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23Aug/180

Creating, Debugging and Deploying an Azure Function (Packt)

You can learn how to create, debug, and deploy an Azure Function by reading this tutorial by Daniel Bass, a developer who develops complex backend systems entirely on Azure, making heavy use of event-driven Azure Functions and Azure Data Lake.

Serverless programming has been a buzzword in technology for a while now, first implemented for arbitrary code by Amazon on Amazon Web Services (AWS) in 2014. The term normally refers to snippets of backend code running in environments that are wholly managed by the cloud provider, totally invisible to developers. This approach has some astounding benefits, enabling an entirely new paradigm of computing architecture.

This article will focus on Microsoft's serverless product, Azure Functions. In this article, you’ll create an Azure Function in Visual Studio, debug it locally, and deploy it to an Azure cloud instance. You can refer to https://github.com/TrainingByPackt/Serverless-Architectures-with-Azure/tree/master/Lesson%201 to access the complete code for this article.

To develop Azure Functions for production, you need a computer running Windows and Visual Studio 2015 or later; however, the smoothest experience is present in Visual Studio 2017, version 15.4 or later. If your computer can run Visual Studio, it can handle the Azure Function development.

Creating Your First Function to Receive and Process Data from an HTTP Request

Before you begin, confirm that you have Visual Studio 2017 version 15.4 installed; if not, download and install it. Visual Studio 2017 has a comprehensive suite of Azure tools, including Azure Function development. To do so, perform the following steps:

1. Open the Visual Studio Installer, which will show you the version of Visual Studio that you have installed and allow you to select the Azure Workflow and install it; if it is missing, then update Visual Studio, if required, to the latest version:

2. Click on Modify, select the Azure development workload, and click on Modify again:

Now, you can create a new Azure Function as a part of your serverless architecture that listens to HTTP requests to a certain address as its trigger. Begin by implementing the following steps:

1. Create a new solution. The example is called BeginningAzureServerlessArchitecture, which is a logical wrapper for several functions that will get deployed to this namespace.

2. Use the Visual C# Cloud | Azure Function Select the Empty trigger type and leave the default options, but set storage to None. This will create a Function App, which is a logical wrapper for several functions that will get deployed and scaled together:

3. You now have a solution with two files in it: host.json and local.settings.json. The local.settings.json file is used solely for local development, where it stores all details on connections to other Azure services.

It is important to note that when uploading something to a public repository, be very careful not to commit unencrypted connection settings - by default they will be unencrypted. host.json is the only file required to configure any functions running as a part of your Function App. This file can have settings that control the function timeout, security settings for every function, and a lot more.

4. Now, right-click on the project and select Add New Item. Once again, choose the Azure Function template:

5. On the next screen, select Http trigger with parameters, and set the Access rights to Anonymous. Right-click on your solution and select Enable NuGet Package Restore:

6. You will now have a C# file called PostTransactions.cs. It consists of a single method, Run, with an awful lot in the method signature: an attribute and an annotation. Some of this will be familiar to you if you are an experienced C# developer, and it is important to understand this signature.

Configuration as code is an important modern development practice. Rather than having servers reconfigured or configured manually by developers before code is deployed to them, configuration as code dictates that the entire configuration required to deploy an application to production is included in the source code.

This allows for variable replacement by your build/release agent, as you will (understandably) want slightly different settings, depending on your environment. Azure Functions implement this principle, with a configuration split between the host.json file for app-wide configurations and app settings, and the Run method signature for individual functions. Therefore, you can deploy an Azure Function to production with only the code that you find in the GitHub repository:

Outcome

You created an Azure Function, understood the roles the different files play, and learned about configuration as code.

The FunctionName annotation defines the name of the function within the Function App. This can be used for triggering your function, or it can be kept separate. The first parameter is an HttpRequestMessage object with an HttpTrigger attribute. This is what varies when you choose different triggers (for example, a timer trigger will have an object with a TimerTrigger attribute).

This attribute has several arguments. The first is the authorization level. Do you remember setting this when you created the function? It was called Access rights in the template. This defines the level of authorization that the function will demand of HTTP requests. The five levels are shown in the following table:

Authorization level Required information
Anonymous No key required; anyone with the path can call it an unlimited number of times.
User Need a valid token, generated by a user that has AD permission to trigger the Function App. Useful for high-security environments, where each service needs to manage its own security. Generally, token-based authentication is much more desirable than key-based.
Function Need the function key—a unique key created for each function in a Function App upon deployment. Any host key will also work. The most common form of authorization for basic deployments.
System Need the master key—a key at the Function App level (called a host key) that cannot be deleted but can be renewed.
Admin Need any host key.

One thing to bear in mind is that if you set a function to be high security and use System or Admin authorization, then any client that you give that key to will also be able to access any other functions in the Function App (if they can work out the path). Make sure that you separate high-security functions into different apps.

The next parameters are GET and POST, which define the HTTP verbs that will activate the function. Generally, from a microservices architecture point of view, you should only have one verb to prevent you from having to do bug-prone switching logic inside of the function. You can simply create four separate functions if you want GET,  POST,  PUT, and  DELETE on an artifact.

Finally, there is a string assigned to the property route. This is the only bit of routing logic that the function itself can see, and it simply defies the subpath from the Function App. It accepts WebAPI syntax, which you can see in the curly braces, / {name}. This will assign any text that appears where the curly braces are to a parameter called name.

This completes the HttpTrigger object. The three parameters left in the method signature are an HttpRequestMessage object, which allows you to access the HttpRequestMessage that triggered the function; a string parameter called name, which is what the string in the curly braces in the path will get bound to; and a TraceWriter for logging.

The current logic of the Function App can be seen in the following example, and you should see that it will take whatever name is put into it and send back an HTTP response saying Hello to that name.

Debugging an Azure Function

You now have a working Azure Function that can be deployed to Azure or run locally. You’ll first host and debug the function locally, to show the development cycle in action.

Debug an Azure Function

In this section, you'll run an Azure Function locally and debug it. You can develop new functions and test the functionality before deploying to the public cloud. And to ensure that it happens correctly, you'll require the single function created directly from the HTTP trigger with the parameters template.

Currently, your machine does not have the correct runtime to run an Azure Function, so you need to download it:

1. Click on the Play button in Visual Studio, and a dialog box should ask you if you want to download Azure Functions Core Tools - click on Yes. A Windows CMD window will open, with the lightning bolt logo of Azure Functions. It will bootstrap the environment and attach the debugger from Visual Studio. It will then list the endpoints the Function App is listening on.

2. Open the Postman app and copy and paste the endpoint into it, selecting either a POST or GET verb. You should get the response Hello {name}. Try changing the {name} in the path to your name, and you will see a different response. You can download Postman at https://www.getpostman.com/.

3. Create a debug point in the Run method by clicking in the margin to the left of the code:

4. Use Postman to send the request.

5. You are now able to use the standard Visual Studio debugging features and inspect the different objects as shown in the following screenshot:

6. Set your verb to POST, and add a message in the payload. See if you can find the verb in the HttpRequestMessage object in debug mode. It should be in the method property.

Outcome

You have debugged an Azure Function and tested it using Postman. As you can see from running the function locally, you, the developer, do not need to write any of the usual boilerplate code for message handling or routing. You don't even need to use ASP.NET controllers, or set up middleware. The Azure Functions container handles absolutely everything, leaving your code to simply do the business logic.

Activity: Improving Your Function

In this activity, you’ll add a JSON payload to the request and write code to parse that message into a C# object.

Prerequisites

You’ll require a function created from the HTTP trigger with the parameters template.

Scenario

You are creating a personal finance application that allows users to add their own transactions, integrate with other applications, and perhaps allow their credit card to directly log transactions. It will be able to scale elastically to any number of users, saving money when you don't have any users.

Aim

Parse a JSON payload into a C# object, starting your RESTful API.

Steps for Completion

1. Change the Route to transactions.

2. Remove the get Remove the String parameter called name:

3. Add the Newtonsoft.json package, if it isn't already present. You can do this by right-clicking on Solution Manage NuGet packages | Browse | Newtonsoft.json.

4. Right-click on the project and add a folder called Models, and then add a C# class called Transaction. Add two properties to this class: a DateTime property called ExecutionTime, and a Decimal property called Amount:

5. Use DeserializeObject<Transaction>(message).Result() to de-serialize the HttpRequestMessage into an instantiation of this class. To do this, you need to import the Models namespace and Newtonsoft.json. This will parse the JSON payload and use the Amount property to file the corresponding property on the Transaction object:

6. Change the return message to use a property of the new Transaction object, for example, You entered a transaction of £47.32!. Go to Postman and open the Body tab and select raw.

7. Enter the following JSON object:

8. Run locally to test. Make sure that you change the endpoint to /transactions in Postman.

Outcome

You learned how to access the HttpRequestMessage, and you will have a function that can read a JSON message and turn it into a C# object. During this subtopic, you debugged an Azure Function. Visual Studio only allows this through downloading azure-functions-core-tools. Unfortunately, it doesn't make it available on the general command line—only through command windows started in Visual Studio. If you want to use it independently, then you have to download it using npm. If you need to download azure-functions-core-tools separately, you can use npm to get it - npm install -g azure-functions-core-tools for version 1 (fully supported) and npm install -g azure-functions-core-tools@core for version 2 (beta). You can then use the debug setup to set Visual Studio to call an external program with the command func host start when you click on the Debug button.

This package is a lot more than just a debug environment, however; it actually has a CLI for everything you could possibly need in the Azure Function development. Open up a command window (in Visual Studio, if you haven't downloaded it independently) and type func help; you should see a full list of everything the CLI can do. Notable commands are func host start, which starts the local debug environment, and func azure {functionappname} fetch-app-settings, which lets you download the app settings of a function deployed to Azure so that you can test integration locally, as well. These need to be run in the same folder as the host.json file.

Deploying an Azure Function

An Azure Function is obviously geared towards being hosted on the Azure cloud, rather than locally or on your own computer. Visual Studio comes with a complete suite of tools to deploy and manage Azure services, and this includes full support for Azure Functions. The azure-functions-core-tools CLI that you downloaded to provide a local debug environment also has a set of tools for interacting with Azure Functions in the cloud, if you prefer CLIs.

It is possible to run Azure Functions on your own servers, using the Azure Functions runtime. This is a good way to utilize the sunk cost that you have already spent on servers, combined with the unlimited scale that Azure offers (if demand exceeds your server capacity). It's probably only worth it in terms of cost if you have a significant amount of unused Windows server time because this solution inevitably requires more management than normal Azure Function deployments. To deploy to Azure, you’ll need an Azure login with a valid Azure subscription.

Deploying to Azure

In this section, you'll deploy your first function to the public cloud and learn how to call it. You'll go live with your Azure Function start creating your serverless architecture. And to ensure that it happens correctly, you'll need a function project and a valid Azure subscription. You can begin by implementing the following steps:

1. Right-click on your project and select Publish.... Now select Azure Function App Create New as shown in the following screenshot:

2. Enter a memorable name and create a resource group and a consumption app service plan to match the following:

3. Click on the Publish button to publish your function.

4. Open a browser, navigate to http://portal.azure.com, and find your function. You can use the search bar and search the name of your function. Click on your Function App, and then click on the function name. Click on Get function URL in the upper-right corner, paste the address of your function in Postman, and test it. If you have a paid subscription, these executions will cost a small amount of money - you are only charged for the compute resources that you actually use. On a free account, you get a million executions for free.

Outcome

You now have a fully deployed and working Azure Function in the cloud.

This is not the recommended way to deploy to production. Azure Resource Manager (ARM) templates are the recommended way to deploy to production. ARM templates are JavaScript Object Notation (JSON) files. The resources that you want to deploy are declaratively described within JSON. An ARM template is idempotent, which means it can be run as many times as required, and the output will be the same each and every time. Azure handles the execution and targets the changes that need to be run.

If you found this article interesting, explore Daniel Bass’ Beginning Serverless Architectures with Microsoft Azure to quickly get up and running with your own serverless development on Microsoft Azure. This book will provide you with the context you need to get started on a larger project of your own, leaving you equipped with everything you need to migrate to a cloud-first serverless solution.

Cheers!

P.S. This post was provided by good people at Packt Publishing. Thank you, Ron!