Skip to main content

Improving the upload experience inside an Azure web application


In most of the cases, the latency problems are from the backend to our customers. They want to be able to access our data as fast as possible. Sometimes things are different, and the real challenge is to find ways how you can provide a reliable and fast way for customers to upload their content to the backend system.

Imagine that you have a system where agents around the world upload insurance policies every few minutes. The system is hosted in only one Azure Region – UK West. From the quality attributes of the system, there is no need to deploy the solution in multiple locations and building a native application or plugin for this purpose it is not acceptable (there is no business justification). Even so, agents are all around the world and the latency and internet speed, it’s a fact that needs to be handled.
At a high level, the system uses Azure Storage and Azure CosmosDB to store information that it is uploaded by agents. Agents are using a web portal and some REST API that runs inside Azure Web Apps. A horde of Azure Functions is crunking the uploaded content and push the content over Azure Service Bus to other backend systems that are out of our scope. Every day more than 5000 agents are online and on average, there are 500000 files uploaded every day.

Client requirement is simple:

Reduce as much as possible the latency and improve the upload experience of the agents. They complain that uploaded speed and application reliability is a big concern.


Let’s keep things as simple as possible and accept that deploying the solution in multiple locations it is not acceptable. Azure CDN can be used to cache content when you want to be closer to the customers, but we need the opposite thing.

The set of actions that we can take are:
(1) Improve the reliability of the system that handles the upload
(2) Improve the client experience on the web application
(3) Identify how you can bring the land zone closer to the agents

Upload reliability
The system already uses HTTPS protocol that offers pause and resume of an upload. To improve the performance and reduce the stress on the web application, we could rely on Azure Blob Storage. The agents could upload content directly to an Azure Storage – an upload link together with a SAS could be generated automatically.
From my experience, I notified that the scalability and reliability of uploading content directly to Azure Blob Storage is much higher vs implementing your own API.

Client experience

With the new capabilities that we have nowadays in the browser, we can upload content in the backend with the full capability of resume and do multi-part without having to write to much code. The agent can carry on with other tasks while the files are uploaded. JavaScript libraries enable us to offer a seamless experience in any modern browser. Filepond and Uppy are two great libraries that can be easily integrated inside the system.
The reliability of the connectivity is one of the biggest concerns, especially for agents that are using the system while they commute (e.g. unreliable connectivity when a train is inside a tunnel). In these situations, the client web application shall use the local storage to cache content and persist user information until the connectivity is restored. Combined with a Filepond, the client experience should be the same even if they lose connectivity for a few seconds or minutes.

Bringing file land zone closer to agents
There are multiple approaches to this problem. From the start, Azure CDN is not a viable solution; it is used to bring static content closer to customers and not the other way around. At this moment in time, there are 58 different Azure Regions around the globe. A simple solution would be to create multiple landing zones in different Azure Regions by measuring the latency between agents and the UK region.
After analyzing the latency and the agents' distribution, the decision was the following: Create Azure Blob Storages that are used as landing zones in the following Azure Regions:
  • UAE Central
  • Japan West
  • East Asia
  • North Central US
  • South Africa West
The backend system identifies the user location automatically and allocates the closest landing zone, that it is used by the client web application to upload the content. The agent is not aware related to the location where content is uploaded. Besides this solution, there are also other commercial solutions on the market, based on the same principle.
After doing a PoC we identify that the upload experience is not improved drastically by the solution. Why? Because the real issues were not from the latency as the client expected. It is from the way how the client web application is implemented.

Conclusion
After analyzing the above options, measuring the impact and the outcome, the results were the following.
  • By having multiple landing zones in different geographical locations, there is no real improvement to upload experience. The complexity of the system increases drastically without a real benefit.
  • The highest impact is by improving the client web application, adding offline and stateful capabilities. The latency and unreliable internet connectivity can be easilty overcome using a JavaScript library like Filepond that uploads content directly to Azure Blob Storage using a SAS. These, combined with a simple local database that cache agent data until the connectivity is reliable again has the most significant impact on the system. The selected JavaScript library for handling offline mode is Hoodie because of the strong integration with local and data storage.

Comments

Popular posts from this blog

ADO.NET provider with invariant name 'System.Data.SqlClient' could not be loaded

Today blog post will be started with the following error when running DB tests on the CI machine:
threw exception: System.InvalidOperationException: The Entity Framework provider type 'System.Data.Entity.SqlServer.SqlProviderServices, EntityFramework.SqlServer' registered in the application config file for the ADO.NET provider with invariant name 'System.Data.SqlClient' could not be loaded. Make sure that the assembly-qualified name is used and that the assembly is available to the running application. See http://go.microsoft.com/fwlink/?LinkId=260882 for more information. at System.Data.Entity.Infrastructure.DependencyResolution.ProviderServicesFactory.GetInstance(String providerTypeName, String providerInvariantName) This error happened only on the Continuous Integration machine. On the devs machines, everything has fine. The classic problem – on my machine it’s working. The CI has the following configuration:

TeamCity.NET 4.51EF 6.0.2VS2013
It seems that there …

GET call of REST API that contains '/'-slash character in the value of a parameter

Let’s assume that we have the following scenario: I have a public HTTP endpoint and I need to post some content using GET command. One of the parameters contains special characters like “\” and “/”. If the endpoint is an ApiController than you may have problems if you encode the parameter using the http encoder.
using (var httpClient = new HttpClient()) { httpClient.BaseAddress = baseUrl; Task<HttpResponseMessage> response = httpClient.GetAsync(string.Format("api/foo/{0}", "qwert/qwerqwer"))); response.Wait(); response.Result.EnsureSuccessStatusCode(); } One possible solution would be to encode the query parameter using UrlTokenEncode method of HttpServerUtility class and GetBytes method ofUTF8. In this way you would get the array of bytes of the parameter and encode them as a url token.
The following code show to you how you could write the encode and decode methods.
publ…

Entity Framework (EF) TransactionScope vs Database.BeginTransaction

In today blog post we will talk a little about a new feature that is available on EF6+ related to Transactions.
Until now, when we had to use transaction we used ‘TransactionScope’. It works great and I would say that is something that is now in our blood.
using (var scope = new TransactionScope(TransactionScopeOption.Required)) { using (SqlConnection conn = new SqlConnection("...")) { conn.Open(); SqlCommand sqlCommand = new SqlCommand(); sqlCommand.Connection = conn; sqlCommand.CommandText = ... sqlCommand.ExecuteNonQuery(); ... } scope.Complete(); } Starting with EF6.0 we have a new way to work with transactions. The new approach is based on Database.BeginTransaction(), Database.Rollback(), Database.Commit(). Yes, no more TransactionScope.
In the followi…