I'm curious how auto scaling works with an Azure web application, specifically how each new instance gets a copy of the source code for the application.
Is this what happens, or is the source stored somewhere and each new instance points to it?
The entire virtual machine is duplicated. So usually you might have just one database but multiple apps receiving and processing the requests. If you need an "autoscaling" database too, then there are database solutions that handle syncronization across multiple machines, but in that case you're probably better off using Azure's native database which takes care of that.
Related
I am trying to understand the use of deployment slots for hosting my web app using the Azure app service.
I am particularly confused with the ideal ways to deal with the database while the swap is performed.
While maintaining two database versions seems like a solution, it adds the complexity of maintaining data across multiple databases to make them consistent.
What are the recommended ways for dealing with database schema and migrations while using blue/green deployments and in particular deployment slots?
Ideally you'll stage / production would share the same database, so it would not be an issue.
But if you have more slots, then you'd better also work with different databases and handle migrations during the release phase
We've worked through various solutions to this problem for a few years. There's not a toolset that provides a magic bullet for all cases. There are a few solutions:
Smaller databases/trivial changes
If it is possible to execute a migration script on a database that will complete in a second or two, and you can have an easy fallback script, you can execute the script concurrently with the swap. This can also be automated. But it's a higher stress situation and not one I'd recommend. This can even be done with EF Migrations.
Carefully ensure database compatibility between versions
Since we're dealing with a few hundred GB of data that cannot go down, we've just made it a rule that the database has to work with both versions of our application. It's not as awful or impossible as it sounds. For example, net new tables and fields can oftentimes be added before you even perform the swap. We test rollback between versions as part of our QA. If some fields need to be dropped, we wait until after the new version has been deployed and burned in, then run another script to perform the drops after we're sure we won't need rollback. We'll create new stored procedures when one needs to be upgraded so that the new version has its own. Example: sp_foo and sp_foo2.
We've had a lot of success with this strategy.
Slots are a feature specifically for App Services and not for DBs, if you want to use a specific DB with a specific slot then you setup the slot like this:
https://learn.microsoft.com/en-us/azure/app-service/deploy-staging-slots
Now when using Slots and swapping it also swaps App Configurations\Settings, and in App Settings you can have two DB connections strings but each with its own slot name and setting enabled. You can see it has been shown in this example here as well: https://learn.microsoft.com/en-us/azure/app-service/deploy-staging-slots#swap-two-slots
I want to create and host 4-5 websites using the same database. The only difference between the sites will be:
branding (colours and header)
data will be filtered per website (through sql query) and
Each site will be on a separate domain (but can be hosted on same server)
My 1st thought was to use API / Rest model and provision five front-ends in their own sub-domain. But as sites can be hosted on same server (I'm assuming one hosting account which enables multiple sub-domains), I think I can simply connect all sites with connection string to same database, avoiding complexities of using REST.
Is this possible and would i run into database conflicts doing this?
If later, I wanted to add a mobile app client, then will I need to build out a rest interface anyway?
Thanks
The right thing to do here depends a lot on your specific use case, expected load, preferred backend/edge technology, future plans, etc.
Site domains and servers -
The main point here is that you can host your domains/subdomains on the same or different servers. You simply need to update the DNS to point to the correct IP (update the subdomain's A record).
Note: If these sites are all public-facing, then I highly recommend using an edge/proxy server and even consider a load balancer, depending on expected number of visitors (Nginx, or Apache Web Server)
Decoupled architecture is almost always preferred -
I would definitely have an API/REST layer to abstract the database from the sites. This ensures that you establish a contract through which any clients can interact with the backend, including your mobile application. You also don't have to duplicate DB-specific code across the various clients. What if you decided to change your schema? Or even your database solution? Then all clients will be broken and your customers would be unhappy. As a guiding principle, think: if I change any one thing in my architecture, how many other things will need to change as a result? In terms of scalability, this architecture will also allow you to easily spin up more instances of whatever it is you need (databases, REST service, etc) should the need arise.
How do I build and deploy a REST API?Re: #2, to set up a simple custom REST service running on Node.js (and express), this is a good tutorial. The example also walks through setting up and integrating with an in-memory MongoDB database.
Database collisions?If you follow the above steps, this should be a moot point. Node.js/express and the databases expose ways to configure connection pools if the defaults do not suffice. Again, this will depend on your needs - how many concurrent users you expect.
I have been developing Windows Phone Apps for a while now, since WP7 first came out. I have written countless apps, but never actually released any that use an external service.
I am finally getting ready to release one of my first apps that requires a service, and have decided to go with Azure as my host.
Now for the question:
For this specific App, I need an offering that will allow me to host a very small amount of images and text, not even in the hundreds at this time. From what I have looked up, it seems like a database would be the preferred method of storing such a small amount of data, however, thinking into the future, would it be better for me to get the smallest table or blob storage (200gb) and use that? I will most likely be writing other apps that will most likely also require services, however, it is hard to tell what kind of services I would need. I could require a database rather than a blob if I am not storing images... or I may require a blob if I am, again, storing images...
If anyone has been in this situation before, which would you recommend, and why?
I would store images in blobs and other information in Table Services or Sql Database.
Which one to choose? It will vary according to your requirement.
See
http://blogs.msdn.com/b/writingdata_services/archive/2012/07/26/windows-azure-storage-sql-database-versus-table-storage.aspx
http://msdn.microsoft.com/library/azure/jj553018.aspx
I have a RESTful service running on azure. Currently, it has zero persistence. (It is just a REST gateway to another api.) I run it in a single, minimal Azure instance, and expect this will handle all the load this will ever get.
I now need to add some very lightweight persistence to it. A simple table, of 40-200 rows, eight data columns. The data is very static.
Doing the whole SQL Azure thing seems big overkill for my needs.
My thoughts have been to use:
An XML file, and load it into memory, as the db. XML file is
deployed with code.
Some better way to deploy XML, so it can be
rolled out/updated easier
SQL Compact (can I do this on Azure?)
___ ?
What is the right path here?
Thank you!
SQL Server Compact would need to store its data somewhere in persistent manner, so you would need to sync it regularly to a persistent storage and that's a lot of extra work and I have no idea how to do that reliably, so it's likely not a very good idea.
For your simple table the Azure Table Storage might be just enough. If that's not enough then SQL Azure is the next choice.
You can use the XML file as your store, there is no harm it it, rather this is a very easy and cost efficient solution, but there is a catch. As you mentioned currently you are using only azure instance, in this case you can store the XML file in your App_Data, but if in future if you want to shift to 2 azure instance, you will have to replicate the App_Data folder. In other words you will need to keep App_Data folder in sync.
Suggestion
Instead of storing file in App_Data store it in BLOB, you can retrieve it using WebClient and the store it in memory.
Pros: The advantage of BLOB is, you don't have to sync it.
Cons: There is a cost associated on the number of transactions you can make. This will depend upon how many times you update the file.
Summary
If you are going to work with only one Azure Instance, use App_Data
More than one Azure Instance, use BLOB with no syncing or use App_Data with sync.
Do not use Azure Table, as BLOB is the designated store provided for this purpose only.
EDIT
From MSDN post
As far as I know, Windows Azure does not support SQL Compact Edition. SQL Compact Edition stores data in file system which will not be synchronized in multiple instances (a web role may be deployed to more than one instance. An instance is similar to a virtual machine). And files stored in file system will lost when the instance is restarted or reimaged.
Hope this helps you.
I believe that the mvc mini profiler is a bit of a 'God-send'
I have incorporated it in a new MVC project which is targeting the Azure platform.
My question is - how to handle profiling across server (role instance) barriers?
Is this is even possible?
I don't understand why you would need to profile these apps any differently. You want to profile how your app behaves on the production server - go ahead and do it.
A single request will still be executed on a single instance, and you'll get the data from that same instance. If you want to profile services located on a different physical tier as well, that would require different approaches; involving communication through internal endpoints which I'm sure the mini profiler doesn't support out of the box. However, the modification shouldn't be that complicated.
However, would you want to profile physically separated tiers, I would go about it in a different way. Specifically, profile each tier independantly. Because that's how I would go about optimizing it. If you wrap the call to your other tier in a profiler statement, you can see where the problem lies and still be able to solve it.
By default the mvc-mini-profiler stores and delivers its results using HttpRuntime.Cache. This is going to cause some problems in a multi-instance environment.
If you are using multiple instances, then some ways you might be able to make this work are:
to change the Http Cache to an AppFabric Cache implementation (or some MemCached implementation)
to use an alternative Storage strategy for your profile results (the code includes SqlServerStorage as an example?)
Obviously, whichever strategy you choose will require more time/resources than just the single instance implementation.