you can upgrade your projects live on the fly, I hope you've got a way to upgrade your database on the fly without dropping a single transaction.
I think you are setting yourself for more headaches than it is worth.
I would go with deploying the whole thing at a pop. If not you will end up with mismatched pieces of the application that are out of sync with each other. GWT has both Client and Server components and they need to be deployed together. If you have a zero downtime policy then you probably have load balancing in place.
I would use the load balancing software to deploy the new version of the app. Turn off one side (by diverting all traffic to the other side) deploy to it, do a quick smoke test, switch all traffic to the new side and repeat with the old side.