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Implementation of feature flags in C#

Feature flags are something I often use but never really gave much thought about it until this new project I'm working on started.
I usually implement it with lots of keys in my web.config file but this approach has two major drawbacks:
When changing a value inside web.config the application pool is restarted - This can be a problem in a heavy access environment
Having too many keys in the web.config file is confusing and can get pretty messy
What's the best way to overcome these problems?

I would suggest using IoC to abstract away the implementation of your feature flags - all your code needs to access is something along the lines of IFeatures.IsEnabled("FeatureA"). Once you've done this, you can choose the most sensible implementation - some suggestions below:
web.config implementation (compatible with what you have now)
Database implementation (with cached values, possibly using SqlDependency if you want to work on a web farm)
Separate configuration file implementation (cached, but using a FileSystemWatcher to check for changes to the config file and load them without needing to restart the app pool). This allows for the case when you need features defined before you need your DB.

You don't have to store feature flags in web.config.
An option is to store them in a database - this has the added benefit of working well in a web farm.
Note that with feature flags, once you are in a position that a feature will be either permanently on or off (say when transitioning from widgetA to widgetB, and you will no longer need any widgetA code), you should be removing the feature and associated flag. This will help with managing the feature set.

If you want add feature flags to your C# applications I would not recommend creating your own feature flag solution but rather to use one of the several feature-flag-as-a-service providers which are out there that can directly integrate with C# right out of the box.
One such solution is Floodgate which has an SDK for .Net which you can install and be up and running with using feature flags in your application in next to no time.
Disclaimer, my name is Eugene and I'm the founder of Floodgate. That being said my advice is the same no matter what feature flag provider you decide to use.

Auditing with C# and .NET

I have a web application, and I would like to audit most of the users actions on the application, for example login, insertion to db, update to db, fired exceptions, etc.
One of my senios suggested using a queue for faster performance, so you just enqeue an event and it is then processed automatically without having to wait for it to be processed.
What are your suggestions? How should I process them? Enqueueing them is no problem, but I'm not sure how they will be processed then without no body calling a method.
I am using C# with .NET 4.0

I've been working on a library that can probably help.
Audit.NET and its extensions to audit different systems (WCF, MVC, WebApi, EF) and store logs in different data storages (SQL, MongoDB, DocumentDB, File, EventLog) will give you the flexibility to configure what do you want to audit and where do you want to store the audit logs.

I would simply recommend an off the shelf logging framework that is stable and supported. Have you considered a logging framework, like log4net?
You could write a custom appender for logging into MSMQ if you'd like.

An alternative logger is called TracerX. It is written in C# and fast and flexible. Because the source code is available it means you can modify it as you wish to suit your needs. It comes with a viewer that allows for filtering the output.
https://github.com/MarkLTX/TracerX and an article on how to use it:
http://www.codeproject.com/KB/dotnet/TracerX.aspx

Two topics of interest actually:
Asynchronous logging
Aspect Oriented Features
Asynchronous logging may speed-up heavy processing 100-fold. Use a writer thread that dumps the queue into log sink every,say 100ms however that Logging engine must be deterministically started and stopped so it can flush the sinks on application stop.
Aspect Oriented Programming addressed your cross-cutting concern - audit/log calls shall be invoked in desired operation prologues/epilogues - look at PostSharp project.

(Little late on the answer, this post shows up high in google, so I thought it may be worth looking at some of the options)
If you are looking to actually audit. (By this I mean to record that an action took place, who did it and when, and for that auditable log to be able to be used as evidence to an external auditor)
(Debug Logging vs Auditing logging)
If so, you can consider some options, such as:
use an Audit logging library
adopt an EventStore database
use a logging library that fails loudly
1. using an audit library
Audit.NET has already been mentioned here and has an impressive number of downloads and is very feature-rich
auditable - an alternative to the above (disclaimer, its written by me)
both are pretty cool, as they allow you to bring your own datastore
2. Eventsourcing
EventStore
Postgres with Marten
The design here (which can impact your architecture to embrace Events) is that Events are immutable, and if you store them then you have an auditable store of things that happened in your system
note this does not look to solve the question above, but it does solve how to audit, so I have mentioned it
3. Logging library
Serilog - Issue
you have to confirm that the logging library if it fails to add an Audit Log, it will throw an exception.
if it does not do that then you will be missing auditable logs, which then you cannot build trust with your Auditors
Side note 1 - with options 1 and 3, you may need to ensure that the log is written in the same transaction as your primary data store. to ensure that all of the information is ACID. (this is similar to the issue people have with publishing an event which is outside of the database transaction)
Side note 2 - that audit logs should be able to identify who did what, so you may/should need to encrypt the datastore they eventually end up in.

NHibernate in C# application, how to manage session

I'm new in NHibernate world and I'm starting to build a simple C# Windows Form Application that imports some XLS files into a DB (SQL2008), elaborates data and than exports a CSV file.
I've tried to search some examples to how use and manage NHibernate session; some of them are useful for Web Application. I've seen that in MVC Application the NHibernate session is created on Application Start, but I can't understand when I must create the NHibernate session into a Windows Form Application.
Anyone can help me?
Thank you!

Per the feedback I'll suggest that you look into using SSIS for this kind of work. Besides being designed for ETL processes like these SSIS can also be re-executed as needed and there's no need for custom code at all. Though if you want, it's not hard to write .NET code run SSIS packages as necessary. Here's an example. Beware though that SSIS APIs still often carry DTS prefixes. DTS (Data Transformation Services) is the precursor to SSIS (SQL Server Integration Services) and much of the technology is reused.

First of all, I don't think you are using the right tool for the job.
But if still want to use NH for learning purposes, these are my advises:
I highly recommend this lecture:
http://msdn.microsoft.com/en-us/magazine/ee819139.aspx
Ayende talks about most of the issues about session handling in non-web scenarios.
What we used to do is to follow a pattern-like Model-Per Form. A Model contains a session, but the model lifetime is tied to the life time of the form. This prevents having one session per-application which a very bad decision, in fact Fabio Maulo (NH Lead) says is like having a time-bomb in your application.
Goods new this is not the only approach.
Fabio Maulo and a very smart guy named Gustavo Ringel came up with this:
http://fabiomaulo.blogspot.com/2009/01/aspect-conversation-per.html
http://gustavoringel.blogspot.com/2009/02/unhaddins-persistence-conversation-part.html
Good news is not all theory, unNHAddins has a fully functional example of this concepts.
HTH

For a start I wouldn't recommend NHibernate for this scenario - imports/exports and multiple data stores are not really it's thing.
That said... Web applications generally create the NHibernate Session per page request (e.g. in the Session Start event, or as an action filter). The session factory is usually created in the Application Start though.
For a windows forms application you might want to take a look at the 'unit of work' pattern. Your session would probably want to follow this.

How to instrument code for logging C#

I'm wondering if there's any way of having some sort of Aspect-Oriented way of setting up logging of C# code. Or if the code could be instrumented for automatic logging.
At the moment the code is riddled with Log("Enter method XXX") and Log("Leaving method XXX") which make maintenance really tedious.
Ideally I'd like to have something that does the logging automatically the same way as the libraries are instrumented for profiling.
The next best thing would be to have some custom attributes maybe that I can tag my methods with. These would put some logging code on entrance and exit of the method.
And if the solution were compatible with the EntLib that would be perfect :)
Cheers.

If you're using the Enterprise Library, you have everything you need. Take a look at this article: http://www.codewrecks.com/blog/index.php/2009/01/31/unity-and-aop-in-enterprise-library/

You could use Log4PostSharp. I am not sure though what the future of this looks like as PostSharp went commercial.

What your referring too is a cross cutting concern, and not only affects your application but other applications that you might install at your establishment. The Enterprise Blocks are great and the inversion of control principal does help a lot with extracting repeating code from out of the system. However there is no way of logging without deciding some place in your code that you wish to record the event. for example exceptions, logging in, logging out, db actions, restricted actions etc. If you go the Enterrpise route its all done through configuration files and policies.
In the solutions I have provided, I have moved the logging functionality outside of the application space and it now sits aside every piece of code that I develop, ready and waiting to do the logging for me. On the last project I used a combination of Enterprise Blocks and Couchdb. Couchdb really helps with the aspect side as it works using REST and Json without involving itself too much in your application writing an interface to the log files is just a matter of a bit of HTML, it really is a fire and forget type affair, until that bad ol day when you need to scour the logs :)
The only problem that I have seen in applications where you automate the logging is that you use some sort of delegate process and pass things into them, which increases stack space. But this is so trivial that its beyond reason.
Program to interfaces and defined interfaces and you should be okay.

I remember something regarding Interceptors / Proxying to log entry/exit of methods.
Stack Overflow question - How do I intercept a method call in C#?
and check out this blog (ref'd in the same question) - http://madcoderspeak.blogspot.com/2005/09/essential-interception-using-contexts.html

Logging Framework, a good idea?

First of all, apologies for the subjective sounding title. This is intended as a direct question.
At present I am working on a suite of tools:
A C# Windows Service, to primarily
maintain an Oracle database.
A C# Windows Service, (which will be
used on multiple node sites) to
process content of the database.
An ASP.NET web interface to
facilitate management of the overall
"system"
Currently the tho Windows Services have been developed as Console Applications (to ease debugging/development) and I am in the midst of converting these to Services. After testing for a couple days now with these services, I'm finding that I would like to increase the granularity of my logging. I'm finding that I miss Console.WriteLine() and I would like to provide an alternate log source like a flat-file for this type of output. This has lead me to think, "Should I be using a framework, or have I got enough?"
The reason I have mentioned the aspects I am developing is to provide insight to my situation. A "Core" DLL has been created, common across all components, abstracting the interaction layer between the applications and database. It is within this DLL that a class has been created which will attempt to "log to a table in the database" else on fail "log to local Event Log". This is it, that's the extent of logging.
Throughout the aforementioned tools, there are multiple instances of logging not dissimilar to:
Log.LogError("Code", e.Message + "\n" + e.StackTrace);
Although quite basic, this method does make use of reflection to Identify the source of the error.
My Question
Looking at my current logging solution it appears "sufficient" in terms of what it does and how it is integrated with all my solutions. However, I've been looking at logging frameworks (Notably log4net) and their features impress me. The ability to, if needed in the future, add another output format (such as an SMTP server) sounds kind of cool to me! :)
What I would like to know are the benefits of moving to a framework (like log4net)? The extent of how much I will have to adapt my code? Whether or not I am just looking at the greener grass on the other side? And finally, but probably most importantly, am I doing the right thing? Should I just add the ability to my Log class to "LogDebug" and be done with it? The last thing I would want to do is completely overhaul my suite, just for a "basic" feature, but if there are other benefits (to design, reliance, good practice? etc.) I'm interested.
Thanks,

Yes. Using an existing, proven logging framework (such as Log4net) is a good idea.
Log4Net is configurable at runtime (great for tracking down issues in production code).
As a commenter pointed out, it's also very simple to use.

Proper logging is especially beneficial when running code on multiple remote systems, as far as I recall, log4net will let you send your logs to a remote syslog server without much coding overhead (meaning you can view your logs from all machines in one centralized place) doing this will massively reduce the time it takes you to get information relating to a bug or problem with the system, and should also give you an indication of how prevalent the issue is.
As mentioned in other posts, log4net also allows for multiple appenders and multiple log levels, so determining where you want certain log information (i.e. in a database or in a local flat file, hey log4net even lets you spit logs out over telnet) to be stored is an absolute doddle.
As for implementing it, there are several good sites talking you through the setup. How you actually make use of the logging objects that log4net gives you is an architectural choice, but you could simply change the constructor of an object to take a log4net object and from within this object, just use the log4net object as you would Console.WriteLine.
I find the tutorial series here particularly useful, and it'll also go in to more depth than I can here about the benefits and the different ways of configuring log4net.

Yes, you definitely want to use a logging framework. A logging framework will allow you to:
Set the logging levels for the different logger instances.
Set the "appenders" or output for each of the different logger instances.
Perhaps, more importantly, if you use a logging framework, it is very easy to swap out one implementation of the logging framework for another (perhaps a null implementation that simply discards messages); whereas, if you write all your logging statements, directly, swapping out the implementation will be a nightmare.

I think you should use Log4net, simply because it's always better to reuse than to build your own thing. log4net has been used by a lot of developers and are pretty matured.
Think about your maintenance prospect; one or two months down the road, you might need to tweak your custom logging class a bit, to add some multithreading support etc. And when you are fixing the bugs arose from your logging class, you will miss Log4net.

Well one of the bigger benefits is not having to maintain the code yourself. Most of the time, logging frameworks have a lot more functionality than your own solution. Because they are so focused on logging, those frameworks usually are pretty complete in the both functionality and ways to implement it. And then there's reliability; there's nothing worse than a logging framework that's not logging anything because it's bugged. ;)
Take for example ELMAH for ASP.net applications. It also includes notifications, exports to various target formats, etc. Things that are pretty handy but you'll never build yourself unless you really need it.
How many changes to your code are needed obviously depends on both your code and the framework of choice. It's hard to say anything about that.

I am going to give a shout out to NLog (http://nlog-project.org/home) as it doesn't suffer from the 'Straight Java Port - then rewrite' syndrome of most oss .Net libs.
Some key benefits for us were the very fast Logger.IsFooEnabled (volatile read) and the overall performance of the system.
To each its own though, but I personally prefer NLog for my projects (and some of my clients too).
Cheers,
Florian

The advantage of using a good logging framework like Log4Net is that they have a small impact upon your code in terms of lines of code that you have to alter (in other words you only have to alter each existing logging line).
Also, if you are concerned about altering your code if you change frameworks, or if you feel you want to roll your own, then you could always create your own interface to a logging framework. Then you only ever have to change your code in one place after that.

I think sysadmins expect services to log to the application event log in windows.
Look up System.Diagnostics.EventLog, although log4net will write to that too..

The initial statement in the log4j website might help in some of your questions, the underlying principles are the same of log4net:
With log4j it is possible to enable
logging at runtime without modifying
the application binary. The log4j
package is designed so that these
statements can remain in shipped code
without incurring a heavy performance
cost. Logging behavior can be
controlled by editing a configuration
file, without touching the application
binary.
Using a logger hierarchy it is
possible to control which log
statements are output at arbitrarily
fine granularity but also great ease.
This helps reduce the volume of logged
output and minimize the cost of
logging.
In this case there's clearly no need to reinvent the wheel. Most Logging frameworks are somewhat straightforward, so the extend of changes will most likely depend on the size of your existing programs.

if you write your logger class properly it will be easily expendable to any of your needs. Any framework could impress you with many features but another framework is another variable in your debugging process as it can give you an error that does not exists or can make an error by itself in combination with your application. If you are ready to make beta testing for open source software project this is fine...
In your place i would write log class with ability to extend it features you find interesting to you project based on the list of features known frameworks have. I don't see any problem to log something to file and then send it over smpt, just one small function does the job.
Moreover, you can write your own class which will be pretty abstract and put your basic code in there, if you will ever need to use external framework for testing you class would be able to use it with minimal impact on code. Just take a look how there frameworks are implemented on the code level.
think of that you will need to learn how to properly use these frameworks when your only needs for now to log very small part of it...