We have a python web app that clients interact with and that web app directly interacts with a database. We now have the need to develop an API that merchants will use to get and post data from/in our database in JSON. Should we build the API as part of the web app, meaning that each request will pass through our python web app and then interact with the database or should it be separated?
Further considerations include scalability and the fact that in the future we’ll probably want to develop a mobile app or other services that will also need to communicate with the database. As such, we considered the possibility to build an API as the only point of interaction with the database.
However, we are deeply in the development of the flask web app and change it would mean an huge delay in our schedule and we just wanted to weight in the advantages and disadvantages of both solutions.
These two schemes summarize the options we are considering:
Option 1:
Option2:
As you said both options have advantages and disadvantages.
Option 1 gives you Separation of Concerns. The logic for interacting with your database is abstracted behind a single service. Changes to the type of database you use or the schema you use only requires code changes to a single service. For example, say your platform has expanded and you now wish to cache calls to your database. If you have an API, Web App, and Mobile App all communicating directly with the database they must all be updated to take advantage of the cache. These changes would likely also have to be orchestrated to be deployed at the same time. In reality this is going to involve downtime: most often you see this referred to as 'scheduled maintenance'.
However, Option 1 breaks the Single Responsibility Principle. A service should do a single thing and do it well. In Option 1 the service is responsible for both being an interface to the database and rendering HTML for the web app. Changes to the Web App require you to redeploy the service for the API even though the two are not connected.
The advantages and disadvantages for Option 2 are mostly just the opposites of the advantages and disadvantages for Option 1. Multiple services sharing a database can lead to inconsistency in the data, tight coupling (especially in deployment), and debugging being more difficult.
A common design pattern (which I'd recommend) is a slight modification of Option 1. An API sits in front of the database. This is the only service that interacts with the database. This setup should improve your scalability. It's easy to deploy duplicate APIs and then load-balance requests between them. Furthermore, caching database lookups or changing database technology entirely is a (relatively) simple task. Your Web App, or any other services you develop in the future, interact with the API instead of the database. Here you can reap the benefits of Single Responsibility. It is worth noting that with this design every request for your Web App will have to go through two services. However, the benefits of the design arguably outweigh a few extra milliseconds of latency.
One last thing: kudos for thinking about scalability this early on. You may take a hit now if your schedule is delayed but I think you'll be better off in the long term.
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
Since Lift is stateful, each subsequent request to a page/site must go back to the same server. Presumably that means that the front-end load balancer needs to keep track of which client is talking to which server.
How does that work out for hosting on places like Heroku/Elastic Beanstalk, where the load balancer is all done automagically for you by the service? I know if you are setting up all your machines yourself you can set the routing to do the correct thing, but how does it work on these PaaS type hosts where all this is meant to be done for you?
EDIT: Google App Engine would have the same limitations, if i am not mistaken?
Heroku will distribute requests between dynos (processes) evenly so I believe you would have to use some form of sessions serialisation for a stateful Lift app. I believe Elastic Beanstalk does have some facilities to support this however (as ELB does).
David Pollock writes about how to use Lift in a stateless way and also talks generally about the design of Lift in this area here.
Lift is not really intended to be used in a pure stateless mode, its possible, but its not where the framework excels. ELB does indeed have support for sticky sessions, which is the configuration you need to take up in order to use Lift successfully in nearly any environment.
More broadly, this "sticky session" functionality can be achieved with either software of L4 hardware balancing. You might be interested in chapter 15 of Lift in Action which spends a fair amount of time discussing this very subject and the various session serialisation strategies if you really want that.
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