Deployment and security options of custom code in SharePoint 2010

In SharePoint 2010 there are more ways to deploy custom code than in its predecessors, the reason is the introduction of the Sandboxed solutions. There are basically now three different ways to deploy custom assemblies:

• Full trust solutions/ Farm solutions - The assemblies are registered in the GAC and runs under full trust
• Partial trust solutions/ Web Application solutions - The assemblies are deployed to the bin folder of a specific Web Application
• Sandboxed solutions/ User code solutions - The assemblies (solutions) are deployed to the Site Collection gallery

These are the basic variants of how to deploy custom assemblies. There are actually a few variants of them, but more about them later. So which one should I use and when? Let's go through them all and look at the pros and cons.

Sandboxed Solutions

The Sandboxed Solutions runs inside the a special service, called Microsoft SharePoint Foundation Sandboxed Code Service, which is a completely and separate application domain than the SharePoint application pools. The Sandboxed solutions are monitored and if they consume to much resources or fails to many times SharePoint automatically shuts the solution down. The code running in a Sandboxed assembly does not have access to the full SharePoint API, basically it's just the classes from Site Collection level and below. The sandbox is also protected with a very minimal CAS policy which for example prohibits the user code solutions from calling web services, making database calls or accessing the file system.

Sandboxed solutions are deployed into the Solution gallery of a Site Collection and only access that Site Collection. They can be deployed without having any downtime of the farm or web application. Anyone within the Site Collection Administrators group can upload solutions to the gallery and activate them. Farm administrators controls how much resources each Sandbox can use and can also block specific solutions from running at all.

Pros	Cons
Can easily be deployed by Site Collection Administrators	Very limited CAS policy
Resource usage is monitored	* Current uncertainty about the monitoring stability
Secure	Hard to deploy in a farm
Great support in Visual Studio 2010
Only crashes the Sandbox if it blows

Farm Solutions

The Farm solutions or full trust solutions adds the assembly to the Global Assembly Cache, GAC, which means that they can run without any CAS policies, i.e. under full trust. The assemblies can be accessed from any application in the farm. Full-trust solutions are (was?) the most common way to install solutions since it is easy and requires no knowledge of for instance CAS policies. The code running in a full trust solution has the same access as the application pool account to the local server and can do almost what it want with the server. Deploying Farm solutions should only be done with code that you really trust.

Only farm administrators can upload new farm solutions to the configuration database and most often an application pool recycle is needed, especially when updating solutions.

Pros	Cons
Easy to implement	Only Farm Administrators can add new solutions (can be a pro also :-)
Great support in Visual Studio 2010	Downtime when updating
Runs in full trust	Have to much privileges
	Can crash the whole server

Web Application Solutions

Solutions deployed to the web application bin directory was the way to go in SharePoint 2007 when you wanted/needed to secure you application using CAS. This partial trust option is still valid in SharePoint 2010. Web application deployed solutions by default only have a very minimal CAS policy applied. Using custom CAS policies it is easy to give more privileges to assembly. Installing these solutions also requires a Farm Administrator but they are only applied to specific Web Applications. Updating the assembly does not require an application pool recycle.

Visual Studio 2010 have support for Web Application deployment but not for custom CAS policies. If you need custom CAS policies you need to hack some XML and you cannot use the F5-debugging experience in Visual Studio. Instead you have to install the solution using PowerShell or create your own Visual Studio SharePoint Deployment Steps.

Pros	Cons
Security policies can be configured and kept minimal	Only Farm Administrators can add new solutions (can be a pro also :-)
Minimal downtime when upgrading	No support OOB for custom CAS policies in Visual Studio 2010
Only crashes the web application

Sandboxed Solutions with User Code Proxies

There is actually a fourth option of deployment. And that is to use Sandboxed Solutions in combination with a full-trust User Code Proxy. A User Code Proxy is a special assembly and class that is registered in the GAC and running under full trust. This class exposes an operation that can be called by the Sandboxed code. Since it runs under full trust we can easily create a Proxy Operation that calls a web service or access other protected (from the Sandbox) sources. The proxy has to be registered by a farm administrator and is accessible to the whole farm, which means that all developers who knows about the assembly, class and operation can use the operation.

Since the User Code Proxy runs under full trust you need to be careful about that one. But if you design your application carefully the proxy operations should be kept to a minimum and quite small. This allows you to make the thorough code review on only a fraction of the whole application.

Tip: Make the User Code Proxies as Farm solutions which are registered using Feature activation and unregistered using deactivation of the Feature. Then your farm administrators can enable and disable them easy!