In my previous post, I outlined the new architecture. You
may have noticed how we no longer have urls containing relative paths. This is
because all of the components will be hosted on the same web role and I don’t
want to have to deal with complicated startup scripts to configure IIS,
therefore I want to try and use the Azure-provided methods as much as possible.
When deploying multiple sites to a single web role in Azure, there are
essentially two choices for setting it up.
- Virtual directories
- Sites
Using virtual directories involves nesting all of the secondary
services in the hierarchy of the main web role project (in this case the
website). The up side of this is that I could retain my current url structure. The
main down side of this is the inheritance of web.config settings. I initially
prototyped using this set up and spent a lot of time overriding entries from
the main web role config in the web.configs of the web and rest services to
prevent missing assembly and conflicting configuration errors.
An example of this is the following snippet from the
assemblies section in the web.config of the main website.
<add assembly="System.Web.Helpers, Version=1.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />
<add assembly="System.Web.Mvc, Version=3.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35, processorArchitecture=MSIL" />
<add assembly="System.Web.Abstractions, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />
<add assembly="System.Web.Routing, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />
<add assembly="System.Web.WebPages, Version=1.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />
<add assembly="System.Data.Linq, Version=4.0.0.0, Culture=neutral, PublicKeyToken=B77A5C561934E089" />
Looks harmless enough right? All of these assembly imports will
get inherited down to the monitoring site’s child projects, the ASMX web
service, and the Site and REST service. The latter 2 are also ASP.NET MVC so
it’s not a problem. However, the asmx web service has none of the system.web
assemblies in it, causing runtime errors post-deployment.
There were other items that caused me problems but this is
the most obvious example. In the end, I decided the virtual directory set up
was too brittle.
Using sites has the benefit of keeping all the individual
applications on the server separate, so a failure or change in one won’t affect
another. Because the applications are separate, we can’t use paths to
distinguish which application we want when our request hits the server, so
instead we use Host Headers.
The Host Header indicates the url that the user followed in
order to get to us. By using subdomains for each service, we can tell from the
host header which service the user is attempting to access.
The ServiceDefinition.csdef for the project looks like this.
<WebRole name="domain.Monitoring" vmsize="ExtraSmall">
<Sites>
<Site name="Web">
<Bindings>
<Binding name="Endpoint1" endpointName="Endpoint3" />
</Bindings>
</Site>
<Site name="Site" physicalDirectory="../../../../../AzPublish/Site-Release">
<Bindings>
<Binding name="Endpoint1" endpointName="Endpoint1" hostHeader="domain.com" />
<Binding name="Endpoint2" endpointName="Endpoint2" hostHeader="domain.com" />
</Bindings>
</Site>
<Site name="Gateway" physicalDirectory="../../../../../AzPublish/webservice-Release">
<Bindings>
<Binding name="Endpoint1" endpointName="Endpoint1" hostHeader="webservice.domain.com" />
<Binding name="Endpoint2" endpointName="Endpoint2" hostHeader="webservice.domain.com" />
</Bindings>
</Site>
<Site name="RESTService" physicalDirectory="../../../../../AzPublish/Rest-Release">
<Bindings>
<Binding name="Endpoint1" endpointName="Endpoint1" hostHeader="rest.domain.com" />
<Binding name="Endpoint2" endpointName="Endpoint2" hostHeader="rest.domain.com" />
</Bindings>
</Site>
</Sites>
<Endpoints>
<InputEndpoint name="Endpoint1" protocol="http" port="80" />
<InputEndpoint name="Endpoint2" protocol="https" port="443" certificate="DomainCertificate" />
<InputEndpoint name="Endpoint3" protocol="http" port="22202" />
</Endpoints>
The Binding
elements within each site define the endpoints that this site can be reached on
and the hostHeader attribute maps this application to the url the user followed
to get to us.
Notice how
the domain.Monitoring project has no domain header. This means that this project
will reply on endpoint3 (mapped to port 22202) for all traffic. Having it on a
separate port means there is no chance of it ever grabbing traffic from the
main projects.
You’ll
notice that the Monitoring project is the main project in this deployment (I’ll
go in to the monitoring project when I cover the traffic manager). The reason
for this is that I had some initial trouble getting the host header set up to
work with the Azure Traffic Manager and thought doing this may work. That later
turned out to be incorrect but I see no harm in keeping the monitoring project
as the main one here. Feel free to let me know if there are some caveats to
doing this that I am not aware of.
Only the main project in the web role is
compiled when publishing, so the ServiceDefinition needs to be pointed to a
location containing the compiled project. In order to achieve this, I use file
system deployment to publish the subprojects to the AzPublish folder. It’s not
ideal and I intend to get all this scripted in Powershell before we go live.
When I do that, I will of course publish the scripts on this blog. Also, if
there is a better way, please use the comments.
