Manage connections in Azure Functions

Here's an example of C# function code that creates a static HttpClient instance:

// Create a single, static HttpClient
private static HttpClient httpClient = new HttpClient();

public static async Task Run(string input)
{
    var response = await httpClient.GetAsync("https://example.com");
    // Rest of function
}

A common question about HttpClient in .NET is "Should I dispose of my client?" In general, you dispose of objects that implement IDisposable when you're done using them. But you don't dispose of a static client because you aren't done using it when the function ends. You want the static client to live for the duration of your application.

Because it provides better connection management options, you should use the native http.agent class instead of non-native methods, such as the node-fetch module. Connection parameters are configured through options on the http.agent class. For detailed options available with the HTTP agent, see new Agent([options]).

The global http.globalAgent class used by http.request() has all of these values set to their respective defaults. The recommended way to configure connection limits in Functions is to set a maximum number globally. The following example sets the maximum number of sockets for the function app:

http.globalAgent.maxSockets = 200;

The following example creates a new HTTP request with a custom HTTP agent only for that request:

var http = require('http');
var httpAgent = new http.Agent();
httpAgent.maxSockets = 200;
const options = { agent: httpAgent };
http.request(options, onResponseCallback);

CosmosClient connects to an Azure Cosmos DB instance. The Azure Cosmos DB documentation recommends that you use a singleton Azure Cosmos DB client for the lifetime of your application. The following example shows one pattern for doing that in a function:

#r "Microsoft.Azure.Cosmos"
using Microsoft.Azure.Cosmos;

private static Lazy<CosmosClient> lazyClient = new Lazy<CosmosClient>(InitializeCosmosClient);
private static CosmosClient cosmosClient => lazyClient.Value;

private static CosmosClient InitializeCosmosClient()
{
    // Perform any initialization here
    var uri = "https://youraccount.documents.azure.cn:443";
    var authKey = "authKey";
   
    return new CosmosClient(uri, authKey);
}

public static async Task Run(string input)
{
    Container container = cosmosClient.GetContainer("database", "collection");
    MyItem item = new MyItem{ id = "myId", partitionKey = "myPartitionKey", data = "example" };
    await container.UpsertItemAsync(document);
   
    // Rest of function
}

Also, create a file named "function.proj" for your trigger and add the below content :

<Project Sdk="Microsoft.NET.Sdk">
    <PropertyGroup>
        <TargetFramework>netcoreapp3.1</TargetFramework>
    </PropertyGroup>
    <ItemGroup>
        <PackageReference Include="Microsoft.Azure.Cosmos" Version="3.23.0" />
    </ItemGroup>
</Project>

CosmosClient connects to an Azure Cosmos DB instance. The Azure Cosmos DB documentation recommends that you use a singleton Azure Cosmos DB client for the lifetime of your application. The following example shows one pattern for doing that in a function:

const cosmos = require('@azure/cosmos');
const endpoint = process.env.COSMOS_API_URL;
const key = process.env.COSMOS_API_KEY;
const { CosmosClient } = cosmos;

const client = new CosmosClient({ endpoint, key });
// All function invocations also reference the same database and container.
const container = client.database("MyDatabaseName").container("MyContainerName");

module.exports = async function (context) {
    const { resources: itemArray } = await container.items.readAll().fetchAll();
    context.log(itemArray);
}