Using the Client in a Function-as-a-Service Environment

This section illustrates the best practices for leveraging the Elasticsearch client in a Function-as-a-Service (FaaS) environment. The most influential optimization is to initialize the client outside of the function, the global scope. This practice does not only improve performance but also enables background functionality as – for example – sniffing. The following examples provide a skeleton for the best practices.

Azure Functions

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Dependency injection in Azure Functions is built on the .NET Core Dependency Injection features. Azure recommends the use of the singleton lifetime for connections and clients (such as the ElasticsearchClient). The singleton service lifetime matches the host lifetime and is reused across function executions on that instance.

Your project will require the latest applicable version of the following packages:

Microsoft.NET.Sdk.Functions
Microsoft.Azure.Functions.Extensions
Microsoft.Extensions.DependencyInjection
NEST

using System;
using System.Threading.Tasks;
using Elasticsearch.Net;
using ElasticsearchExampleAzure;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Azure.Functions.Extensions.DependencyInjection;
using Microsoft.Azure.WebJobs;
using Microsoft.Azure.WebJobs.Extensions.Http;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;
using Nest;

[assembly: FunctionsStartup(typeof(Startup))]

namespace ElasticsearchExampleAzure
{
    // Use the startup method to configure services into the DI container.
    public class Startup : FunctionsStartup
    {
        public override void Configure(IFunctionsHostBuilder builder)
        {
            // Registering the ElasticClient as a singleton instance ensures we use the same underlying node pool for requests and
            // avoid first call overhead per invocation.
            builder.Services.AddSingleton(s => new ElasticClient(Environment.GetEnvironmentVariable("ELASTIC_CLOUD_ID"),
                new ApiKeyAuthenticationCredentials(Environment.GetEnvironmentVariable("ELASTIC_API_KEY"))));
        }
    }

    public class MyHttpTrigger
    {
        // Store the client in a private field for use from the function
        private readonly ElasticClient _client;

        // Add a constructor accepting the client which is provided by the DI container.
        public MyHttpTrigger(ElasticClient client)
        {
            _client = client;
        }

        [FunctionName("Function1")]
        public async Task<IActionResult> Run(
            [HttpTrigger(AuthorizationLevel.Function, "get", "post", Route = null)]
            HttpRequest req, ILogger log)
        {
            var response = await _client.PingAsync();
            return new OkObjectResult(response.DebugInformation);
        }
    }
}

GCP Cloud Functions

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To ensure reuse of the client and avoid a first request penalty per invocation, define it as a static field in the Function class. Once instantiated, it retains its value between invocations in the same execution environment. There is no guarantee that the state of a Cloud Function will be preserved for future invocations. However, Cloud Functions often recycles the execution environment of a previous invocation. If you declare a variable in global scope, its value can be reused in subsequent invocations without having to be recomputed.

Your project will require the latest applicable version of the following packages:

Google.Cloud.Functions.Hosting
NEST

using Elasticsearch.Net;
using Google.Cloud.Functions.Framework;
using Microsoft.AspNetCore.Http;
using Nest;
using System;
using System.Threading.Tasks;

namespace ElasticsearchExampleGCP
{
    public class Function : IHttpFunction
    {
        // Define a static client instance which is reused within the execution environment
        // Environment variables need to be configured to provide the cloud ID and API key we're going to use
        public static ElasticClient Client = new ElasticClient(Environment.GetEnvironmentVariable("ELASTIC_CLOUD_ID"),
            new ApiKeyAuthenticationCredentials(Environment.GetEnvironmentVariable("ELASTIC_API_KEY")));

        /// <summary>
        /// Logic for your function goes here.
        /// </summary>
        /// <param name="context">The HTTP context, containing the request and the response.</param>
        /// <returns>A task representing the asynchronous operation.</returns>
        public async Task HandleAsync(HttpContext context)
        {
            var response = await Client.PingAsync();
            await context.Response.WriteAsync(response.DebugInformation);
        }
    }
}

AWS Lambda

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Your project will require the latest applicable version of the following packages:

Amazon.Lambda.Core
Amazon.Lambda.Serialization.SystemTextJson
NEST

using System;
using Amazon.Lambda.Core;
using Amazon.Lambda.Serialization.SystemTextJson;
using Elasticsearch.Net;
using Nest;

// Assembly attribute to enable the Lambda function's JSON input to be converted into a .NET class.
[assembly: LambdaSerializer(typeof(DefaultLambdaJsonSerializer))]

namespace ElasticsearchExampleLambda
{
    public class Function
    {
        // Define a static client instance which is reused within the execution environment
        // Environment variables need to be configured to provide the cloud ID and API key we're going to use
        public static ElasticClient Client = new ElasticClient(Environment.GetEnvironmentVariable("ELASTIC_CLOUD_ID"),
            new ApiKeyAuthenticationCredentials(Environment.GetEnvironmentVariable("ELASTIC_API_KEY")));

        public void FunctionHandler(ILambdaContext context)
        {
            var response = Client.Ping();
            context.Logger.LogLine(response.DebugInformation);
        }
    }
}

Resources used to assess these recommendations:

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