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.
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 unsure how to make use of event-driven architecture in real-world scenarios. Let's say there is a route planning platform consisting of the following back-end services:
user-service (manages user data and roles)
map-data-service (roads & addresses, only modified by admins)
planning-tasks-service
(accepts new route planning tasks, keeps track of background tasks, stores results)
The public website will usually request data from all 3 of those services. map-data-service needs information about user-roles on a data change request. planning-tasks-service needs information about users, as well as about map-data to validate new tasks.
Right now those services would just make a sync request to each other to get the needed data. What would be the best way to translate this basic structure into an event-driven architecture? Can dependencies be reduced by making use of events? How will the public website get the needed data?
Cosmin is 100% correct in that you need something to do some orchestration.
One approach to take, if you have a client that needs data from multiple services, is the Experience API approach.
Clients call the experience API, which performs the orchestration - pulling data from different sources and providing it back to the client. The design of the experience API is heavily, and deliberately, biased towards what the client needs.
Based on the details you've said so far, I can't see anything that cries out for event-based architecture. The communication between the client and ExpAPI can be a mix of sync and async, as can the ExpAPI to [Services] communication.
And for what it's worth, putting all of that on API gateway is not a bad idea, in that they are designed to host API's and therefore provide the desirable controls and observability for managing them.
Update based on OP Comment
I was really interested in how an event-driven architecture could
reduce dependencies between my microservices, as it is often stated
Having components (or systems) talk via events is sort-of the asynchronous equivalent of Inversion of Control, in that the event consumers are not tightly-coupled to the thing that emits the events. That's how the dependencies are reduced.
One thing you could do would be to do a little side-project just as a learning exercise - take a snapshot of your code and do a rough-n-ready conversion to event-based and just see how that went - not so much as an attempt to event-a-cise your solution but to see what putting events into a real-world solution looks like. If you have the time, of course.
The missing piece in your architecture is the API Gateway, which should be the only entry-point in your system, used by the public website directly.
The API Gateway would play the role of an orchestrator, which decides to which services to route the request, and also it assembles the final response needed by the frontend.
For scalability purposes, the communication between the API Gateway and individual microservices should be done asynchronously through an event-bus (or message queue).
However, the most important step in creating a scalable event-driven architecture which leverages microservices, is to properly define the bounded contexts of your system and understand the boundaries of each functionality.
More details about this architecture can be found here
Event storming is the first thing you need to do to identify domain events(a change in state in your system). For example, 'userCreated', 'userModified', 'locatinCreated', 'routeCreated', 'routeCompleted' etc. Then you can define topics that manage these events. Interested parties can consume these events by subscribing to published events(via topics/channel) and then act accordingly. Implementation of an event-driven architecture is often composed of loosely coupled microservices that communicate asynchronously through a message broker like Apache Kafka. Free EDA book is an excellent resource to know most of the things in EDA.
Tutorial: Even-driven-architecture pattern
There are 2 applications that need to communicate with each other. They are both running on the same PC.
Main Application (C#)
Helper Application (C#) -> launched from Main Application
Helper Application will modify some data used/contained by the Main Application. Can the helper application be a microservice? (not familiar with microservices, but I've saw this while checking on the net)
I found a helpful tutorial and was able to create a WCF Duplex Binding.
Now the Main Application and Helper Application can communicate.
I'm just wondering if this is a good solution (or a microservice is better??)
Can the helper application be a microservice? (not familiar with microservices...
Sure. "Microservices" is just the latest term that describes distributed component-based network computing. It goes back a long way to the days of (and possibly further) distributed COM (DCOM) and Corba; COM+ and finally service-orientated architecture (SOA). WCF used SOA as a best practice. In practice the only real difference between SOA and microservices is that the latter tend to adopt HTTP-REST-JSON as the transport/API/payload whereas the SOA generation is transport/payload neutral but generally using SOAP.
I found a helpful tutorial and was able to create a WCF Duplex Binding. Now the Main Application and Helper Application can communicate. I'm just wondering if this is a good solution (or a microservice is better??)
Well technically you are already using microservice/SOA.
I'm just wondering if this is a good solution
No. The problem with SOA/microservices on the same machine is that they are very chatty; have a high overhead; and their message payloads quite verbose. Both SOAP and REST utilise text messages (XML and JSON respectively) by default (which is large compared to binary).
If both client and server are on the same machine you are best to just use straight-up named-pipes and avoid WCF/REST. Communcation under named-pipes are binary and so are very compact; named pipes run in Kernal mode meaning it is very fast and as an added bonus when communicating locally, bypasses the network layer (as opposed to say TCP which will even for LOCALHOST).
I am working on an app that would greatly benefit from Arangos' multi-model capabilities. Considering the app needs for the back-end, I have concluded that most, if not all, of it could be served through a REST API as to aid cleaner design for future development and integration with others. The API would then be consumed by several web and mobile front-end frameworks to handle the rest of the logic. The project will be developed with Javascript for the whole stack, using the NodeJS ecosystem.
.
The question itself:
Should and could one use arangodb + foxx to create the complete back-end stack for serving a REST API, thus avoiding another layer/component in the stack? e.g. express/hapi/loopback etc.
.
Major back-end requirements:
Authentication with roles
Sessions
Encryption
Complex querying (root of my initial thought, as to avoid multiple hops between DB and back-end)
Entry parsing, validation and sanitization
Scheduled tasks
.
Mainly looking for:
Known design advantages
Known design limitations
"Hidden" bottlenecks
Other possible future regrets
.
Side question (that might answer some of the above): Could Foxx utilise some of the node middleware available via npm?
Thanks in advance for your time!
You can use ArangoDB Foxx as the sole backend of your application, however it is important to keep the limitations of Foxx (compared to a general purpose JS environment like Node.js) in mind when doing this.
You mention encryption. While ArangoDB does support some cryptography (e.g. HMAC signing and PBKDF2 key derivation for passwords) the support is not as exhaustive and extensible as in Node.js. Also when using computationally expensive cryptography this will affect the performance of the database (because unlike Node.js Foxx is strictly synchronous and thus all operations should be considered blocking).
ArangoDB does not support role-based authentication out of the box but it is perfectly reasonable to implement it within ArangoDB using Foxx (just like you would implement it in Node.js, except you don't need to leave the database).
For sessions there are generally two possible approaches: you can either use a collection with session documents (using ArangoDB as your session backend) or you can keep your services stateless by using signed tokens (Foxx comes with JWT support out of the box).
Complex/stored queries and input validation (using the joi schema library originally written for hapi) are actually some of the main use cases of Foxx so those shouldn't be any problem whatsoever.
Foxx comes with its own mechanism for queueing tasks, which can also be scheduled ahead or recur periodically. However depending on your requirements an external job or message queue may be a better fit. The good thing is you can get started with the built-in job queue right away and still move on to a dedicated solution if the need arises during development.
As for middleware and NPM packages: Foxx is not fully compatible with Node.js code. While we provide a lot of compatibility code and try to keep the core modules compatible where possible, a big difference is that Node.js is generally used to perform asynchronous operations while in ArangoDB all operations are synchronous.
If you have Node.js modules that don't use crypto, file or network I/O and don't use asynchronous APIs (e.g. setTimeout, promises) they may be compatible with Foxx. A lot of utility libraries like lodash work with no problems at all. Even if you find that a module doesn't work it may be possible to write an adapter for it like we have done with mocha (integrated into Foxx) and GraphQL (via the graphql-sync package on NPM).
In my experience it is a good approach to put your Foxx service behind a thin layer of Node.js (e.g. a simple express application that mostly just proxies to your Foxx API) and/or to delegate some parts of your backend to standalone Node.js microservices (e.g. integration with non-HTTP services like e-mail or LDAP) which can be integrated in Foxx via HTTP.
One more thing: while a lot of existing express middleware likely isn't compatible with Foxx because of Node-specific dependencies and async logic, ArangoDB 3 will bring a new version of Foxx with support for middleware using a functionally express-compatible API.
I'm just starting to port my sails application to a FOXX application so I can answer some of your questions.
Role based authorization in ArangoDB is probably at too high a level than you want. In our case, we use an external service to authorize various web and service based applications at a very fine-grained level (much lower than a vertex or an edge). My feeling is that Authorization at that level will require you to write it yourself in javascript. If it's just CRUD on a per collection basis, then it shouldn't require much effort.
For authorization and sessions, I would look at the FOXX example found at: FOXX authorization-session example
It's not clear what you're asking about encryption. If you're talking about SSL connections, then that is natively supported (see arangodb end-points). As for internal encryption, there is a javascript crypto module ArangoDb crypto
Entry validation, etc. is supported by the javascript joi package.
Complex querying... Absolutely and getting even better in ArangoDB version 3.x. Traversals can be chained (go down using one edge collection, then up using another).
You're right on the ball when thinking about efficiency. This is the main reason we're going from sails to FOXX. In our case, we filter query results based on permissions from our external service. This means that we can't use ArangoDB native skip and limit support if these attributes are specified by the client. In sails, we have to bring back results in chunks and collect until we hit the appropriate skip and limit values. By moving to FOXX, we save a lot of network and other resources. We tested this by having sails forward the request to our prototype FOXX implementation. This scaled much better than the sails post-processing setup.
You can use NPM modules with restrictions. See Javascript Modules
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.