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Are there any performance and/or other issues when hosting both a Web Api and WCF service in a single Windows service?

Initially when I built an application, there was only a requirement to expose an endpoint using WCF. Now, there is a requirement to expose another endpoint using REST therefore I have used .Net Web Api to do so. The WCF endpoint is hosted in a Windows service therefore I have hosted the Web Api endpoint in the same service. Are there any issues in doing so? Any performance considerations? After some exhaustive searching, I couldn't find any substancial information on the topic.

Are there any issues in doing so?
It may be better to expose the rest API via WCF using webHttpBinding rather than introduce WebAPI into the mix. I'm not aware of any problems this would cause per se, but in terms of solution simplicity I think it makes more sense to take advantage of WCF's multiple-endpoints-to-one-service-contract mapping capability.
I did consider this but I've read a lot of bad reviews about using WCF
to expose RESTful endpoints. Moreover, it appears Web Api is the
preferred technology as mentioned here:
WCF vs ASP.NET Web API
Agreed. If you were starting from scratch then I wouldn't hesitate recommending WebAPI over WCF (actually I would recommend using Nancyfx over WebApi any day of the week).
You can expose your service as HTTP with about 10 minutes work using WCF, assuming you wish to expose the same operations as are currently defined on your service contract, as you have already have the soap endpoint.
Plus you will end up with a simpler solution without the considerable bloat of asp.net/owin.

What is the advantage of using Web API in a ASP.NET MVC (5) project?

I am implementing an enterprise web application in ASP.NET MVC 5. In many situations I am writing AJAX gets and posts and communicate with the server app. Currently I am writing controller actions to serve those requests, typically returning with JSON result. The action methods parameter binding also seems work seamlessly when I passing JSON at client side.
I do not want to go far with a not appropriate practice, so the question arises, what could be the advantage to add Web API support to my project, and refactor my current ajax - controller practice?

There are few advantages according using WebAPI over MVC + Ajax:
Internal serialization
WebAPI has an internal serialization, which makes returning specific data much more easier, without your own extension method or making your controller dependent on the serialization framework library.
Action result helpers
You can use plenty of action result helpers like Ok(), NotFound(), InternalServerError(), which all return IHttpActionResult, what makes your code easier to read and maintain and clearly state your intention.
Action result abstraction
Using IHttpActionResult you can easy abstract result, which is helpful when unit testing your controllers.
Available to self-host
Using OWIN you can easily self-host your WebAPI project, what makes your application much easier to maintain and IIS-independent.
Native attribute routing
WebAPI has implemented attribute routing which makes all routing configuration much more easier(and helps when using feature-based architecture).
DI configuration improvements
Both WebAPI and MVC have their own composition roots and different DI implementation. Microsoft has introduced some improvements in WebAPI to make it easier to use and maintain.
I'd say that using MVC + Ajax was viable only when WebAPI didn't exist because there was the only option.

If your project clients needs data in multiple formats (json,xml,csv) or have chance to change in future Wep Api needs minimal configuration comparing to mvc. Wep Api returns data to client according to content negotiation (if client needs xml returns xml,if json return json according to request header ) but in mvc you need more code to satisfy that.You have to explicitly specify data format when writing action methods.(JsonResult,ActionResult,XmlResult)
Wep Api gives you more meaningful idea about what you are doing when you look at the code later.Comparing method signatures;
public List<Student> Get() has more meaning than public JsonResult Index().

Light weight & Easy to use.
Less data transfer between client and server.
Using webapi we can develop cross domain application.
Less configuration needed as compared to WCF.

It’s simple, scalable and robust because it supports all the MVC features such as routing, controllers, model binders, IOC container, action results, filter, or dependency injection as it is built on top of Asp.Net MVC.
Empower the developers by handing over control over the way HTTP protocol messages are sent and responded to.
Unit testing is easy as it support test driven development.
It provides ample flexibility in web API creation due to content negotiation and drives support for the ASP.NET routing.
Unlike WCF REST services, there is no need to define tedious configuration settings for different devices.
The architecture of web APIs is very light, which makes them a perfect alternative for the developers when they want to build applications for devices with limited bandwidth.
Web APIs are used to create non-SOAP-based HTTP Services, so if there is a requirement for web services, but not SOAP, then ASP.Net Web API is great to look for.
Supports different message format like json, plain text and xml.
Asp.Net Web API supports convention-based CRUD Actions since it works with HTTP verbs GET, POST, PUT and DELETE.

Difference summary WCF and Web API

I'm looking for the difference summary between ASP.NET MVC Web API and WCF Service.
I've seen this question What is the difference between Asp.Net Web API and WCF Service?
and this question WCF vs ASP.NET Web API too, but they don't summarize what I can achieve with the one, what I cannot achieve with the other.
Both can be contacted via url, I first thought that was a difference between them.
So in short:
What can I do with WCF what I cannot do with ASP.NET Web API and visa versa?

this list is by no means exhaustive.
Things WCF does that you cannot do (with ease) using Web API.
Supports SOAP based XML format.
Supports strongly typed data contracts.
Supports a single point of metadata information exchange using WSDL etc.
Supports varied bindings like TCP, Named Pipes, MSMQ, even UDP etc.
Supports varied hosting options like console apps, WAS, IIS, Windows Services.
Supports one way messaging, duplex, message queues out of the box.
Supports multiple authentication schemes like Windows, Forms, Certificates etc.
Things Web API does that you cannot do (with ease) using WCF.
Supports the full features of HTTP. (Uri based access, Http Requests/Response, Http Caching etc.) To do this in WCF you need to additional work to configure it as REST service etc.
Is Lightweight with minimal configuration.
Supports the Routing, Controller/Action MVC paradigm, Model Binding etc.
Basically Web API is an easy way to do RESTful services over Http without knowing much about Web services.
To do the same in WCF, you need to do additional work in terms of httpBindings, UriTemplates, Verbs etc. And that means, understanding WCF first. And then using WCF to implement a RESTFul service over http, which is what Web Api provides out of the box.

This is not a summary per se. Its a sort of practical guide I hope.
For me it ultimately boils down to how simple I want my front-end application code to look like, and also something to do with how to achieve maximum productivity.
Traditional WCF over http is SOAP based messaging protocol. You add a service reference in your project, and Visual Studio takes care of generating the proxy classes. And you work with the instance of the proxy classes. So when you are writing your front-end code, you have intellisense to help you. Don't be fooled. This is just the IDE making life simpler for you. Underneath its pretty complicated. But my productivity is boosted to a degree. I don't have to write proxy classes. Hence, this is what I'd opt for a c# based front-end.
Alternatively, if I had to deal with a Webapi endpoint, I do not have the luxury of any IDE generated proxy classes. Therefore I'd have write code for everything. Typically I use the HttpClient classes to talk to my web api end points. Hypothetically, I could write a proxy classes to talk to web api. But it isn't as simple as in your wcf case where they were auto-generated for you.
On another line or reasoning, if my front-end was JavaScript, then my only best bet is have the web service hosted over web api, rather than wcf. If I were to talk to wcf endpoints from Js, that would be a PITN.
So it ultimately rests on your product plan, design, project schedules, etc software development plan. All the best.

Web Service or web API for connecting a windows application to MVC 4?

After searching the entire day about what I should use, I'm not sure what option would be best for my needs so I hope someone with more experience could help me out.
I have a winforms application (c#) and a ASP.NET MVC 4 web application (c#).
I wish to connect these, the goal is to send and receive data from the database which I use in the MVC 4 project, but from within the windows forms application. The data I send from the windows forms application to the database, is then used by the MVC 4 web application.
I am entirely new to web services / Web Api's so I can't really decide what option would be best. Any help would be much appreciated..

If you already created MVC4 project then you can add actions to any controller
and return JSON data like below :
public JsonResult GetCategoryList()
{
var list = //return list
return Json(list, JsonRequestBehavior.AllowGet);
}
or you can create new project of MVC4 and select WEBAPI template . It will create webapi project for you .It will create with example .so it will easy for to create webapi.In webapi it return data automatically convert to xml and json as per request
The WCF Web API abstractions map to ASP.NET Web API roughly as follows
WCF Web AP -> ASP.NET Web API
Service -> Web API controller
Operation -> Action
Service contract -> Not applicable
Endpoint -> Not applicable
URI templates -> ASP.NET Routing
Message handlers -> Same
Formatters -> Same
Operation handlers -> Filters, model binders
Other Links

If you have an MVC 4 App already, it would be better to use Web API (RESTful service)
I assume you have some knowledge in building REST API (understanding of POST, PUT, UPDATE stuff)
It is simple in configuration and usage. All what you need actually is to create a new controller like:
class MyApiController: ApiController {
public Post(SomeClass item) {
....connect to db and do whatever you need with the data
}
}
You'll also should configure routing for Api.
And then in your winForms app you can simply use HttpClient class to perform api call.
HttpClient aClient = new HttpClient();
// Uri is where we are posting to:
Uri theUri = new Uri("https://mysite.com/api/MyApi");
// use the Http client to POST some content ( ‘theContent’ not yet defined).
aClient.PostAsync(theUri, new SomeClass());
Take a look at some implementation details right here:
Web Api Getting Started
Get started with WCF is not so easy as with Web API.

Given the tags you've used, my guess is that you're deciding between SOAP Web Services and WCF. Given these two, I say to go WCF. SOAP web services (as implemented in Visual Studio) are the older technology; still serviceable, but WCF can do everything an older SOAP service can do (including look exactly like a SOAP service) and more.
If you have a web service that connects your web server to your database server (these two things should be on different machines; your web server is exposed to the world by necessity, while your DB server should be locked down like Fort Knox), I see no reason why you shouldn't use that same service as-is for an internal WinForms application (using a LAN/VPN to access the service layer on the DB server). For a WinForms application that must access the data over the Internet, I would recommend reimplementing the service as a WCF service supporting secure encrypted data transfer. You can also set up the service endpoint to only accept HTTPS connections, and thus simply run your existing service through SSL/TLS.
What you choose will primarily depend on how much time-resources you can commit to resolving the problem; moving to HTTPS is a fast fix requiring little if any code changes, while reimplementing in WCF will take more time but will allow additional security measures beyond a simple secure tunnel.

Or something lightweight like Nancy: http://nancyfx.org/

We had some issues with MVC4 WebApi stuff and ended up using ServiceStack on the server side JavaScript/AJAX for web clients and RestSharp for thick clients.
One of our specific issues was the inability to auto generate documentation, significant performance differences, and better support for unit/integration testing.

Rather than advocate specifically WCF, I'd recommend WCF Data Services or OData, with the stipulation that you'll need to secure it. If you go for pure WCF, you'll see that you'll end up creating a lot of code to handle retrieving the info from a database, and then sending that information right back out to your clients. It doesn't sound that bad, at first, but after about 30 entities in a database, you'll quickly grow tired of a pure WCF solution.
OData is great, it uses Entity Framework, and it quickly opens data manipulation for an existing database or one you are going to make. It will save you a ton of development time, if you can make your service secure. The format of the data response is flexible. There are plenty of client libraries ported for other programming languages as well.
The steps for securing a service are pretty simple. Always deploy to https. Any login or registration methods , need to be post methods, that return a token (Encrypted value), or a unique secret that can be encrypted and sent back for any subsequent requests. It's better to use the token, and have an expiration on the token.. because otherwise both your service and your app whether mobile or desktop, need to have a shared encryption / decryption method.

how to make a service, SOAP web service in .net?

Please forgive me for this basic and a little theoretical question as I dont know much about web services.
I m not refering WCF service, I am reffering simple service in .net / C#. I want to know how to know is it soap or rest service ?
How we can change this type from Soap to Rest and vice versa ?
Thanks

XML Web Services (aka classic/legacy ASMX web services) should not be used for active development. If you must, there is a nice walkthrough on MSDN for adding Web references in more recent versions of Visual Studio (> 2005).
On the other hand, if your web service is truly Restful then you won't be able to create the equivalent of a service reference to it. You'll need to either use the HttpWebRequest, WebClient, or the new HttpClient from .NET 4.5 (also available from the Rest starter kit which is depreciated as well).
As an alternative if you are looking to implement a client that is able to handle both situations, I would recommend HttpWebRequest to POST to the SOAP (non-WCF) service. The problem with this method is you'll likely have to wrap the request in the SOAP wrapper yourself. Luckily there are examples of doing so on the net that you can at least use as a starting point.

ASMX services are build upon SOAP. REST is simply a HTTP based, You can access(or call) your business resources the way you access the normal URLs.
For ex in products catalog system, by using asmx you create set of functions to add,update,delete products. like addProduct(),updateProduct, etc..
But in REST, you will be having single point of access, like http:\mysystem\prodcuts. To retrieve,add,update,delete products, you will be using respective HTTP verbs (GET,POST,PUT,DELETE) on the same URL.
so,technically it's not possible to convert asmx(SOAP) service to rest...