Recently a friend of mine asked me about N-Tier architectures and I was able to explain to him about 1, 2 and 3 tier architectures with examples. But I was stuck when I wanted to give examples for more than 3 tiers. I googled and binged for help, but could not find any decent examples.
The fact that it is named N-tier makes me think that 'N' can be any number starting from 1. But I couldn't find any examples for 4 or 5 tier.
Can somebody share some examples of N-tier architectures that involves more than 3 tiers?
Fundamental Services : e.g. Database, Directory Services, File & Print Services, Hardware abstraction. This tier is increasingly called the platform.
Business Domain Tier : An Application Server such JavaEE including EJB, DCOM or CORBA Service Objects. Provide business functionality, increasing using SOA and Micro-services.
Presentation Tier : e.g. Java Servlets/JSP, ASP, PHP. This tier will increasingly include WebServices as proxies and adaptors for business tier services.
Client Tier : Thin clients like HTML Pages on Browsers and Rich Clients like Java WebStart & Flash.
In Java EE it is common to divide the Business Domain tier into Data-Access (Entity Beans) & Business Services (Session Beans).
In an Enterprise SOA (Service Oriented Architecture) the ESB (Enterprise Service Bus) would typically exist as an additional tier between tiers 1 & 2. It may be part of the platform provision.
In Mashups you could have an aggregation tier between tier 3 & 4.
The move to being called N-Tier is a reflection of the move to increasingly componentised architectures from the older client-server to first 3-Tier then 4-Tier. The defining characteristic of a tier is a clearly defined interface with a separation of concerns.
Five minutes ago I've read an article of this
https://www.nginx.com/blog/time-to-move-to-a-four-tier-application-architecture
Client is where you read it
Api or your application back-end is where you assemble it ..
Data aggregation.. Either goes through the jsons/xmls from outsourced things or queries on your database and lastly service tier is where you actually do the query on database or run function on big data or read GPS locations and maps from google ... That is how I see it in this case. It simply divided the data layer from three tier.
But this N-tier model is totally abstract so you can tear your infrastructure until you have some logically atomic parts only. Still dividing the previous structure.
I'm leaning towards less abstract and more practical explanation that answers the question: "How and why do I want to split my system into tiers and where do I place them on the servers?"
Essentially, when you create a simple website that uses a database, you already have 3-tiers "out of the box":
data tier - the database. But if you are using a short-lived memory cache or file system then we might argue if that can be considered a "tier" or not.
application tier - the code that executes on your server(s).
presentation (or client) tier - the code that executes on the client's machine and presents the results to the client
Now, how do we get the 4th tier?
Most probably, there is no need to split the client tier. It's on the client's device and we want to keep it as simple and efficient as possible.
Could we split the data tier? I have seen some systems with APIs around databases, Azure blobs, file systems etc. to create some subsystem that could be considered a tier. But is that still the same data tier (a.k.a fundamental services tier) or can we consider it a separate entity? And if we separate it out, will it be on the same physical (or virtual) server as our database, so we can protect the data from direct access?
However, in most cases, it's the application layer that gets split.
One part is still named application tier. It becomes an internal API web application and lives in secured zone where it can access the database. Nobody can access the database directly, but only through this application layer.
The other part becomes a consumer of the application tier APIs through some kind of a connection (HTTP client etc.). The consumer might be called presentation tier (confusing - wasn't it the same as client tier?), even if it itself has only JSON APIs and no any user-friendly formats.
But then the question arises: in which cases we, developers, might want to complicate our lives and split our web application into presentation tier and application tier, instead of keeping them as layers inside the same web application?
At serious workloads, a separate application tier might be good for scalability or it might be a requirement of security to deny database connectivity to the web server that is exposed to users (even the intranet ones).
I have seen some ambitious projects going for 4-tier from the start and then cursing themselves for overengineering things. You have to keep track of those internal connections, security, authentication tokens, keeping sockets under control (not opening a new HTTP connection on every request), avoiding accidental sharing of data of multiple parallel requests through carelessly created global HTTP client instance etc.
That would depend on what you want to call a Tier. Each vertical of the Presentation layer could be called a tier.
Mobile app or webpage frontend (one page Javascript and the like)
The caching or CDN (Content Delivery Network) as another layer.
Frontend or API tier
The business layer, could also be split if the service requires multiple microservices. For instance
a Business process tier
an Administration tier.
Then the data Layer split into:
Database
Data Lake
Reporting
Enterprise Service Bus
Third party access data (where your app is connecting to other APIs)
For more see Cloud Application Architecture
A four tier architecture consists of the following
a. client tier -- node.js angularJs, etc basically independent of server side and UI team work on the client artifact independently
b. Aggregation tier --- content delivery networks (akamai)
c. api tier -- gateway for all the server side calls and can have its own caching
d. services tier -- includes internal or external services...
An easy example of 4 tier architecture is RMI JDBC Servlet. This involves
The client tier
The application server for theservlet
Rmi server for server program
Jdbc server for database
Related
I have 2 years in the IT industry,i love to read a lot ,but when i go deep in some subjects i see a lot of contradiction in somes articles,forum or terms that are used interchangeable.
I understand the difference between Soap and Rest.
When we want to communicate between backends, we can use either of these 2 approaches, each with its advantages and disadvantages.
Situation :
If i have an application, which can be monolithic or not, where I have a backend and I will only have a front end that consumes it. Usually we create a Rest Api so that our front end can consume it. But we will never think about exposing our backend with Soap.(Lot of reasons)
Questions:
1 -Is it okay if I say that Rest , in addition to allowing us to exchange information between application and application (backend to backend ), is it also useful when exposing services for our front end? And SOAP is only useful for Server - Server communication?
2 -And finally, if I expose a backend only for a front end, it is ok to say that we expose a web service or conceptually we say that it is a backend for frontend ?
Question 1: No the First question is wrong Assumption. We can say that in SOAP, XML is the only means of communication, while in Rest, the accepted means is JSON, while there are other formats like XML, JSON, PDF, HTML etc. and Ofcourse, XML can be converted back from server into UI Language and XML Request deciphered at Server for a Response. So, its not Ok to say that SOAP is only for Server - Server Communication.
2. No, when you have typically exposed backend only for consumption by a Front end, you can typically say that it is a backend for numerous front end client requests. But IMO, Backend for a front end is a monolithic webapplication, both bundled in WAR. so in that sense, any UI Request can request response from the Back end web service. Hope i am able to clear your understanding about web services.
I see that in your question there are actually 4 embedded independent topics. And probably because they are always used in conjunction it is sometimes tough to understand.
I will give a short answer first:
REST and SOAP both can be used for Client-Server and Server-Server integrations. But the choice will be dependent on the questions like where you want server-side UI technology/client-side UI technology or is it a single page application/portal technology, etc.
If you expose a single-backend for a single-frontend it's technically a BFF although the term BFF is used only in the case where you have separate-backends for each type of frontend application. e.g. one for mobile, one for web, one for IoT devices, etc.
The long answer is to clarify the 4 principles. Let me give a try at this by separating the topics into the below four headings:
1. Backend(Business Layer) vs Backend for frontend(BFF)
In classical 3-tier architecture (UI-Business Layer-Database) world, the middle-layer that consists of the business and integration logic is mostly referred to as backend/business layer.
This layer can be separated from the UI/Frontend using multiple different options like APIs(REST/SOAP), RPC, Servlet Technology, etc. The limitation with this 3-tier architecture is that, it is still tightly coupled to the type of users and use-cases are limited to web/browser based. It is not a good choice when you want to reuse the business-layer for both web and mobile as the mobile applications are required to be light-weight by principle.
That's where we lean on to multi-tier architecture with Backend For Frontend(BFF) as a savior. It's just a methodology to segregate the business-layers based on consumers.
2. Monolith vs SOA vs Microservices(Optimized SOA)
In a monolith world all the code components mostly UI and Business Layer sits in a tightly coupled fashion. The simplest example would be a Java Servlet Pages(JSP) application with Java as Business Layer. These are typically server-side UI technologies.
In Service Oriented Architecture(SOA), the usecases revolve around leveraging reusable business layer functions aka services. Here one would have to deal with UI-Server, Inter-Service and Server-Server integration scenarios. It's heavily service dependent, meaning it's like a spider-web of dependent applications.
The Microservices is an extension of SOA, but the approach is to keep a resource in focus instead of services to reduce the spider-web dependencies. Hence, self-sufficient and standalone service-clusters are the base of micro-services architecture.
3. SOAP vs REST Webservices
SOAP stands for Simple Object Access Protocol, typically used by the business-layer to provide user-defined methods/services to manipulate an object. For example look at the names of the services for accessing a book collection
To get a book getABook()
Get the whole list of books listAllBooks()
Find a book by name searchABook(String name)
Update a book's details updateABookDetails()
On the other hand, REST is representational state transfer which transfers the state of a web-resource to the client using underlying existing HTTP methods. So the above services for accessing a book collection would look like
To get a book /book(HTTP GET)
Get the whole list of books /books(HTTP GET)
Find a book by name /book?name={search}(HTTP GET)
Update a book's details /book/{bookId}(HTTP PATCH/PUT)
4. How to make a correct choice of architecture?
Spot the diversity of the application user groups and usages: This will help to understand the platform(web/mobile/IoT/etc), nature of the application and session-management.
Determine the estimated/required throughput: This will help you to understand the scalability requirements.
How frequently and who will be maintaining the application: This will help to gauge the application and technology complexity, deployment cycles, deployment strategy, appetite for downtime, etc.
In conclusion, always follow the divine rule of KISS: Keep it simple, stupid.
1.)
A webapplication is for H2M communication a webservice is for M2M communication through the web. The interface of the service is more standardized, more structured, so machines can easily use it and parse the messages.
I don't think it matters where your service consumer is, it can run in a browser or it can run on the server. As long as it can communicate with the service on a relative safe channel it is ok.
You design a service usually to decouple it from multiple different consumers, so you don't have to deal with the consumer implementations. This makes sense usually when you have potentially unknown consumers programmed usually by 3rd party programmers you don't even know or want to know about. You version the service or at least the messages to stay compatible with old consumers.
If you have only a single consumer developed by you, then it might be too much extra effort to maintain a service with a quasi-standard interface. You can easily change the code of the consumer when you change the interface of the service, so thinking about interface design, standardization, backward compatibility, etc. does not make much sense. Though you can still use REST or SOAP ad hoc without much design. In this case having a RESTish CRUD API without hypermedia is a better choice I think.
2.)
I think both are good, I would say backend in your scenario.
I am learning about microservices and I don't understand what the real difference
between creating a REST API and creating microservices?
I’m working in Go, but my question applies over all languages.
The Microservices approach is about breaking your system ("pile of code") into many small services, each typically has its own:
Clear business-related responsibility
Running process
Database
Code version control (e.g. git) repository
API (the protocol how other services / clients will contact the Microservice)
UI
The services themselves are kept small so as your system grow, there are more services - rather than larger services.
Microservices can use REST, RPC, or any other method to communicate with one another, so REST or an API is really orthogonal to the topic of microservices...
Reference: What is an API? In English, please.
API = Application Programming Interface
Microservices = an architecture
In short
Microservice should expose a well-defined API.
Microservice is the way you may want to architect your solution
API is what your consumers see.
You can expose API without microservices in the backend (in fact, most non-training scenarios don't require microservices).
You may want to read http://samnewman.io/books/building_microservices/ before you decide on using microservices (unless this is for training purposes).
Microservice is well defined when you are following SOC - seperation of Concern on the entity/domain level ,where each entity / domain are independent of any other service.
for example user service will only be responsible for storing, updating and deleting user related informations.
Microservice backend and frontend microservice can further be splitted in 2 parts
frontend microservice which exposes rest endpoint just like Web API
backend microservice which actually perform all the operations.
Rest API is more of endpoints exposed to outer world and can be used with microservices as well, as explained above.
The majority of the answers is based on the old-school understanding of API as a programmatic interface. Nowadays, this meaning is melted and start confusing people becuase some developers started (for simplicit or by mistake) interpred the API of an application as the application per se. In such case, it is impossible to distinguish between the modern API and Microservices. Nonetheless, we can say that an API-application can comprise many Microservices, the most of which interact within the application via Microservice's APIs while others may expose their APIs as Applications's APIs. Also, a Microservice (as a service) may not include other Microservices (services), but may orchestrate a composition of Microservices via API-bases invocations. Applications may contain Microservices but, in the best practices, may not contain other Applications.
Microservices
A microservice architecture is about slicing an application logic into small pieces or "components" that can act between them and/or be exposed through an API.
API
A (web) application need to design the business logic with all set of object entities (model) and possible operations on them.
An (Application Programming Interface][https://en.wikipedia.org/wiki/Application_programming_interface) is a way of making the requests to an application by exposing specific entry-points that are in charge of invoking the appropriate application operations.
ReST(ful) APIs
("ReST" as in Representational State Transfer) are APIs complying with at least these 5 constraints:
User-interface is distinct from data storage and manipulation (Client-Server architecture)
No client context is stored on the server ("stateless")
Server responses must, implicitly or explicitly, define themselves as cacheable or not
Client does not have to be aware of the layers between him and the server
Response/request messages must be: be self-descriptive; allow to identify a resource; use representations allowing to manipulate the resources; announce available actions and resources ("Uniform interface").
"The real difference"
So, while these notions are obviously related, they are clearly distinct concepts:
Being ReSTful or not, an API exposes operations provided by a server that might (but not necessarily) be shelled into smaller components (microservices).
Also, while a typical web (ReST)API uses the HTTP protocol between the client and the server, components within a microservice architecture might communicate using other protocol(s) (e.g. WAMP, AMQP, JSON-RPC, XML-RPC, SOAP, ...)
In layman's term, if you have a web API server and you split them into several independent mini servers, use a proxy-server and load-balancer to clusterize them, and (optionally, give each a separate database entity), that is a microservice architecture.
I'm looking for architectural patterns of server-side software, particularly web apps, that have been used for good reason in the real world. Here are some I can think of:
single-server: all parts of the app run on the same server (database, app, web server listening to port 80 etc.)
simple 2-tier: database runs on single server "DB", all other parts in an "appserver" tier, which may contain any number of servers. The tiers communicate via ODBC or such.
of this, variations (how many? can we enumerate them?) include single-master/multiple-slave DBs servers, and multi-master DB servers
3-tier: database runs on one tier, business objects and logic run on a second tier, presentation on a third tier, where 1 and 2 communicate via ODBC and 2 and 3 via some form of remote calls (e.g. RMI)
I seem to recall from some presentation that at one point, eBay had an architecture that had an app tier generate XML, which then was transformed into HTML in a separate tier. Is that common or an oddity?
a bunch of web apps use memcachedb or such to speed things up. A set of caching servers are arguably another tier perhaps?
Could you help me enumerate some of these patterns, or point to places where some have been described?
You might enjoy the decade-old but still relevant classic Building a Large-Scale E-commerce site with Apache and mod_perl. Their tiers were:
Load balancers
Reverse proxies
Web/app servers
Database servers
This is still the blueprint for large-scale sites. Even larger web-scale sites may need something more arcane, but this is the foundation for understanding even them.
Note that they used mod_perl, which means their web servers were their app servers. If you were using Java at that time, you would have run the app servers as a tier behind the web servers (and by 'web servers' i mean Apache, handling HTTP parsing, TLS, and static files; fetching and carrying, but no logic), and connected them with AJP. You might still do that today, but you would be more likely to just use the app servers as your web servers (ie no Apache at all, just JBoss or similar). App servers are now solid enough to do this, and you can rely on the reverse proxies and a content distribution network to do most of the fetching and carrying anyway.
As for a caching tier, the reverse proxies are a caching tier in front of the app servers, but they did app-level caching on the app server machines, with a federated cache (you'd use memcached or similar for this today). I think that's still a viable option today. I don't see a reason to partition your app-tier servers into dedicated app and cache servers; i'd be interested to hear of reasons to do that.
I don't think splitting the presentation and business logic in the app tier is an idea that ever really took off. Some projects probably do it, but i would imagine because of they have architecture astronauts in charge, rather than for any good reason. That said, it is common to have an app tier that makes heavy use of service tiers further back (this is SOA, i guess), and the ultimate extension of that is essentially a presentation/logic split, but with heterogenous logic servers, and the presentation server very much being in charge.
I have heard a lot of people talking recently about middleware, but what is the exact definition of middleware? When I look into middleware, I find a lot of information and some definitions, but while reading these information and definitions, it seems that mostly all 'wares' are in the middle of something. So, are all things middleware?
Or do you have an example of a ware that isn't middleware?
Lets say your company makes 4 different products, your client has another 3 different products from another 3 different companies.
Someday the client thought, why don't we integrate all our systems into one huge system. Ten minutes later their IT department said that will take 2 years.
You (the wise developer) said, why don't we just integrate all the different systems and make them work together? The client manager staring at you... You continued, we will use a Middleware, we will study the Inputs/Outputs of all different systems, the resources they use and then choose an appropriate Middleware framework.
Still explaining to the non tech manager
With Middleware framework in the middle, the first system will produce X stuff, the system Y and Z would consume those outputs and so on.
Middleware is a terribly nebulous term. What is "middleware" in one case won't be in another. In general, you can expect something classed as middleware to have the following characteristics:
Primarily (usually exclusively) software; usually doesn't need any specialized hardware.
If it weren't there, applications that depend on it would have to incorporate it as part of their application and would experience a lot of duplication.
Almost certainly connects two applications and passes data between them.
You'll notice that this is pretty much the same definition as an operating system. So, for instance, a TCP/IP stack or caching could be considered middleware. But your OS could provide the same features, too. Indeed, middleware can be thought of like a special extension to an operating system, specific to a set of applications that depend on it. It just provides a higher-level service.
Some examples of middleware:
distributed cache
message queue
transaction monitor
packet rewriter
automated backup system
Wikipedia has a quite good explanation: http://en.wikipedia.org/wiki/Middleware
It starts with
Middleware is computer software that connects software components or applications. The software consists of a set of services that allows multiple processes running on one or more machines to interact.
What is Middleware gives a few examples.
There are (at least) three different definitions I'm aware of
in business computing, middleware is messaging and integration software between applications and services
in gaming, middleware is pretty well anything that is provided by a third-party
in (some) embedded software systems, middleware provides services that applications use, which are composed out of the functions provided by the hardware abstraction layer - it sits between the application layer and the hardware abstraction layer.
Simply put Middleware is a software component which provides services to integrate disparate systems together.
In an complex enterprise environment, there are a number of challenges when you need to integrate two or more enterprise systems together to talk to each other. Normally these systems do not understand each others language as they are developed on different platforms using different languages (like C++, Java, Cobol, etc.).
So here comes middleware software in picture which provides services like
transformation of messages formats from one app to other,
routing and enriching messages besides taking care of security,
encryption,
validation and
applying different business rules to these messages.
A typical example of middleware is an ESB products like IBM message broker (WMB/IIB), WESB, Datapower XI50, Oracle Fusion, Mule and many others.
Therefore, middleware sits mostly in between the service consuming apps and services provider apps and help these apps to talk to each other.
Middleware is about how our application responds to incoming requests. Middlewares look into the incoming request, and make decisions based on this request. We can build entire applications only using middlewares. For e.g. ASP.NET is a web framework comprising of following chief HTTP middleware components.
Exception/error handling
Static file server
Authentication
MVC
As shown in the above diagram, there are various middleware components in ASP.NET which receive the incoming request, and redirect it to a C# class (in this case a controller class).
Middleware is a general term for software that serves to "glue together" separate, often complex and already existing, programs. Some software components that are frequently connected with middleware include enterprise applications and Web services.
There is a common definition in web application development which is (and I'm making this wording up but it seems to fit): A component which is designed to modify an HTTP request and/or response but does not (usually) serve the response in its entirety, designed to be chained together to form a pipeline of behavioral changes during request processing.
Examples of tasks that are commonly implemented by middleware:
Gzip response compression
HTTP authentication
Request logging
The key point here is that none of these is fully responsible for responding to the client. Instead each changes the behavior in some way as part of the pipeline, leaving the actual response to come from something later in the sequence (pipeline).
Usually, the middlewares are run before some sort of "router", which examines the request (often the path) and calls the appropriate code to generate the response.
Personally, I hate the term "middleware" for its genericity but it is in common use.
Here is an additional explanation specifically applicable to Ruby on Rails.
Middleware stands between web applications and web services that natively can't communicate and often are written in different languages/frameworks.
One such example is OWIN middleware for .NET environment, before owin people were forced to host web apps in a microsoft hosting software called IIS. After owin was developed, it has added capacity to host both in IIS and self host, in IIS was just added support for Owin which acted as an interface. Also it become possible to host .NET web apps on Linux via Mono, which again added support for Owin.
It also added capacity to create Single Page Applications, Owin handling Http request/response context, so on top of owin you can add authentication/authorization logic via OAuth2 for example, you can configure middleware to register a class which contains logic of user authentification (for ex. OAuth2 implementation) or class which contains logic of how to manage http request/response messages, that way you can make one application communicate with other applications/services via different data format (like json, xml, etc if you are targeting web).
Some examples of middleware: CORBA, Remote Method Invocation (RMI),...
The examples mentioned above are all pieces of software allowing you to take care of communication between different processes (either running on the same machine or distributed over e.g. the internet).
From my own experience with webwork, a middleware was stuff between users (the web browser) and the backend database. It was the software that took stuff that users put in (example: orders for iPads, did some magical business logic, i.e. check if there are enough iPads available to fill the order) and updated the backend database to reflect those changes.
It is just a piece of software or a tool on which your application executes and rapplication capabilities with respect to high availability,scalability,integrating with other softwares or systems without you bothering about your application level code changes .
For example : The operating system on which your application runs requires an I.P change , you do not have to worry about it in your code , it is the middleware stack on which you can simple update the configuration.
Example 2 : You experience problems with your runtime memory allocation and feel that the your application usage has increased , you do not have to much about it unless you have a bug or bottleneck in your code , it is easily achievable by tuning middleware software configuration on which your application runs.
Example 3 : You have multiple disparate software and you need them to talk to each other or send data in a common format which is understandable by all the systems then this is where middleware systems comes handy.
Hope the information provided helps.
it is a software layer between the operating system
and applications on each side of a distributed computing system in a network. In fact it connects heterogeneous network and software systems.
If I am not wrong, in software application framework, based on the context, you can consider middleware for the following roles that can be combined in order to perform certain activities in between the user request and the application response.
Adapter
Sanitizer
Validator
I always thought of it as the oldest software I have had to install. The total app used a web server, a database server, and an application server. The web server being the middleware between the data and the app.
Why do we use three tier architecture?
Here are a few possible reasons: client/server doesn't work well over the Internet, doesn't scale as well, and is harder to secure.
In the web development field, three-tier is often used to refer to websites, commonly electronic commerce websites, which are built using three tiers:
A front-end web server serving static content, and potentially some are cached dynamic content. In web based application, Front End is the content rendered by the browser. The content may be static or generated dynamically.
A middle dynamic content processing and generation level application server, for example Java EE, ASP.NET, PHP platform.
A back-end database, comprising both data sets and the database management system or RDBMS software that manages and provides access to the data.
The End-To-End traceability of n-tier systems is a challenging task which becomes more important when systems increase in complexity. The Application Response Measurement defines concepts and APIs for measuring performance and correlating transactions between tiers.
To keep the Internet away from machines that have no business being there.
Internet | Firewall | Load Balanacer | switch | <-> Web <-> Application <-> Database