I'm designing various parts of a network. My current thought on design for future software projects:
Webserver in a DMZ. This webserver has a hole punched through the firewall (On the sql port) to talk to an MSSQL database which is internal for all data management.
Question: Instead of having a hole in the firewall to talk to the database server, would it be better / more secure to have an internal web server hosting web services that applications in the DMZ can consume, with the database logic behind the web service ( a hole punched to talk to that webserver only. )
A webservices implementation would allow only one place for updating any API changes - which is why I'm considering it - though it would likely be slower than direct database and query access.
Any thoughts as to which is better?
EDIT: Realized that unless I put all application/business logic in the application layer, I would still need a hole punched into the firewall for sql. Since I want an added layer only for the API functions (those that affect all applications - such as "GetEmployeeByName"), I'd still need access to the DB from the DMZ...
Leaning toward the best answer being: Internal web service API server hosting web services - those are consumable by either all web servers in the DMZ, or via a proxy server in the DMZ. (so only one server needs an ssl port through firewall.) (And of course all internal servers would have access.)
There are many discussions about when three-tier architecture is a better model (here's one). You should be able to find more on Google.
Short answer: It's probably better to go with the app-tier service, if security and scalability are your goals. Be sure to focus on defense in depth as you develop all tiers and layers.
Long answer: It depends on your needs.
Edit in response to your edit: I would recommend putting most of your business logic in the app tier anyway, if it makes sense to do that. Your web server(s) should primarily be presentation.
Regardless of where you put the business logic, though, you should put all data access into the service - the web tier should only talk to the app tier.
Here's a beginning search to dig into the three-tier aspect. Here's a decent introduction for splitting of tiers and whatnot.
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it might be a simple question but as I couldn't find the best answer on google I would like to know your thoghts.
I'm thinking of changing a software I've made in WPF accessing its data from a local server to a cloud server (maybe Azure).
What's the best way, connect directly to the database or access through a service in the clould (that would have to be developed by me I guess).
Thanks!!!
In general, I would guard against directly accessing a database hosted in the cloud via a client application. You'll be exposing your database endpoint through the public internet providing a significant attack vector.
By using a service, you can limit that attack vector. The service itself is also 'exposed' but can be locked down (typically more effectively/easily) with authentication/authorization protocols like OAuth, AD, etc. AND the service itself would expose only the operations necessary for the client application, versus access to the complete database schema (should someone crack the password when the database is on the open internet).
You didn't mention if you were planning to use Windows Azure SQL Azure or your own database in IaaS. You can, of course, implement your own security via firewall, etc. on VMs hosted in Windows Azure, but that's another infrastructure task you'll need to accommodate, and if your client IPs change, etc., then managing that is not insignificant.
I think the answer to the question would be the same whether you'd be on Azure or not.
A service adds an abstraction layer between the application and the database, which may help with maintenance in the long term, but it does have a cost associated with it (in terms of initial effort) and some potentially performance penalties (although this does not have to be significant) so in the end you'll have to weight it according to the application.
I really do not think there's a one-size-fits-all answer to this.
I am building a desktop application that will be used on local network, with SQL Server as database.
This application would have around 50 users top at the same time. In what particular scenario would I need to use WCF service? Is it recommended to create a WCF service on the server computer where database would reside, so we connect to this server through WCF service, instead of connecting to the database directly? What is the recommended way to connect to SQL Server data and why?
Edit: Let me explain in more detail. I have used WCF Ria services before, so I know how they work. Lets assume that WCF services works in same way. The question was directed toward why would we use WCF instead of directly connecting to database? I didnt want to specify my current application requirement, since I would get a specific answer for specific requirement. My goal was to understand in general why and when would you yse one instead of another. And I have received satisfying answers so far.
It appears to me that general consensus is to use WCF only if there would be a demand of another type of application, which would use web access to get data from service. Also, if I understood correctly, from security point of view, there is no difference between the two.
There would be a statistical app in the future that uses web to provide read-only statistics to user, and naturally some service will be required for this task (application has no specific client in mind, it will be offered to lots of clients). Since I need some demo application to be done very rapidly for particular clients, then I am thinking to neglect the service part, and make a proper layering (WPF->VM->Model->EF, so later I would just insert service between the model and EF. I guess it should not take too much time to make WPF app running with inserted layer. I am also postponing the service because of next reason: since HTML5 is (going to be) main technology for web, and there is a possibility that SL will be abandoned as technology (which I have been using), the logical decision would be to choose HTML5 over SL. But since I am totally unfamiliar with HTML5 and its requirements, I am not sure if WCF service is the best choice for it, and this is also one of the reasons to postpone the decision of choosing the service type (along with requirement to make the desktop demo app as fast as possible).
I think a better way to consider the question is whether you should abstract your database and data access layer from the application using a service interface. You could use WCF and SOAP or you could use a REST based HTTP service, the choice of technology is secondary to whether the current or future requirements of your application indicate that an additional layer of abstraction is warrented.
Reasons you might consider using a service interface instead of directly connecting to the SQL database include but are not limited to:
Ease of supporting multiple operating systems/client UIs
Ability to evolve the data/service interface separately from your database schema
Isolate application from changes to database schema or location (you don't have to redeploy change to application, only change internals of the services it is calling)
If data could be used by other systems, you have a standard means of allowing these systems to interface with the data your application is managing
Reduced SQL database connection security concerns (only service identity connects to database, allowing you to use a variety of authentication/authorization strategies on the client side)
The trade off you are looking at is the time/cost/complexity of implementing a service interface versus the flexibility and mantainability benefits you will gain. You should evaluate the needs of your application and your customer before you make a decision on whether to connect directly to your data store using ADO.NET or use a service layer.
You should take a look at the Microsoft Service Layer Guidelines as they cover a lot of the considerations to take into account.
Unless you need to create a reusable service, I can't think of a reason to add a WCF layer, unless you are just looking for a reason to do it. I think you can just go with some sort of ORM like EF or nHibernate and be happy.
The main reason for WCF is security. If the client connects directly to the DB then the client must be given rights on tables. The client can hack into the connection and use TSQL directly. You must expose port 1433 to the network in a single tier application. With WCF there is not direct access from the client to SQL. It is not just more secure in general but you can have more granular security. .NET service code can enforce row level security. A table only has column level security. If this is business on a private network and you don't expect anyone would try and hack into your db then client connecting directly to the SQL server is easier to build. With server side service the other factor is a change to server side code is one spot so you don't have to update 50 devices.
I see two ways of going about feeding data to and from a mobile application.
First would be to directly connect to the database and perform queries directly.
The other option would be to build a REST API and indirectly interact with the database through a web service. There's a bit of a security hole here, which makes me think the former might be best.
I realize this doesn't touch specifically on a question about code, but moreso on the methodology of the scenario.
What are your thoughts?
The usual way would be through a REST API (or some other kind of web service / service layer).
Putting the database open in the wild, directly accessible from any outside device, is certainly a bigger security hole than using a service layer.
Plus, if your database is hosted by some web hosting company, there is a big chance that it's not even accessible directly from the web, only from the webspace you ordered with it (for security reasons!).
So you have no other choice than using a service layer in this case.
I'm looking to develop an application for Mac and iOS-devices. The application will rely on information stored in a remote database. It needs both read (select) and write (insert, update, delete) access to the database. The application will be a multi-user application.
Now I'm looking at two different approaches to access the database:
- via web service: the application accesses the web service (REST, JSON) which accesses the database. Authentication will be done via HTTP authentication over SSL (https).
- access the remote database directly over a VPN.
The app will be used by a maximum of let's say 100 people and is aimed at small groups/organizations/businesses.
So my question is: what would be the best approach to access the database? What about security and performance? What would a typical implementation for a small business look like?
Any advice will be appreciated.
Thanks
Using web services adds a level of indirection between the clients and the database. This has several advantages that are all due to the fact that the clients need to have no knowledge of the database, only of your web service interface. Since client applications are more complicated to control and update than your server side code, it pays to add a level of business logic on the server that lets you tweak your system without pushing updates to the clients. Main advantages:
Flexibility - you can change the database configuration / replace the data layer altogether and change nothing on the client apps as long as you keep the same web service interface.
Security - implement some authentication mechanism for your web services, and avoid giving clients access credentials to your database engine.
There are some disadvantages too: you pay for that flexibility by adding a level of complexity - it'd probably be faster to just code the database access into the clients and get done with it. Consider the web services layer as an investment that might pay dividends down the road. Whether it's worth it really depends on your business requirements and outlook.
Given the information you have provided, the answer is almost certainly web services, unless the VPN is fast.
If the VPN is fast enough to handle the traffic, you will save a lot of time, effort and expense by accessing the database directly from your application.
You can also provide remote access to virtual PC sessions, if that's your thing.
So it's all going to depend on what your requirements are. There are a lot of ways to do this, and each has its advantages and disadvantages. Making the right decision will require a fair amount of systems analysis, probably beyond the scope of a question posted on StackOverflow.
Please I need help.
I have project in which I need application which communicates with local DB server and simultaneously with central remote DB server to complete some task(read stock quotas from local server create order and then write order to central orders DB,...).
So, I don`t know which architecture and technology do this.
Web application, .NET WinForms client applications on each computer, or web services based central application with client applications?
What are general differences between this approaches?
Thanks
If you don't want to expose your database directly to the clients, I'd recommend having a web service layer in between. Depending on the sensitivity of your data and the security level of your network, I'd recommend either a web service approach (where you can manage the encryption of data yourself, and without need for expensive ssl certificates) or a web interface (which might be easier to construct, but with limitations in security).
I agree with Tomas that a web service layer might be good. However, when it comes to choosing between webforms or winforms I don't think your question includes enough information to make the choice.
I'd say that if you want a powerful and feature rich user interface and want to make development easy, Winforms is probably the way to go. But if you need it to be usuable from a varied array of clients and want easier maintenance and deployment, a web app might be best.
First, focus on the exact relationship between these databases. What does "local" mean. Right there on the user's desktop? Shared between all the users in their office? Presumably the local quotes (you do mean stock quotes and not quotas?) could potentiually be a little out of date relative to the central order server's view of the world. Does that matter? I place an order for 100 X at price 78.34, real price may be different. What is the intended behaviour.
My guess is that there is at least some business logic and so we need to decide where that runs. One (thick client) approach is to put that logic on the desktop, the desktop app then might write directly to the central DB. I don't tend to do this for several reasons:
Every client desktop gets a database connection. Scaling is not good, eventually the database gets unhappy when the number of users gets very large.
If we need a slightly different app, perhaps exposed to a different set of users via the Web or whatever, we end up reproducing that business logic.
An alternative approach (thin or browser based) keeps the UI on the desktop, but puts the logic on the server. The client can then invoke some kind of service. Now there's lots of possible ways of doing that, a simple Web Service or Rest Service will do the job. I hope it's clear that this service-based appraoch addressed my two points above.
By symmetry I would treat the local databases in the same way, wrap them in services. However it's possible that some more complex relationship between the databases exists and in which case you might need the local service layer to interact with the central service layer.
I'm touting the general pronciple of Do Not Repeat Yourself, implement each piece of business logic once.